Welcome to the Subluxation Section @ Chiro.Org
Review the evolution of the Subluxation Complex.

What is the
Chiropractic Subluxation?

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:   Frankp@chiro.org

If there are terms in these articles you don't understand, you can get a definition from the Merriam Webster Medical Dictionary. If you want information about a specific disease, you can access the Merck Manual. You can also search Pub Med for more abstracts on this, or any other health topic.

The definition of subluxation, as adopted by the American Chiropractic Association
and the Association of Chiropractic Colleges is:

“A subluxation is a complex of functional and/or structural and/or pathological articular changes that compromise neural integrity, and may influence organ system function and general health.”

The subluxation has just recently been re-defined by the Rubicon Group and states:

“We currently define a chiropractic subluxation as a self-perpetuating, central segmental motor control problem that involves a joint, such as a vertebral motion segment, that is not moving appropriately, resulting in ongoing maladaptive neural plastic changes that interfere with the central nervous system’s ability to self-regulate, self-organize, adapt, repair and heal.”

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The classical definitions of subluxation are listed below:

The 5 Component “Vertebral Subluxation Complex” Model   [3, 4, 7, 8]

According to Kent: [1] Dishman [2] and Lantz [3, 4] developed and popularized the five
component model of the “vertebral subluxation complex” attributed to Faye. [5]

However, the model was presented in a text by Flesia [6] dated 1982, while the Faye's
notes bear a 1983 date.


The original model has five components:

1. Kinesiopathology – spinal pathomechanics, including alignment and motion irregularities, involving:

   • Hypomobility, segmental blockade, fixation:   Abnormal restriction of joint motion, OR
     

   • Hypermobility:   Abnormal increase in joint motion.
     

   • Compensation reaction:   Long term hypomobility causes the joint above the hypomobile area and occasionally the joint below to become hypermobile.
     

   • Loss of joint play:   The loss of normal vertical "joint slack/play" so that the joint becomes hypomobile on the vertical plane.
     

   • Loss of central axis of motion:   The loss of normal "Joint Slack/play" so that the joint becomes hypomobile on the rotational joint plane.
     

   • Positional dyskinesia, dynamic misalignment:   Joint misalignment throughout the entire range of motion of the involved joint.

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2. Neuropathophysiology, Neuropathology – compressed or facilitated nerve tissue, involving:

   • Compressive lesion, the pinched nerve, neurological hypoactivity:   The literature indicates that of the neurological damage induced by spinal kinesiopathologic changes, about 10–15% results in a compressive profile.
     

   • Facilitative lesion, the facilitative segment, neurological irritation, neurological hyperactivity:   The literature indicates that, of the neurological damage induced by spinal kinesiopathologic changes, about 85–90% results in a facilitated profile.
     

   • Articular neuropathy,   the hyaline cartilage pads in the diarthrodial spinal joints as well as the local articular ligamentous support tissue are seriously stressed during an acute episode of the vertebral subluxation complex and more so in long term uncorrected vertebral subluxation complex episodes. This causes, in addition to the histopathologically induced pathoanatomical changes due to long term uncorrected vertebral subluxation complex, significant damage to the balance and proprioceptive nerve endings (the Type I Mechano receptors, Type II & III Articular Receptors and Type IV Nociceptive 'Pain' Receptors) in the articular surfaces and the capsular ligaments so that "Noxious" nerve impulses are fired off afferently back to the spinal balance center in the cerebellum, the proprioceptor center in the cerebral cortex and in the Limbic 'joint pain' regions of the cerebral cortex. Surprisingly, the spinal cord stores facilitated data also, causing reflexogenic activity from the involved joint.

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3. Myopathology – muscle spasm, muscle weakness/ atrophy involving:

   There are parallel changes in the organ depots, of course. However, this is dealt with broadly under component #5. Myopathology is listed as a separate major component of the vertebral subluxation complex simply because myopathology is more readily testable and recognizable at the office level than are organ depot changes. The myopathological phenomenon associated with the vertebral subluxation complex are identical with myopathology induced by nerve damage due to other causes than spinal kinesiopathology. These changes can be referenced in many text books dealing with basic clinical pathology, clinical neuropathology and sports injuries.
   
   A.   From the compressive lesion:
   

   1. Neurological hypoactivity
      

   2. Hypotonus
      

   3. Atrophy
      

   4. Fibrosis (To varying degrees). The current literature points out that fibrosis in muscle tissue begins within one week of the original injury and becomes permanent within a few weeks. Krusen's Handbook of Physical Medicine and Rehabilitation, 1982, edited by Kottke, Stillwell, and Lehman. ISBN 07216-5501-7, chapter 18, pg. 391," Adhesion Formation." Experimental Models of Osteoarthritis: The Role of Immobilization, T. Videman, Clinical Biomechanics, 2:223–229, 1987, and the various papers by Videman there referenced. Managing Low Back Pain, 1st Ed. 1983, 2nd Ed. 1988; edited by W. H. Kirkaldy-Willis. 1st Ed. ISBN 0-443-08189-1 2nd Ed. ISBN 0-443-085358 Patholgenesis of Low Back Pain: Clinical Applications by Kirkaldy-Willis, MD, "Pathophysiology: Overview, Myofascial Cycle." These reports explain the progressive nature of fibrotic muscle degeneration, therefore leading to permanent spinal biomechanical aberrant function. Since, fibrosis begins within the first week after injury, and becomes irreversible shortly after that the basis for appropriate intervention within the three types of chiropractic care must be rethought.

   
   B.   From the facilitative lesion:

   1. Neurological hyperactivity
      

   2. Hypertonus
      

   3. Spasm
      

   4. Fibrosis (see above)

   
   C. From articular neuropathy

   1. "Erroneous" adaptation responses
      

   2. Adaptive spasm and weakness
      

   3. Resulting fibrous tissue (see above)

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4. Histopathology – inflammation, edema and swelling of tissue, usually local to the traumatized area, involving:

   Basically, histopathology is to be considered as the entire range of the inflammatory process. Uncorrected, this leads to fibrotic degeneration. In some cases this degenerative process leads to calcific salt deposition within the fibrous lattice. The literature presents three phases of fibrotic/ calcific ligamentous degeneration.

Phase 1 –   The original sprain.

Phase 2 –   The beginnings of fibrosis.

Phase 3 –   Complete fibrosis. Complete fibroses and the beginnings of fibrosis are not reversible, leading to permanent spinal biomechanical impairment. Bone degeneration is considered under component #5.

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5. Pathophysiology, Pathology, Biochemical Changes – pathophysiologic and pathoanatomical changes due to the previous four components usually seen locally as degeneration, fibrous tissue and/or erosion local and peripherally as a loss of global homeostasis.

A.   Local to the spine:


1. Bone degeneration-   Bone and soft tissue degeneration is an inevitable consequence of uncorrected spinal trauma (micro or macro) and to a degree, a result of a shifting postural alignment to gravity.
   

2. Bone regeneration-   A normal physiologic phenomenon. Bone regeneration alters architectural outlines of bone when the involved bone tissue becomes chronically out of alignment with gravity. This can be seen on spinal x-rays and is usually confused with the spinal degenerative process.

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Lantz   [5] has since revised and expanded the “vertebral subluxation complex” model
to include nine components:

The 9 Component Vertebral Subluxation Complex Model

1. Kinesiology
   
2. Neurology
   
3. Myology
   
4. Connective Tissue Physiology
   
5. Angiology
   
6. Inflammatory Response
   
7. Anatomy
   
8. Physiology
   
9. Biochemistry

He summarizes his objectives for expanding the model:   [5]

“The VSC allows for every aspect of chiropractic clinical management to be integrated into a single conceptual model, a sort of ‘unified field theory’ of chiropractic...Each component can, in turn, be described in terms of precise details of anatomic, physiologic, and biochemical alterations inherent in subluxation degeneration and parallel changes involved in normalization of structure and function through adjustive procedures.”

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The remainder of this page contains the collected articles written about the subluxation complex, including the:

• anatomical structures involved,

• degenerative changes that occur after a joint remains fixated over time,

• neurologic consequences following that fixation and/or inflammation,

• improvements that occur following chiropractic care,

• and the evolving development of subluxation theories.

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REFERENCES:

1. Models of Vertebral Subluxation: A Review
   J Vertebral Subluxation Research 1996; 1 (1): 1–6
   

2. Review of the Literature Supporting a Scientific Basis for the Chiropractic Subluxation Complex
   J Manipulative Physiol Ther 1985 (Sep); 8 (3) Sep: 163–174
   

3. The Vertebral Subluxation Complex PART 1:
   An Introduction to the Model and Kinesiological Component
   Chiropractic Research Journal 1989; 1 (3): 23–36
   

4. The Vertebral Subluxation Complex PART 2:
   The Neuropathological and Myopathological Components
   Chiropractic Research Journal 1990; 1 (4): 19–38
   

5. The Subluxation Complex.
   In: Gatterman MI,ed.
   Foundations of Chiropractic Subluxation.
   St. Louis, MO: Mosby, 1995
   

6. A Psychoepistemological Basis for the New Renaissance Intellectual.
   Renaissance International, Colorado Springs, CO, 1982
   

7. The Vertebral Subluxation Complex: An Integrative Perspective
   ICA International Review of Chiropractic 1992 (Mar): 25–27
   

8. Immobilization Degeneration and the Fixation Hypothesis of Chiropractic Subluxation
   Chiro Res J 1988; 1 (1) Spring: 21–46

The Anatomy Component of the Subluxation Complex

	Spinal Anatomy 101 A Chiro.Org info collection This page reviews the anatomy of vertebrae, describes the function of the “Spinal Motion Unit”, and clarifys which tissues suffer degenerative changes from the subluxation complex.
	The Anatomy and Morphometry of Cervical Zygapophyseal Joint Meniscoids Surg Radiol Anat. 2015 (Sep); 37 (7): 799–807 ~ FULL TEXT Meniscoids were identified in 86% of zygapophyseal joints examined; 50% contained both ventral and dorsal meniscoids, 7% contained a ventral meniscoid only and 29% contained a dorsal meniscoid only. Meniscoids were classified as adipose (4%), fibrous (74%), or fibroadipose (22%) based upon histological composition. There were no significant associations between meniscoid size (surface area or protrusion length) and gender, position in joint, spinal level, or articular degeneration. Increased articular degeneration was associated with fibrous meniscoid classification.
	Real-Time Visualization of Joint Cavitation PLoS One. 2015 (Apr 15); 10 (4): e0119470 ~ FULL TEXT Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking.
	Effects of Unilateral Facet Fixation and Facetectomy on Muscle Spindle Responsiveness During Simulated Spinal Manipulation in an Animal Model J Manipulative Physiol Ther. 2013 (Nov); 36 (9): 585–594 ~ FULL TEXT The apparent relationship between intervertebral joint mobility and the clinical success of spinal manipulation for LBP, combined with increasing evidence for proprioceptive-related changes in individuals with LBP led us to undertake a basic science investigation to determine the relationship between changes in lumbar spinal stiffness and mechanoreceptor activity from muscle spindles in the low back during a simulated High Velocity Low Amplitude spinal manipulation (HVLA-SM) in an animal preparation. The purpose of this study was to determine whether relative increases versus decreases in spinal stiffness can impact paraspinal sensory sensory responses over 5 thrust durations of HVLA-SM directed at the same level as the dysfunction. This study aims to be an important first step in concurrently examining the effects of intervertebral dysfunction and peripheral afferent signaling during a commonly used and effective therapeutic intervention for LBP.
	Evaluating the Relationship Among Cavitation, Zygapophyseal Joint Gapping, and Spinal Manipulation: An Exploratory Case Series J Manipulative Physiol Ther. 2011 (Jan); 34 (1): 2–14 ~ FULL TEXT Figure 1 summarizes the theory upon which this study was designed. Gapping is the separation of the zygapophyseal (Z) joint articular facets that occurs during spinal manipulative therapy (SMT) and side-posture positioning. [1] Zygapophyseal joint gapping during SMT is considered by many to be beneficial because the separation of joint surfaces during gapping is thought to   (1)   break up connective tissue adhesions that develop in hypomobile Z joints [2–4] (steps 1–5b, Fig 1) and   (2)   stimulate afferent nerves that innervate the Z joint capsule and the small muscles of the spine, [5–7] resulting in reflex neurologic [5, 8–16] (steps 3–5a, Fig 1) and possibly immunologic [15, 17, 18] consequences.
	Surgical Model of a Chronic Subluxation in Rabbits J Manipulative Physiol Ther. 1988 (Oct); 11 (5): 366–372 Critically needed in chiropractic research is an animal model of a subluxation that will allow experimental study. Previous attempts in this, as well as other, laboratories have been only minimally successful. We report here the development of a straightforward surgical method of producing a misalignment of the thoracic spine in rabbits, one that appears to be satisfactory for further study.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited FROM:   J Manipulative Physiol Ther. 2006 (Nov);   29 (9):   726–761 Anatomical Research The topic of anatomical research will be divided into studies that relate specifically to spinal manipulation/adjusting (SM) (“Studies Related to SM”) and those that add detail to the understanding of the spine (“Studies Adding to the Knowledge Base of the Spine”). Studies Related to SM Gapping of the zygapophysial joints Dysfunction of the spine that is treated by chiropractors has been described as the vertebral subluxation complex.   This complex, as described by Lantz [2] and Rosner, [3] has several components.   These components include myologic, connective, vascular, neurologic, and lymphatic tissue involvement.   Many hypothesize that a fundamental component of the vertebral subluxation complex is the development of adhesions in the zygapophysial joints (Z joints) after hypomobility of these structures. [4–6]   Spinal adjusting of the lumbar region is thought to separate the articular surfaces of the Z joints. [7–9]   This “gapping” is theoretically the action that “breaks up” adhesions.   Elimination of adhesions would allow the Z joints to become more mobile, thus helping the motion segment (2 adjacent vertebrae and the ligamentous structures connecting them) to reestablish a physiologic range of motion (ROM). [5]   Although the idea that gapping the Z joints would occur during a SM and that this action would break up adhesions seems logical to those who have performed these procedures, no anatomical or physiologic evidence existed [1] to show that gapping of the Z joints actually occurred, or that adhesions in the Z joints could potentially be broken until relatively recently. [10, 11]   Cramer et al [10, 11] found that in healthy volunteers, the lumbar Z joints did gap during both side-posture positioning and during chiropractic adjusting and the joints gapped significantly more during the latter procedure.   However, no reports have been published by any group regarding gapping of the Z joints in the low back pain population. Degeneration of the z joints after hypomobility Paris [12] has reportedly identified adhesions in the Z joints after hypomobility. More recently, degenerative changes have been identified in the Z joints of rats after induced hypomobility. [13]   See the section on Animal Models for further details. Advances in magnetic resonance imaging relevant to the spine and spinal adjusting Functional magnetic resonance imaging (MRI) evaluation of the spinal cord maps MRI signal changes following a specific stimulus designed to change neural activity. This procedure may become fundamental in the future workup of spinal cord injury [14] and may provide intriguing possibilities to the assessment of the spinal cord following procedures such as spinal adjusting. Diffusion and perfusion MRI provides information related to the structure and function of tissue at a microscopic level and will play a more prominent role in future neurovascular imaging. [15] As MRI at the molecular level becomes possible, opportunities for advances in research (and clinical practice) increase. [16] Research is also being done involving morphometry of the spine by means of MRI. [17] Morphometric measurements allow for an increased ability to study the structures influenced by chiropractic adjusting. [11, 17] Of related interest is that direct oblique cervical MRI provides more accurate assessment of all of the borders of the cervical intervertebral foramens (IVFs) than standard sagittal MRI. [11] Studies Adding to the Knowledge Base of the Spine Zygapophysial joints Between 15% and 40% of chronic low back pain is related to the Z joints. [18] The Z joint capsule receives a significant sensory innervation, [19, 20] much of which is probably related to nociception, that is, signaling potential or real tissue damage. The medial branches of the posterior primary divisions innervating a Z joint terminate as 1 of 3 types of sensory receptors: free nerve endings (nociceptive), complex unencapsulated nerve endings, and encapsulated nerve endings. The free nerve endings are associated with nociception. The ultrastructure of these receptors has been described. [20, 21] The Z joint capsules throughout the vertebral column are thought to do little to limit motion. [22] However, the capsules probably help to stabilize the Z joints during motions. [23] The gross and microscopic anatomy of the Z joint capsules has been described in detail. [23, 24] See the sections on Biomechanics and the Somatic Nervous System for further details of current research related to the Z joints and spinal adjusting. Ligaments of the spine Nerve tracing techniques indicate that stretching of spinal ligaments results in “a barrage of sensory feedback from several spinal cord levels on both sides of the spinal cord.” [25] The sensory information has been found to ascend to many higher (cortical) centers. Such findings provide provocative evidence that the spinal ligaments, along with the Z joint capsules, and the small muscles of the spine (interspinales, intertransversarii, and transversospinalis muscles) play an important role in mechanisms related to spinal proprioception (joint position sense) and may play a role in the neural activity related to spinal adjusting. [26] Recent work has also been done assessing the structure of spinal ligaments. The attachment sites and dimensions of the anterior and posterior longitudinal ligaments [27, 28] and the innervation and gross and light microscopic structure of the ligamenta flava [29, 30] and iliolumbar ligaments [31] have been studied in detail. The long posterior sacroiliac ligament may be important in transmitting loads from the lower extremity to the spine. [32] The strongest fibers course from the posterior superior iliac spine to the sacrotuberous ligament, and many important structures attach to this band, including the aponeurotic attachments of the common origin of the erector spinae muscle. The ligament is tensed during counternutation of the sacrum and slackened during nutation. [32] These findings are considered to be important by those involved with the study of the “kinetic chain concept” of load transmission from the lower extremity to the spine. The intervertebral disk and intervertebral disk degeneration Many relevant studies on the biology of the intervertebral disks (IVDs) have been completed in recent years. Disk degeneration is characterized by loss of fluid pressure, disruption or breakdown of collagen and proteoglycans, and sclerosis of the cartilaginous end plate and the adjacent subchondral bone. All of these hallmark signs of IVD degeneration can also occur as part of the normal aging process of the IVD. For these reasons, disk degeneration and normal aging of the disk are frequently discussed interchangeably, [33, 34] although the biochemical processes may be distinct. The IVD seems to age differently from other tissues, probably because of its lack of a blood supply, and the degenerative process may begin as early as 20 years of age (earlier in some cases). [33] In fact, certain teenagers may experience back pain because of IVD degeneration. [35] There is an extremely wide variation in aging and degeneration of the IVD. Some individuals in their 70s have disks of equivalent health to some in their 30s. The aging and degenerative stages of the IVD from prenatal development through the ninth decade of life have been worked out in considerable detail at the gross and light microscopic levels. [34–40] Calcification of the IVD during the aging process is much more common than was once thought, being found in 58.3% of subjects at autopsy. Such calcification is “significantly underestimated” by conventional radiography. [41] Several conditions promote or even possibly initiate disk degeneration. These include traumatic Schmorl's node formation, advanced aortic atherosclerosis, [42] and possibly, nicotine consumption. [43] The biochemistry of IVD degeneration is also being elucidated. In this regard, extruded nucleus pulposus has been found to spontaneously produce increased amounts of many chemokines that not only initiate a series of events that decrease the size of the IVD bulge but also result in IVD degeneration. [26, 35, 44–47] Intervertebral disk protrusion The normal mechanics of the IVD continue to be investigated. [33, 48–51] In addition, the mechanisms involved in IVD protrusion and failure have been studied in detail [35, 39, 52–62], as well as the effects of changing intradiscal pressure. [63, 64, 65] In addition, a set of terms to be used when describing bulging of the IVD was established by the International Society for the Study of the Lumbar Spine. [66] This terminology included disk bulge, protrusion (tearing of some inner layers of the anulus fibrosus with the nucleus extending into the radial tear), extrusion (tearing of all layers of the anulus fibrosus allowing nuclear material to enter the vertebral canal), and sequestration (a piece of extruded nucleus breaks off of the host IVD). Much recent research related to IVD protrusion in the cervical and lumbar regions (protrusion in the thoracic region has not been studied as extensively) has found that IVD protrusion is a very dynamic process and that after approximately 1 to 3 weeks, IVD protrusion will usually begin a 2-month to 1-year process of resolution, resulting in significant resorption and, from a patient's standpoint (ie, pain), often complete remission of signs and symptoms. [33, 67–69] In fact, histologic evidence of resorption of sequestered nuclei pulposi has been found, [70, 71], and shrinkage of protruded nuclei pulposi has been seen on both computed tomography and MRI. [72] This provides hope to patients with protruded IVDs and for those using conservative methods to treat this condition. Adenovirus-mediated transfer of genes and the resultant production of therapeutic growth factors are being investigated as a means to further study the biology of the IVD and the potential for treatment of disk degeneration [73]; however, the low vascularity of the adult IVD may preclude the effective use of gene therapy in IVD disease. [34] Two published studies have shown that the inhibition of tumor necrosis factor–a (TNF-a) (extruded nucleus pulposus contains high levels of TNF-a) by a monoclonal antibody (Remicade [infliximab], Centocor, Inc., Horsham, Pa) is successful in alleviating sciatica. [74, 75] Finally, the mechanisms of radicular pain continue to be studied. [41, 76–78] Innervation of IVDs The significant innervation of the IVDs continues to be investigated in detail. [79–82] Degenerated disks have been found to receive increased innervation by sensory fibers conducting nociception. [83] The added innervation seems to be stimulated by Schwann cells of the nerves innervating the outer aspect of the anulus fibrosus. [84] Consequently, injured or degenerated disks are likely to be more sensitive to pain than normal disks. Unique characteristics of the cervical IVDs The cervical IVDs have been found to differ significantly from the lumbar disks. Rather than being made up of many lamellae, the anulus fibrosus of each cervical disk is composed of a single, crescent-shaped piece of fibrocartilage that is thick anteriorly and becomes very narrow laterally and posteriorly. [85] Range of motion studies Noteworthy studies measuring both the ranges of motion in various regions of the spine (eg, cervical region) and the motions between individual vertebrae continue. The latter activity has led to studies attempting to better understand the concept of coupled motions in the spine. Finally, significant findings related specifically to motions in the sacroiliac joints have also been published in recent years. These findings are summarized next. Although ROMs (eg, cervical ROMs) can be measured reliably, [86] measurements made on different days of the same individual can vary considerably. [87] Coupled motion (eg, rotation of vertebrae during lateral flexion) of spinal segments continues to be actively studied. Current investigators are finding that: (1)   these motion patterns are very complex; (2)   all spinal motions are coupled motions; and (3)   coupling differs from 1 motion segment to the next. Furthermore, consensus has not been reached on many of these motion patterns. [88] The full ROM of the sacroiliac joint is not expressed until the extremes of hip motion are reached, moving an average of 7.5° (range, 3°–17°) in the sagittal plane during full flexion and extension of the hips. [89] Motions as high as 22° to 36° have been reported in preteen and early teenage children. [90] Contraction of the left and right transversus abdominis muscles increases stiffness of the sacroiliac joint, thus potentially reducing sprains of the ligaments that protect it. [91] Morphometric studies Morphometry means “measurement of an organism or its parts.” The past decade has seen many morphometric studies of various spinal structures. These studies allow for more accurate biomechanical and computer modeling (finite element analysis) studies to be performed and also allow for more accurate patient treatment protocols (surgical and manipulative) to be designed. Table 1 shows many of the morphometric studies performed since 1995, the region of the spine investigated, and the specific anatomical structure analyzed. Certain anatomical findings can best be discussed with each spinal region. The following sections describe anatomical findings of particular significance in the cervical, thoracic, lumbar, and sacroiliac regions. Each of the topics discussed is related to an active area of research. Anatomical Findings of Clinical Significance by Spinal Region: Cervical Region Connective tissue attachments to the spinal dura mater Connective tissue attachments to the posterior aspect of the spinal dura arising from the foramen magnum, posterior arch of C1, the spinous process of C2, [114] the rectus capitis posterior minor muscle, [115–117] the ligamentum nuchae, [118, 119] and the ligamenta flava between C1–C2 and C6–C7 [120, 121] have been described. These attachments may hold the dura mater posteriorly during cervical extension (to prevent buckling of the dura mater into the spinal cord) and flexion (to prevent the dura from moving forward and compressing the cord). Some authors have speculated that increased tension of the cervical paraspinal muscles may traction the connection between the rectus capitis posterior minor muscle and the dura, leading to headaches secondary to dural tension. [122] Others have proposed that tearing of these connective tissue attachments during the flexion component of flexion-extension (whiplash) type of injuries or other trauma to the cervical region could lead to buckling of the dura mater into the cervical segments of the spinal cord. Such dural buckling could conceivably result in the chronic neck pain, headaches, disorders of balance, and signs and symptoms of cervical myelopathy experienced by some patients who have had trauma to the cervical region. [118] The experimental work of Shinomiya et al [120, 121] lends support to these theories. In addition, homologous attachments in the lumbar region, called meningovertebral ligaments, have been shown to traction the dura mater and the related nerve roots after IVD protrusion. Vertebral artery The structure of the vertebral artery continues to be studied. The tortuosity of the vertebral artery can occasionally increase with severe, multilevel IVD degeneration. [123] Haynes et al [124] found that usually, there is no compression or stenosis of the vertebral artery with atlantoaxial rotation. Li et al [125] found that extreme extension and extension with rotation resulted in decreased flow in both vertebral arteries. Licht et al [126] found a decrease in flow in the vertebral artery contralateral to rotation and, for the first time, documented an increase in flow on the ipsilateral side of rotation. Mitchell et al [118] found a decrease in flow through both the left and right vertebral arteries (more in the contralateral vessel) with maximal rotation, especially in those arteries with underlying pathology (eg, atherosclerosis). Therefore, maximal rotation and extension seem to decrease flow through the vertebral arteries, but submaximal rotation seems to have less of an effect. Anatomical Findings of Clinical Significance by Spinal Region: Thoracic Region Idiopathic Scoliosis The cause of idiopathic scoliosis remains unknown, but it is thought to be the result of many factors. A genetic component [127, 128] to the disorder is likely with secondary factors that include a decrease in melatonin production [129–131] and a related increase in circulating levels of the hormone calmodulin. [128] Changes in skeletal muscle, [132] connective tissue [46, 47] bone density, rib distortion, [128] decreased height of the posterior vertebral arch, [133] asymmetry of the neurocentral synchondrosis, [134] and the relatively common finding (up to 26%) of syrinx formation and other neuroanatomical abnormalities in the spinal cord [135, 136] are probably the result of the altered biomechanics of the spine and spinal cord that occur with spinal curvatures. [128] In addition, increasing evidence exists supporting the theory that the primary disorder (probably related to genetic influences) is the involvement of high (cortical) brain centers involved in processing vestibular information. [137–139] An interesting study by D'Attilio et al [140] may indicate that there could be more than 1 subpopulation of patients with idiopathic scoliosis. These investigators showed that the alignment of the spinal column may be strongly influenced by dental occlusion and temporomandibular joint disturbance. These investigators reported that all 15 rats in an experimental group with an induced malocclusion developed thoracolumbar scoliosis within 1 week after the intervention. The scoliotic curvature was then completely resolved in 83% of these rats 1 week after correction of the malocclusion. None of the 15 untreated control rats in their study developed scoliosis. They suggested that an anatomical and functional relationship between the stomatognathic apparatus and the spinal column could explain their observations. They noted the presence of convergent sensory inputs to the craniocervical cord from stomatognathic and cervical spine structures and posited that a consequential tilt of the first cervical vertebra (C1) could affect the alignment of adjacent vertebrae, destabilizing the vertical alignment of the spine. Anatomical Findings of Clinical Significance by Spinal Region: Lumbar Region Many of the findings described previously in the section entitled “Intervertebral Disk” were related to the lumbar IVDs and will not be repeated here. Lumbar intervertebral foramina Transforaminal ligaments of the IVF can be identified on MRI, with a positive predictive value of 86.7%. [141] These ligaments are present in approximately 60.0% of lumbar IVFs (66.7% of L5–S1 IVFs) [141] and have been implicated as both a cause of low back pain and nerve root entrapment. [142–146] These structures can be quite sturdy (especially at the L5–S1 region) and can calcify. [147] They have been found to decrease the dimensions of the compartment transmitting the anterior primary division of the spinal nerve by 31.5%. [148] Limiting the size of the compartment in this way may, at times, contribute to the incidence of neurologic symptoms in the region, especially after trauma or secondary to degenerative arthritic changes in the region of the IVF. [148] Anatomical Findings of Clinical Significance by Spinal Region: Sacroiliac Joints Acquired accessory sacroiliac joints frequently (19.1%) form within the posterior (fibrous) portion of the joint. These accessory joints are more common in obese and older individuals and are also associated with other signs of degeneration and periodic low back pain. [149] Recommendations Continue to investigate the effects of spinal adjusting on the tissues of the spine and other organ systems (see section on Autonomic Nervous System) in various disease states (eg, gapping studies of the Z joints). Continue to evaluate the causes of hypomobility of vertebral segments in the general population, under what conditions such hypomobility is maintained, and continue to characterize the changes of the tissues of the spine after hypomobility (and possibly hypermobility) when normal activity is reestablished (ie, normal forces to the spine are reestablished) and also after spinal adjusting is added in an attempt to help reestablish normal forces and movement to hypomobile tissues. A combination of human and animal studies will be needed to achieve this recommendation. Evaluate the effects of spinal manipulative procedures on pain of radicular origin and on radiating pain. Further evaluation at the basic science level of the issue of vertebral and basilar artery iatrogenic pathology is warranted. Conduct descriptive studies to clarify regional differences (ie, between the cervical, thoracic, and lumbar regions) in the anatomy of the vertebral column and related spinal tissues. Conduct studies evaluating the normal development of all spinal tissues from embryogenesis through the mid 20s. Conduct studies further evaluating the aging spine (fourth through ninth decades). All of the recommendations above should be carried out in both human and animal studies at the gross (imaging and postmortem studies), light microscopic (biopsy specimens, eg, those obtained during surgery, cadaveric studies), and electron microscopic (biopsy specimens and postmortem studies) levels.

The Degeneration Component of the Subluxation Complex

NOTE:   All the related articles are listed below this Table.   Jump to Degeneration articles

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited FROM:   J Manipulative Physiol Ther. 2006 (Nov); 29 (9): 726–761 Measures of Pathologic States An intriguing question has begun to be answered relating to whether changes in intersegmental stiffness can be discerned using clinically available tools. Colloca et al [175] measured intersegmental impedance (dynamic stiffness) of lumbar vertebrae and correlated it with characteristics of vertebral height and IVD height measured from plain film radiographs. They found that there was a correlation between decreased disk height at L5–S1 and increased dynamic stiffness at the same segment. These findings were analogous to those of Kaigle et al [176] who, using a porcine model, also observed increased spine dynamic stiffness associated with degenerated disks, compared with normal controls. Using ultrasound indentation, another noninvasive approach, Kawchuk et al [177] also found that IVD degeneration in a porcine model resulted in decreased indentation for the same applied load. This is an analogous metric as spine stiffness. The use of ultrasound indentation in this animal model had high sensitivity (75.0%), specificity (83.3%), and accuracy (77.1%), compared with other approaches (arthroscopy, MRI, and plain film radiography). Two biomechanics studies have been performed to examine the effects of fixation (ie, a hypomobile subluxation) of the lumbar spine. Cramer et al [13] used a rat model of fixation in the lumbar spine by externally fixating the spinous processes of L4–L6 for up to 8 weeks. A principal finding due to the fixation was the development of osteophytes and degenerative articular changes of the facet joints within a few weeks. Reversal of some of the degeneration was observed for joints that were fixated for a short term (~1 week), but after 4 weeks, no reversal was observed. Little et al [178] simulated a hypomobile subluxation in intact, cadaveric human lumbar spine specimens by screwing a plate into the left anterior aspect of the L4 and L5 vertebral bodies. During physiologic motions of the fixated spine specimens for flexion, extension, and lateral bending, the motions at L4–5 were significantly decreased, whereas below and above that level, intersegmental motions were significantly increased. Correspondingly, the plane strains of the facet joint capsules were significantly decreased and increased at and above/below the site of fixation, respectively. Experimental Models to Study Somatic Inputs from the Paraspinal Tissues Since publication of the original white paper, 2 experimental animal models have been developed that facilitate study of the relationship between spinal biomechanics and neurophysiology in general and of SM specifically: a cervical spine model developed by Bolton and Holland [211] and a lumbar spine model developed by Pickar. [212] Additional animal models also relevant to chiropractic spinal adjusting are presented in the section on Animal Models later in this paper. The experimental preparations enable application of controlled mechanical loads to individual vertebra and, at the same time, provide access to the dorsal roots for recording neural activity from paraspinal tissues affected by the mechanical load. The discharge properties of primary afferents with receptive fields in paraspinal tissues and the effects of these sensory inputs on somatomotor, somatovisceral, and central neural processing can be determined. The preparations use a servo-driven motor to control the displacement of or force applied to the spinous process. Recently, a large animal model (goat) has been used to determine how strains in the facet capsule affect neural input from the capsule. [213] This model needs additional work to determine whether the capsule is sufficiently preloaded to enable accurate determination of strain and to confirm that identified neurons can be distinguished in the multiunit recordings. The preparations described in this section provide the opportunity to conduct neurophysiologic studies not possible in humans. With information obtained from these animal models, hypotheses can be formulated and then tested noninvasively in humans. Animal Models The remarkable scientific progress in both industry and medicine over the last 100 years has been responsible, in large part, to a transition from observational to experimental research. [305, 306] Human clinical studies contributed greatly to this progress, but animal studies have permitted investigators to perform experimental interventions that were not possible in human studies, and allowed a wider range of study designs. In addition, statistical power is easier to obtain in animal studies because large numbers of animals can be evaluated at relatively low costs, and animal study groups can be genetically homogeneous. Moreover, research animals are often bred to have genetic predispositions to illnesses that mimic those of humans, such as asthma, [307] cancer, [308] diabetes mellitus, [309] and hypertension. [310] These important features, and the ability to strictly control potentially confounding influences, make animal research an essential tool for today's health care researchers. Consequently, the need for animal models in chiropractic research has been acknowledged in each of the major reviews of scientific progress in chiropractic. [1, 311, 312] Despite this, some still question how we can learn anything about people from studying animals. The basis for this concern lies in the obvious anatomical and physiologic differences between humans and animals. Animal studies are generally used to examine fundamental mechanisms that are common to both humans and nonhuman species. In addition, as noted above, many human diseases can be mimicked in animal models. Consequently, animal research provides information about fundamental mechanisms common to both humans and animals, and often suggests new hypotheses for evaluation in subsequent human studies. The discovery of insulin provides an excellent example. It was also one of the most dramatic events in the history of health care research. [313] Animal studies showed that the pancreas was a critical organ in the development of diabetes mellitus. Additional work produced an extract of the pancreas that reduced hyperglycemia and glycosuria in animals that had been previously rendered diabetic by removal of the pancreas. After further extensive evaluation with laboratory animals, the purified extract was deemed ready for human tests. In the first human trial, a 14-year-old boy with severe diabetes received an intramuscular injection of the “purified” pancreatic extract but failed to show clinical improvement and developed a sterile abscess at the injection site. [314] However, on the strength of the previous animal studies, work continued to further purify the pancreatic extract, and additional human studies were conducted. These new human studies, using the purified extract, showed a tremendous clinical improvement in all subjects. [314] Therefore, animal studies revealed the critical role of insulin in diabetes, provided a source of the hormone for subsequent study, and showed the potential of insulin as a therapeutic agent. All of these events were necessary before human clinical trials of insulin could begin. In 1923, the Nobel Prize for Physiology or Medicine was awarded to Banting and Macleod, recognizing that the discovery of insulin had [315] “conferred the greatest benefit on mankind.” The current era of chiropractic experimental research began after the first federally funded workshop to examine SM, The Research Status of Spinal Manipulative Therapy, in 1975. [311] At the conclusion of this historical conference, it was widely acknowledged that little basic or clinical research data were available to evaluate the claims of clinicians using SM. Immediately after the first Research Agenda Conference in 1996, a white paper was published on the status of basic science research in chiropractic, "Basic Science Research in Chiropractic: The State of the Art and Recommendations for a Research Agenda". [1] A contemporary review by Vernon was cited in which 18 animal studies examined spine subluxation (1 historical monograph, 4 abstracts, and 13 articles). [316] A recent review by Henderson, Animal Models in the Study of Subluxation and Manipulation: 1964 to 2004, presents synopses of 34 animal studies (5 abstracts and 29 articles) published within the past 40 years. [317] In this review, studies were included if they specifically examined subluxation, the osteopathic lesion (somatic dysfunction), or SM. Studies examining subluxation or somatic dysfunction were grouped under the general term subluxation studies. These studies used animals to model either subluxation (31 studies) or SM (3 studies). The 31 subluxation studies examined either “full-mimic models” that attempted to induce spine fixation in intact animals (14 studies) or “component models” that emulated specific mechanical or chemical components attributed to spine subluxation (17 studies). The 3 SM studies used either manual (1 study) or instrumental interventions (2 studies). Subluxation Mimic Models Only 1 subluxation mimic model has been introduced since the 1996 Research Agenda Conference. This model, the external link model, combines surgically implanted spinous attachment units and an external link system to produce reversible, mechanical fixation of 3 adjacent lumbar segments (L4, L5, and L6) in the rat. [13] Cramer et al [13] used the external link model to examine degenerative changes after spine fixation. They observed stiffness and Z joint changes that developed within weeks after experimental fixation of a spine segment. Both the occurrence (number of involved segments) and severity (0–3 scale, least to most severe) of degenerative changes were recorded. These investigators reported significant differences in Z joint degeneration between fixed segments and nonfixed segments within the same animal. In addition, the occurrence and severity of articular degeneration and osteophyte formation on Z joints in rats with fixated vertebrae was significantly greater than similar degenerative changes, on comparable segments, in never-linked control rats. This subluxation mimic study provided strong evidence that decreased vertebral motion (vertebral fixation) produced degenerative changes in the Z joint that were greater for longer periods of fixation. Generally, these degenerative changes continued to progress after removal of the fixating links. However, the data also suggested that time thresholds exist, before which removal of the experimental fixation (links) may spontaneously reduce or reverse the fixation-induced degenerative changes. These time thresholds appeared to be earlier for facet surface degeneration (occurring between 1 and 4 weeks of fixation time) and later for osteophytic degeneration (occurring between 4 and 8 weeks of fixation time). In addition, facet degeneration was observed to occur earlier than osteophyte formation. The existence of these time thresholds is intriguing, and may have clinical significance. However, the authors warned that there is no known basis for projecting rat time frames to human subjects. Further work with this model and subsequent human studies are required to expand our understanding of these issues.

The Degenerative Component of Subluxation

The Chiropractic and Degenerative Joint Disease Page A Chiro.Org article collection This page contains many articles that explain the relationship between spinal subluxations and degenerative joint disease.

Radiologic Manifestations of Spinal Subluxations Chapter 6 from:   “Basic Chiropractic Procedural Manual” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter describes the radiologic signs that may be expected when spinal subluxations are demonstrable by radiography. Through the years, there have been several concepts within the chiropractic profession about what actually constitutes a subluxation. Each has had its rationale (anatomical, neurologic, or kinematic), and each has had certain validity contributing to our understanding of this complex phenomenon.

Spinal Degeneration Studies   ~ A brilliant series of studies See also our Degenerative Joint Disease and Chiropractic Page The following series of articles by Chuck Henderson, DC, PhD   (Palmer Center for Chiropractic Research) and Gregory D. Cramer, DC, PhD   (National University of Health Sciences) discuss the adhesions and degenerative changes that develop in zygapophyseal (Z) joints when a segment is subluxated.    Articular Cartilage Surface Changes Following Immobilization of the Rat Knee Joint. A Semiquantitative Scanning Electron-microscopic Study Acta Anat (Basel). 1996; 157 (1): 27–40 ~ FULL TEXT Normal articular cartilage surfaces are not flat and smooth, but are contoured with various degrees of roughness. We applied the articular surface classification system developed by Jurvelin to evaluate contour and surface quality changes in rat patellae after varying periods of knee joint immobilization. Numerous studies have demonstrated that joint immobilization induces degenerative changes in articular cartilage. We found a correlation between the duration of immobilization and changes in the measured area of contour and surface quality subclasses.    Degenerative Changes Following Spinal Fixation in a Small Animal Model J Manipulative Physiol Ther 2004 (Mar); 27 (3): 141–154 ~ FULL TEXT Fixed segments had more degenerative changes than nonfixed segments for all Z joint parameters (ANOVA, P <.0001). Osteophyte formation and ASD were directly dependent on duration of fixation. These findings indicate that fixation (hypomobility) results in time-dependent degenerative changes of the zygapophysial joints.   You will also enjoy reviewing this FCER-funded research project.    Introducing the External Link Model for Studying Spine Fixation and Misalignment: Part 1– Need, Rationale, and Applications J Manipulative Physiol Ther 2007 (Mar); 30 (3): 239–245 ~ FULL TEXT This is the first article in a series introducing a new animal model, the External Link Model that we propose will allow researchers to produce and study spine lesions with the cardinal biomechanical features of the chiropractic subluxation: fixation (hypomobility) and misalignment. After the first federally subsidized scientific workshop on spinal manipulation, The Research Status of Spinal Manipulative Therapy (1975), [9] General Chairman Murray Goldstein commented, “The lack of a relevant and reproducible animal model may be one important obstacle to clarification of these issues. …Thus, subluxation remains a hypothesis yet to be evaluated experimentally.” Unfortunately, this ‘important obstacle’ remained in place for more than a quarter century following this conference.    Introducing the External Link Model for Studying Spine Fixation and Misalignment: Part 2, Biomechanical Features J Manipulative Physiol Ther 2007 (May); 30 (4): 279–294 ~ FULL TEXT This study suggests that the external link model can be a valuable tool for studying the effects of spine fixation and misalignment, 2 cardinal features of what has been historically described as the chiropractic subluxation. Significant residual stiffness and misalignment remained after the links were removed. The progressive course of this lesion is consistent with subluxation theory and clinical chiropractic experience.    Preliminary Morphological Evidence That Vertebral Hypomobility Induces Synaptic Plasticity in the Spinal Cord J Manipulative Physiol Ther. 2007 (Jun); 30 (5): 336–342 ~ FULL TEXT These preliminary data suggest for the first time that chronic vertebral hypomobility at L4 through L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level. More definitive studies are warranted, and the biologic significance of these finding should be investigated.    Introducing the External Link Model for Studying Spine Fixation and Misalignment: Current Procedures, Costs, and Failure Rates J Manipulative Physiol Ther 2009 (May); 32 (4): 294–302 ~ FULL TEXT The great promise of basic chiropractic “subluxation” research is that it will clarify for clinical researchers the mechanisms by which spine fixation or malposition may cause harm and show or suggest effective therapeutic remedies. Answers are needed to pressing and fundamental questions such as: Does chiropractic subluxation actually occur? If so, does chiropractic spinal subluxation significantly threaten a patient's health? Are there features that will allow researchers and clinicians to determine its accurate and precise location as well as its specific nature? Can spinal manipulative therapy prevent, stop the progression, or reverse adverse health effects related to chiropractic subluxation? Are there “time windows” that might influence the outcome of treatment? When these questions are answered, clinicians will be able to more objectively match the unique features of a patient's presentation to the diversity of chiropractic techniques, treatment frequency, number of visits, and treatment duration.    Zygapophyseal Joint Adhesions After Induced Hypomobility J Manipulative Physiol Ther. 2010 (Sep); 33 (7): 508–518 ~ FULL TEXT Experimentally induced segmental hypomobility (fixation) of the lumbar Z joints resulted in time dependent intra-articular ADH formation. The ADH were found in approximately equal numbers in the left and right Z joints and were most prevalent in the peripheral regions of the joint from medial to lateral and cephalad to caudal. These findings are consistent with the hypothesis that hypomobility results in time-dependent degenerative changes and ADH development of the Z joints.    Spinous Process Hypertrophy Associated with Implanted Devices in the External Link Model J Manipulative Physiol Ther 2012 (Jun); 35 (5): 367–371 ~ FULL TEXT Recent development of a chiropractic subluxation mimic, the external link model, uses titanium implants on lumbar vertebrae in the rat. The objective of this study was to evaluate potential correlations in the model between linking history, bone resorption, exudate formation, and experimentally induced intervertebral hypomobility.

The Immobilization Degeneration & the Fixation Hypothesis of Chiropractic Subluxation Chiropractic Research Journal 1988; 1 (1): 21–46 ~ FULL TEXT The literature was reviewed concerning the effects of joint immobilization on the degeneration of articular and periarticular connective tissue. Every connective tissue component of an articulation is affected by immobilization, and each major component is discussed individually; these include the articular cartilage, synovium, articular capsule, periarticular ligaments, subchondral bone, the intervertebral disc and the meninges. Particular emphasis was placed on changes in the biochemical constituents of connective tissue, collagen, proteoglycans and hyaluronic acid, and the relation of these changes to alterations in the functional and biomechanical properties of the tissues. T hus an attempt is made here to establish a molecular basis for the theory and practice of chiropractic.

Surgical Model of a Chronic Subluxation in Rabbits J Manipulative Physiol Ther. 1988 (Oct); 11 (5): 366–372 Critically needed in chiropractic research is an animal model of a subluxation that will allow experimental study. Previous attempts in this, as well as other, laboratories have been only minimally successful. We report here the development of a straightforward surgical method of producing a misalignment of the thoracic spine in rabbits, one that appears to be satisfactory for further study.

The Neurologic Component of the Subluxation Complex

NOTE:   All the related articles are listed below this Table.   Jump to Neurology articles

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited FROM:   J Manipulative Physiol Ther. 2006 (Nov); 29 (9): 726–761 Somatic Nervous System Knowledge of and research directions for understanding the effects of chiropractic spinal adjusting on the somatic nervous system needs, as its basis, an understanding of neurophysiology as it relates to structure and function of the vertebral column. Thus, 2 areas are presented in this portion of the white paper. The first area beginning immediately below represents a substantial portion of our knowledge base for understanding the neurophysiologic properties of paraspinal tissues. The second area beginning with the section on Effects of SMs on Muscle and Muscle Spindles reviews how neural elements of the vertebral column and their organization are affected by SM. Information is included that predates the 1997 white paper when it was not included in that article. Experimental Models to Study Somatic Inputs from the Paraspinal Tissues Since publication of the original white paper, 2 experimental animal models have been developed that facilitate study of the relationship between spinal biomechanics and neurophysiology in general and of SM specifically: a cervical spine model developed by Bolton and Holland [211] and a lumbar spine model developed by Pickar. [212] Additional animal models also relevant to chiropractic spinal adjusting are presented in the section on Animal Models later in this paper. The experimental preparations enable application of controlled mechanical loads to individual vertebra and, at the same time, provide access to the dorsal roots for recording neural activity from paraspinal tissues affected by the mechanical load. The discharge properties of primary afferents with receptive fields in paraspinal tissues and the effects of these sensory inputs on somatomotor, somatovisceral, and central neural processing can be determined. The preparations use a servo-driven motor to control the displacement of or force applied to the spinous process. Recently, a large animal model (goat) has been used to determine how strains in the facet capsule affect neural input from the capsule. [213] This model needs additional work to determine whether the capsule is sufficiently preloaded to enable accurate determination of strain and to confirm that identified neurons can be distinguished in the multiunit recordings. The preparations described in this section provide the opportunity to conduct neurophysiologic studies not possible in humans. With information obtained from these animal models, hypotheses can be formulated and then tested noninvasively in humans. Sensory Input from Group I and II Afferents (Proprioceptive Afferents) Group I and II afferents are primary sensory neurons that convey information to the central nervous system from muscle spindles, Golgi tendon organs, and other low threshold mechanoreceptors such as Ruffini endings and Pacinian corpuscles. These afferents conduct action potentials rapidly (>35 m/s) due to their large diameters and heavy myelination. The structure and function of muscle spindles in the vertebral column have some unique aspects compared with those in the appendicular skeleton. Studies in animal models have described muscle spindles in the hind limb as single receptors located both deep in the muscle belly and close to the musculotendinous junction. [214–217] Spindle densities range from 5 to 45 spindles per gram of hindlimb muscle weight. [218] In the cervical spine of the human [219] and cat, [220, 221] however, muscle spindles are rarely seen as single entities, and their densities are greater than in peripheral musculature. In the cat, Richmond and Abrahams [220] describe cervical spindle complexes wherein 2 to 6 spindles are in close contact with each other or share capsules and/or intrafusal fibers. Spindle density can be 2 to 8 times higher (47–107 spindles per gram) in superficial cervical muscles [220] and 10 to 25 times higher (137–460 spindles per gram) in deep cervical muscles [221] than in hindlimb muscles. These differences in spindle densities between axial neck muscles and appendicular muscles appears similar in the humans. [222] In the lumbar spine of the cat, Carlson [223] identified muscle spindles in the longissimus, iliocostalis, sacrocaudalis, intertransversarii, multifidus, and interspinalis muscles, but quantification and morphological description of the spindles were not performed. Similarly, muscle spindles have been identified in the medial, intermediate, and lateral portions of the lumbar erector spinae in the human fetus. [224] Carlson [223] also noted that spindle density appeared higher in the central compared with peripheral portions of the longissimus. The high spindle density in the cervical and lumbar muscles is consistent with the high percentage of slow twitch fibers found in muscles of these 2 regions. [220, 223] The reflex organization of sensory input from paraspinal muscles spindles also has some unique aspects compared with that of the appendicular skeleton. A well-recognized concept related to the cat hindlimb is that the monosynaptic stretch reflex is elicited by excitation of muscle spindles. Afferents from each muscle spindle synapse upon a-motoneurons to that same muscle (homonymous a-motoneurons). [225–227] This stretch reflex arc uses a single excitatory synapse to homonymous a-motoneurons. [226, 228] The afferent arm of the reflex is comprised primarily of group Ia and possibly group II afferents. [227, 229] Each group Ia afferent from a given hindlimb muscle makes functional, monosynaptic connections with 50% to 100% of the homonymous a-motoneurons. [230, 231] Thus, stimulation of a group Ia afferent from a specific hindlimb muscle evokes a monosynaptic excitatory postsynaptic potential in all a-motoneurons to the same muscle. [232, 233] In contrast, in the cervical spine, the monosynaptic reflex connections to homonymous a-motoneurons are weaker. Excitatory postsynaptic potentials are smaller in amplitude, and group Ia afferents make functional connections with only 10% of the homonymous a-motoneurons. [234, 235] This probably contributes to the absence or weakness of monosynaptic reflexes in cervical muscle. [236] In the lumbar spine of the cat, stretch reflexes can be elicited from the longissimus muscle but not from the iliocostalis muscle. Conduction delays suggest that the reflex arc is not monosynaptic [237] unlike that in the hindlimb. [226, 228] The presence of monosynaptic stretch reflexes from the deeper lumbar muscles has not been determined. In humans, indirect evidence for the presence of muscle spindles and muscle spindle reflexes in lumbar paraspinal muscles was obtained by measuring evoked cerebral potentials in response to vibration of the lumbar paraspinal muscles, [238] which relatively selectively stimulates muscle spindles. [239] Muscle spindles, along with Golgi tendon organs, comprise a proprioceptive feedback system, which contributes to the sense of movement and position. [240–242] Abnormal sensory input from muscle spindles elicits limb lengthening illusions. [240, 243] When a vibrating mechanical stimulus (100 Hz) is applied to the Achilles tendon of a person standing erect with eyes closed, primary endings in the muscle spindle are excited. Because they monitor change in muscle length, the increased neural discharge signals to the central nervous system that the calf muscles are stretched or lengthened more than they actually are. Spindles increase their static firing rate by ~4 to 5 Hz per millimeter of muscle lengthening. [215] Because calf muscles normally lengthen as the body leans forward, the proprioceptive feedback error arising from the vibratory stimulus elicits a postural compensation in the form of backward sway. This movement compensates for the illusory forward flexion at the ankle. Recently, Wise et al [244] showed that spindles in muscles surrounding the elbow are sufficiently sensitive to signal 0.05° to 0.15° changes in elbow rotation. Thus, it seems reasonable to suppose that paravertebral muscle spindles can signal extremely small positional changes or movement of the vertebra to which their parent muscle is attached and, thus, contribute to control of intervertebral motions that might minimize or prevent noxious spinal loading. Recent findings in humans suggest that proprioceptive input from paravertebral muscle spindles is important for normal reflex activity and repositioning of the lumbar spine. For example, tapping the erector spinae muscles normally elicits short latency paravertebral EMG activity. However, vibration of the lumbar paravertebral muscles, which increases background spindle discharge, inhibits this reflex response. [245] Additional evidence indicates that proprioceptive input from spindles in the lumbar paravertebral muscles is necessary to accurately position the pelvis and lumbosacral spine. Although healthy individuals can accurately reposition their lumbosacral spine, their repositioning ability is impaired when muscle spindle discharge is increased by applying vibration to the lumbar paravertebral muscles. [246, 247] The correct position is consistently undershot because of the misperception of vertebral position. Interestingly, lumbosacral repositioning ability is impaired in individuals with a history of low back pain, but is improved in the presence of vibration, unlike normal individuals. [247] Proprioceptive input can alter muscle force directly via its effect on a-motoneuron excitability and indirectly via its effect on the excitability of segmental and suprasegmental interneurons. Even small changes in paraspinal muscle forces are thought to have a large impact on a motion segment's biomechanical behavior and stability. [248] For example, in vitro experiments accompanied by a modeling approach, which incorporated graded activity of 1 lumbar paraspinal muscle, showed an increase in vertebral stabilization as determined by decreases in the intersegmental neutral zone and ROM. Similarly, very small increases in lumbar paraspinal muscle activity at L2–L4 (1–3% of maximal voluntary contraction) were sufficient to restore segmental stability to the lumbar spine even under strenuous loading conditions. [249] More complex modeling that incorporates force vectors from 5 paraspinal muscles suggests that neuromuscular [250] mechanisms controlling multifidus muscle activity alone could functionally impact a lumbar motion segment especially during flexion-extension and axial rotation. A recent study suggests the presence of a previously unrecognized phenomenon in the lumbar multifidus and longissimus muscles that could affect proprioceptive mechanisms controlling paraspinal muscle function. [251] Changes in intersegmental positions in the lumbar spine that elongated the paraspinal muscles for 10 seconds desensitized paraspinal muscle spindles to subsequent vertebral movement when compared with intersegmental positions that shortened the paraspinal muscles. The findings suggested that either voluntary static postures or involuntary intervertebral positions, which are maintained for short durations, could elicit proprioceptive feedback errors and alter paraspinal muscle force. The spine may be particularly susceptible to this phenomenon because intersegmental positions are not under voluntary control, and a vertebra's spatial position is not uniquely determined at low loads. [252] Sensory Input from Group III and IV Afferents Group III and IV afferents from deep tissue (labeled as A-d and C-fibers, respectively, when from skin) are primary sensory neurons with mechanically, chemically, or thermally sensitive receptive endings. Some endings are sensitive to only a single modality; others are polymodal. Group III and IV mechanoreceptive endings can have high or low thresholds to mechanical stimuli. Those group III and IV endings that respond in a graded fashion to any stimulus that threatens or actually inflicts injury are called “nociceptors.” Group III and IV afferents conduct their action potentials slowly (=30 m/s) because of their small diameters and light myelination (group III) or lack of myelination (group IV). Deep tissues of the low back are innervated by afferent endings responsive to both mechanical and chemical stimuli. [253–259] For example, Cavanaugh et al [253] recorded multiunit activity from group III and IV afferents from the medial branch of the dorsal rami from deep connective tissue after removing lower back muscles in the rat. Gentle probing of the facet capsule, as well as forceful pulling on the supraspinous ligament, elicited a slowly adapting discharge from these afferent nerves. In a systematic study of 57 unmyelinated afferents from the tail and lumbar region of the rat, Bove and Light [259] found mechanonociceptive endings in muscle bellies, tendon, subcutaneous tissue, and neurovascular bundles. Up to a third of the afferents had receptive endings in more than 1 tissue. No receptive fields were found in the facet joint capsule. Pickar and McLain [258] recorded single-unit activity from group III and group IV afferents in the intact lumbar spine of cats during movement of the L5–6 facet joint. Most afferents, including 7 with receptive fields in or near the facet joint capsule, responded in a graded fashion to the direction of a nonnoxious load applied to the joint. Yamashita et al [256] found that only 20% of group III afferents in and around the lumbar facet joint had high mechanical thresholds (>8.5 g), as determined with von Frey–like hairs. This latter finding contrasts with afferents studied in the cervical spine where almost all group III afferents studied had high mechanical thresholds. [260] In addition, Bolton and Holland [211] found silent afferents innervating the cervical facet joints, which were only activated by firm, potentially noxious prodding of their receptive fields. Most unmyelinated mechanonociceptive afferents are also sensitive to chemical stimulation by capsaicin, but only 50% were sensitive to the inflammatory agent bradykinin. [259] Group III and IV receptive endings in and around the lumbar facet joint can be both activated and sensitized by chemical stimuli. Substance P increases their resting discharge by 80% and decreases their von Frey thresholds by –30%. [256] Similarly, carrageenan-induced inflammation increases the resting discharge of group III, group IV, and some group II afferents innervating the lumbar muscles and facet joints and sensitizes their receptive endings to mechanical stimuli. [257] The inflammation also activates previously silent group III and IV afferents. [257] In the cervical spine, group III afferents with a resting discharge were insensitive to the inflammatory mediator bradykinin, [260] but previously silent small-diameter afferents were activated by bradykinin. [211] These neural responses to inflammation likely underlie the findings that mustard oil induced inflammation elicits muscle activity in the neck. Mustard oil intensely activates high-threshold C-fibers (group IV afferents). [261] When very small volumes (20 µL) were injected into deep cervical paraspinal tissues, EMG activity was increased in a wide variety of upper cervical muscles including digastric, masseter, trapezius, and rectus capitis posterior. [262] Because the volume was small and its spread to the neighboring tissues was limited, the effects were likely mediated by a reflex. The large number of muscles affected by inflammation of cervical paraspinal muscles may relate to the hyperconvergence, described by Gillette et al [263] (see next paragraph), and to the communication between segmental paraspinal tissues via intersegmental connections within the spinal cord, reported by the laboratory of Pickar. [264] Dorsal horn neurons in the spinal cord with receptive fields in the lumbar paraspinal tissues, including paraspinal muscles and facet joints, receive more convergent input from group III and IV afferents than is true for dorsal horn neurons with receptive fields in the limbs. [263] In these electrophysiologic studies, Gillette et al [263] found that wide dynamic range and nociceptive specific neurons in the superficial dorsal horn of the L4–5 spinal segments shared receptive fields with deep and superficial tissues of the lumbar spine, the hip, and proximal leg. This type of input was termed hyperconvergent. Axonal tracing studies revealed that small diameter primary afferents from multifidus muscle and facet joints produce substantial bilateral labeling in laminae I, II, and III, as well as in the deeper laminae V–VIII and X. [265] Many of these laminae are involved in nociceptive processing and also project to autonomic centers. Axons Inside or Outside the IVF Adhesions, fixations, or discal herniation may produce an ectopic source of neural activity. Bove et al [266] inflamed the axons of mechanically sensitive group II, III, and IV afferents that innervate both superficial and deep structures. The inflammation led to increased spontaneous activity and/or increased mechanical sensitivity of only the group III and IV axons innervating deeper structures. Increasing evidence shows that the mechanical and chemical consequences of a herniated disk can affect neural tissue within the IVF. Dorsal roots and dorsal root ganglia (DRG) are more susceptible to the effects of mechanical compression than are axons of peripheral nerves because impaired or altered function is produced at substantially lower pressures. [267, 268] Applying as little as 10 mm Hg of pressure to the dorsal root reduces by 20% to 30% the nutritional transport to peripheral axons. [269] Recently, a mean pressure of 53 mm Hg (range, 7–256 mm Hg) was measured between a herniated disk and the nerve root in 34 humans undergoing surgery for lumbar disk herniation. [78] Song et al [270] inserted small pins into the IVF to model a space-reducing lesion in an animal model. Although pressures in the IVF were not measured, this lesion produced mechanical hyperalgesia in the hindlimb and increased the excitability of dorsal root ganglion cells. The application of nucleus pulposus to a lumbar nerve root increases spontaneous nerve activity and increases the mechanical sensitivity of dorsal root ganglion cells. [271] In addition, nucleus pulposus applied to a lumbar nerve root produces mechanical hyperalgesia, [272] causes swelling in and decreases blood flow to the DRG, and decreases blood flow to the lower leg. [273] Moderate doses of phospholipase A2, an inflammatory mediator associated with disk herniation, also increases the mechanical sensitivity of dorsal roots, produces long-lasting discharges, and increases the discharge of previously silent dorsal root ganglion cells. [41, 274] As mentioned in the previous section, extruded nucleus pulposus contains high levels of TNF-a, and 2 studies have shown that the inhibition of TNF-a by a monoclonal antibody (Remicade) is successful in alleviating sciatica. [74, 75] It should be noted that several case studies [201, 275, 276] and randomized clinical studies [277, 278] show that patients with herniated intervertebral disk, who received SM, gained clinical improvement. Effects of SMs on Muscle and Muscle Spindles Spinal manipulation induces somatomotor changes, that is, changes in muscle activity, apparently because of sensory input from the somatic nervous system. In asymptomatic patients, Herzog's group [279, 280] showed that PA spinal manipulative treatments applied to the cervical, thoracic, lumbar, and sacroiliac regions increased paraspinal EMG activity in a pattern related to the region of the spine that was manipulated. The EMG response latencies occur within 50 to 200 milliseconds after initiation of the manipulative thrust. Similarly, SM using an Activator-adjusting instrument applied to a transverse process elicited paraspinal EMG activity at the same segmental level but within 2 to 3 milliseconds. [281] This is surprisingly fast for a reflex response. Colloca and Keller [282] confirmed these latter findings in symptomatic patients with low back pain and, in addition, reported that the increased EMG activity, while beginning within 2 to 3 milliseconds of the manipulation, reached its peak within 50 to 100 milliseconds. Paraspinal EMG responses were greatest in magnitude when the manipulation was delivered close to the electrode site, and interestingly, the more chronic the low back pain, the less the EMG response. The EMG electrodes were not placed relative to any physical finding in the low back such as palpable muscle tension, as perceived by the practitioner or tissue tenderness as experienced by the patient. Spinal manipulation's effect on paraspinal muscle activity is not exclusively excitatory. In 1 symptomatic patient with spontaneous muscle activity in the thoracic spine, Herzog's group [280] observed reduced paraspinal EMG activity within 1 second after a thoracic SM. In a case series study, DeVocht et al [283] collected surface EMG activity from 16 participants in 2 chiropractic offices. Electrodes were placed over 2 sites exhibiting paraspinal muscle tension determined by manual palpation. Spinal manipulation was administered to 8 participants using Activator protocol. The other 8 were treated using Diversified protocol. EMG activity was decreased after treatment by both methods by at least 25% at 24 of the 31 EMG recording sites. The effects of SM on paraspinal EMG activity may also be associated with increases in muscle strength. Suter et al [284] studied symptomatic patients with sacroiliac joint dysfunction, anterior knee pain, and evidence of motor inhibition to knee extensor muscles. A side posture SM applied to the sacroiliac joint significantly decreased the inhibition of the knee extensors on the side of the body to which the manipulation was applied. Similarly, Keller and Colloca [285] found that erector spinae isometric strength (assessed using EMG) was increased after spinal compared with sham manipulation. A series of studies have addressed how SM affects central processing of somatomotor information. Spinal manipulation can increase the excitability of motor pathways in the central nervous system and depress the inflow of sensory information from muscle spindles to these motor pathways. This may, in part, account for the disparate clinical findings described above. In asymptomatic patients, Dishman et al [286] showed that SM increased central motor excitability. EMG activity from gastrocnemius muscle, evoked by direct activation of descending corticospinal tracts using transcranial magnetic stimulation, was larger after lumbar SM compared with simply positioning the patient but not applying the manipulation. However, SM can also depress the H-reflex. Manipulation applied to the sacroiliac joint in a PA direction decreased the magnitude of the tibial nerve H-reflex for up to 15 minutes in asymptomatic humans. [287] Similarly, side-posture lumbar manipulation of L5–S1 joint inhibited the H-reflex from the tibial nerve. [288] Mobilization alone but not massage also inhibited the tibial nerve H-reflex, but the effect of manipulation tended to be greater. [288, 289] After manipulation alone, the inhibition lasted for approximately 20 seconds but lasted up to 1 minute when the SM was preceded by spinal mobilization. Similarly, SM delivered to the cervical region depressed the median nerve H-reflex. [290] The magnitude of the response from the lumbar manipulation was greater than the response from the cervical manipulation, suggesting that central processing of sensory inputs from a SM is different in the neck and the low back. [290] The depression of the H-reflex does not appear to be a global response. Instead, it appears specific to the region of the spine manipulated because cervical manipulation did not affect the tibial nerve H-reflex. [291] Patient positioning, which flexes the lumbar spine before the manipulation, may augment the inhibition of tibial nerve the H-reflex. [292] A possible mechanism contributing to SM's inhibitory effects on the H-reflex and on spontaneous paraspinal EMG activity is suggested by recent experiments. Sensory input from tissues of the facet joint elicited by SM might reflexively decrease paraspinal muscle activity. Indahl et al [293] elicited reflex longissimus and multifidus EMG activity by electrically stimulating the intervertebral disk in a porcine preparation. Stretching the facet joint by injecting 1 mL of physiologic saline abolished the EMG activity. Haldeman's group [238, 294] has shown that SM can also affect higher centers in the brain. Using magnetic stimulation, Zhu et al [294] stimulated lumbar paraspinal muscles and recorded the evoked cerebral potentials. Stimulation of paraspinal muscle spindles using vibration reduced the magnitude of the cerebral potentials. Similarly, muscle spasm in human patients reduced the magnitude of the paraspinal muscle evoked cerebral potentials. Spinal manipulation reversed these effects, reducing muscle spasm and restoring the magnitude of the evoked cerebral potentials. [294] There is reason to believe that stretching the facet joint capsule and surrounding tissues likely occurs during SM, although this has received little study. [165] Furthermore, there may be reason to believe that the mechanically sensitive primary afferents could be stimulated beyond the short duration of an SM. Using MRI scans in human subjects, Cramer et al [10, 11] showed that a side-posture SM accompanied by cavitation gaps the facet joints. The synovial space of the lumbar facet joints increased in width an average of 2.2 mm in subjects who were positioned in side posture and received a side posture spinal adjustment. By comparison, the joint space widened by only 1.5 mm (a difference of 0.7 mm) in subjects who were positioned in side posture but did not receive a manipulation. The MRI scan was performed immediately after manipulation and lasted 20 minutes. Although not studied directly, it seems likely, based upon data from the laboratory of Khalsa, [165] that joint separations of these magnitudes are sufficient to load the facet joint tissues. If so, this raises the possibility that tissues surrounding the facet joint could be stretched for periods longer than the duration of the manipulation itself. Sensory input from tissues surrounding the facet joint that is graded with direction of facet movement [258] could elicit reflex muscle responses similar to those measured by Indahl et al. [293] Direct evidence from 1 of the experimental models described at the outset of this section [212] shows that the impulse load of an SM activates a variety of low-threshold mechanoreceptors in paraspinal muscles and that abrupt changes occur in the discharge from their parent afferent neurons [251, 295] as the speed of delivery approaches that used in clinical practice. [296–299] Pickar and Wheeler [251] recorded afferent activity from muscle spindle and Golgi tendon organ afferents having receptive fields in the lumbar multifidus and longissimus muscles while applying a spinal manipulative-like load to a lumbar vertebra. Muscle spindle afferents from lumbar multifidus and longissimus muscles were stimulated more by the impulse of an SM than by the load preparatory to the impulse (200% compared with 30%). Another type of low-threshold mechanoreceptor, a presumed Pacinian corpuscle, uniquely responded to the impulse of a manipulative-like load, that is, it did not respond to loads with a slower force-time profile. When an SM's duration was varied between 25 and 800 milliseconds, durations shorter than 400 milliseconds produced abrupt increases in discharge rates from 6 low-threshold mechanoreceptive afferents innervating the lumbar multifidus and longissimus muscles. [295] An increase in loading magnitude did not appear to systematically affect the discharge from these 6 low-threshold mechanoreceptors. Interestingly, Gillette et al [263, 265] showed that both weak and strong mechanical stimuli applied to paraspinal tissues can suppress spinal cord neurons that receive noxious input from the low back. In an anesthetized human patient undergoing an L4–L5 laminectomy, SM of the lumbosacral region evoked multiunit activity from the intact S1 nerve root. [300] This neural discharge measured in a clinical setting may be analogous, at least in part, to the discharge of low-threshold mechanoreceptors measured in an animal model. Effects of SMs on Pain or Pain Processing Numerous studies suggest that SM alters central processing of noxious stimuli because pain tolerance or pain threshold levels can increase after manipulation. In patients with low back pain, Glover et al [301] examined areas of lumbar skin that were painful to a pinprick. Fifteen minutes after SM of the lumbar region, the size of the area from which the pinpricks evoked pain was reduced, compared with the control group receiving detuned short wave therapy. Terrett and Vernon [302] quantified the reduction in pain sensitivity after SM using graded, electrical stimulation of cutaneous paraspinal tissues. A blinded observer assessed the minimal current necessary to evoke pain (pain threshold) and the maximal tolerable current that evoked pain (pain tolerance) in subjects with tender regions of the thoracic spine. Spinal manipulation significantly increased pain tolerance levels 1.5–fold within 30 seconds. Over the next 9.5 minutes, tolerance levels progressively increased up to 2.4–fold. In a case study, Vernon [303] assessed pressure/pain thresholds before and after SM using a handheld pressure algometer. The threshold measurement indicated the amount of pressure at which the perception of pressure changed to the perception of pain. The algometer was applied to 6 tender points in the neck region. The participant identified his own specific tender points. Spinal manipulation increased pressure-pain thresholds and decreased pain sensitivity by approximately 45% on average. In an effort to extend the findings in this case study, Cote et al [304] focused on chronic mechanical low back pain. A pressure algometer was applied to 3 sites in the lumbar region. The sites were standardized myofascial trigger points associated with low back pain. Unlike Vernon's earlier case study, these trigger points were not necessarily clinically relevant, that is, they were not identified as tender by participants, nor were they necessarily the most sensitive points for each individual. Unlike Vernon's case study, no changes in pressure-pain thresholds were observed. Recommendations and Action Steps “Nearly all proposed theories to explain the effects and mechanisms of action of SM have failed to withstand intense scientific scrutiny” (from the original white paper, Brennan et al [1]). This statement from the original white paper does not adequately express the state of chiropractic science. It seems more accurate to say that nearly all the proposed theories to explain the effects and mechanisms of action of SM have not been fully tested. Spinal manipulation is a biomechanical input generally delivered at high velocity. The question of how a short-lasting biomechanical input can presumably have long-lasting changes on a person's health needs answering. Research should seek to determine if SM produces long-term effects on biomechanics and/or neurophysiology. Determine the discharge characteristics (ie, the pattern or frequency of action potentials) of primary sensory neurons innervating the vertebral column in response to high-velocity loading. Determine how these patterns of activity affect the signaling properties of neurons in the central nervous system, for example, do they produce long-lasting changes. Determine if SM produces long-lasting changes in spinal biomechanics, which would presumably produce long-lasting changes in sensory input. Determine if SM produces long-lasting changes in neuromuscular control of paraspinal muscles, possibly comparing the use of fine wire electrodes with surface EMG or scanning EMG. Determine if paraspinal tissues have any unique physiology, compared with appendicular tissues, by comparing, for example, reflex changes initiated from sensory receptors in appendicular tissues with reflex responses initiated from sensory receptors in axial tissues. Identify objective changes in the vertebral column that lead one to think that SM is needed. Use new technologies to determine changes in intersegmental stiffness. Determine if hyperalgesia is associated with the manipulable lesion. Determine whether the manipulable lesion is inflamed and, conversely, if inflammation of spinal and paraspinal tissues can cause the manipulable lesion. General Recommendations.   A seed recommendation in the 1997 white paper (Brennan et al [1]) was to “concentrate basic science research at one lead chiropractic college and provide sufficient support personnel to conduct needed studies.” Acting on this recommendation in some way is sorely needed. A critical mass of chiropractic-oriented scientists able to easily interact and develop new ideas is critically important to drive chiropractic science. Basic and clinically-oriented basic scientists are scattered almost individually at chiropractic colleges and are isolated. This is in sharp contrast to the traditional university setting where a wide variety of fields are represented and allow for not only interdisciplinary collaborations but provide opportunities for informed discussion leading to inspiration and the writing and submission of research grants. Consideration should be given to the relative merits of developing basic science infrastructure at chiropractic colleges either in contrast to or in addition to establishing a small cadre of chiropractic scientists within a traditional university setting containing established infrastructure in terms of space, equipment and collaborative potential with established scientists from multiple disciplines.

The Biomechanical Component of the Subluxation Complex

NOTE:   All the related articles are listed below this Table.   Jump to Biomechanics articles

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited FROM:   J Manipulative Physiol Ther. 2006 (Nov); 29 (9): 726–761 Biomechanics Biomechanics is the study of the effects of loads applied to biologic cells, tissues or systems. Biomechanics has its origins from Galileo's studies of mechanics in general and his creation of the term mechanics as a subtitle of his book "Two New Sciences" (1638) to refer to force, displacement, and strength of materials. Arguably, the “father of biomechanics” is Giovanni Alfonso Borelli, who published in "De Motu Animalium" (1681) the principles of muscle movements based on statics and dynamics. However, the word “biology” and its concept as the study of living organisms did not occur until 1802 when the German naturalist, Gottfried Reinhold Treviranus, published his first volume "Biologie; oder die Philosophie der lebenden Natur". To rigorously understand SM and its effects requires an understanding of the principles of biomechanics. A.   Manipulation Forces Since the publication of the first white paper in 1997, there have been several important studies that have further clarified the loads that are applied during SM, and especially during high-velocity, low-amplitude (HVLA) SM. Triano and Shultz [150] measured the total force that was transmitted through the body during a side-lying lumbar or lumbosacral HVLA SM. The transmitted forces were similar to the applied forces for their temporal history, but the transmitted forces and moments were shown to vary substantially based on patient positioning. Herzog et al [151] measured the force distribution during thoracic HVLA SM and concluded that there was an important distinction between the total and effective applied forces, with the latter being much smaller than the total applied force. They found that the total peak force was being applied over a mean contact area of 34.8 cm2, but for the thoracic spine, the physiologic contact area of the transverse processes was only 0.25 cm2 (less than 1/100 of the total contact region). Hence, most of the total peak force was being applied to soft tissues (eg, skin, muscle, and fat), and only a small portion (~5 N) was being applied to the transverse process. A similar finding was reported by Kirstukas and Backman, [152] who reported that the “intense contact area” was on the order of 10 cm2 during thoracic HVLA SM. Clearly, the effective applied force during HVLA SM in general will vary based on the contact area of the manipulator's hand and the aspect of the vertebra, but in general, the effective force will be less, and sometimes substantially so, than the applied force. The 3-dimensional force applied during HVLA SM of the cervical, thoracic, and sacroiliac regions has now been measured. [153] The 3-dimensional data showed that forces in plane with the back (ie, Fx and Fy or shearing forces) always occurred during the SM, which was dominated by the normal (ie, Fz or perpendicular) applied force. The shearing forces were considerable in magnitude, ranging from a low mean of 15% (at T4–5) to a high of 29% (at sacroiliac) of the peak Fz force. As has been previously reported by others, [154] there was a consistent drop in the preload force magnitude just before the impulse portion of the HVLA SM, which is speculated to be due to a “countermovement” affect. The role of sex in developing force magnitude has been investigated. [155] The only previous report that compared male and female manipulators found no significant differences during HVLA SM using a patient simulator. [156] Forand et al [155] used an experienced matched group (range, 1–24.5 year of experience) of female and male chiropractors (14 per group) and found that there were no significant differences between sexes in thoracic HVLA SM forces. The one exception was that, in the lower thoracic spine, men applied significantly greater preload than did women. Another type of SM is mobilization or low-velocity low-amplitude SM, which is commonly used by physical therapists as well as other health professionals, including chiropractors. The general approach is to apply an increasing force over 5 to 10 seconds to determine the “end feel,” and then so calibrated, to apply a slow oscillation (~1 Hz for 10 seconds) about a mean graded force (I-IV arbitrary scale), which is less than the end feel. [157] Using an instrumented mobilization table, it was found that there was considerable variation in the force magnitudes used by experienced therapists for end feel, as well as grades I-IV mobilizations of L3 vertebra in healthy subjects. [157] When comparing treatment of younger vs older healthy subjects, it was found that, although mean forces were similar, smaller amplitudes and higher frequency of oscillations were used with older patients. [158] In a study of patients with nonspecific low back pain, there was considerable variation in the magnitudes of forces used, but the variation was strongly influenced not by the patient's severity of complaint but by the physical therapist's training. [159] B.   Effects of External Loading on Vertebral Displacements Our understanding of the kinematics of SM has been increased by 2 different types of investigations. First, Keller et al [160–162], have published 2 studies using mechanical force, manually assisted, short-lever SM (ie, Activator [Activator Methods International, Phoenix, Ariz] or very HVLA [VHVLA]) in vivo on patients undergoing lumbar surgery. Using forces ranging from 30 N (lowest setting) to 150 N (maximum setting) on the adjusting instrument, the vertebra where the force was applied had peak displacements of approximately 0.5 mm occurring within 10 milliseconds. Intersegmental displacements occurred of similar magnitudes but with large oscillations lasting 2 to 3 times longer (ie, 20–30 milliseconds), but all oscillations appeared to have damped out within 100 milliseconds. In a second in vivo study, they found that the vertebral displacements due to the Activator instrument were slightly larger (mean, ~0.62 mm) and did not vary significantly, depending on whether the instrument was positioned over the spinous process or facet joint (left or right). [163] 0 Second, using intact cadaveric human lumbar spine specimens, Ianuzzi and Khalsa [164] simulated lumbar HVLA SM while measuring vertebra kinematics and facet joint capsule strain. During simulated HVLA SM, the applied loads were within the range measured during in vivo HVLA SM. Vertebral translations occurred primarily in the direction of the applied load and were similar in magnitude (on order of 1–2 mm) regardless of manipulation site. Vertebral rotations (on order of 1°–3°) and facet joint capsule strain magnitudes (on order of 5%) during simulated HVLA SM were within the range that occurred during physiologic motions. [165] At a given facet joint capsule, distal manipulations induced capsule strains similar in magnitude to those that occurred when the manipulation was applied proximally. The mobility of lumbar vertebrae in healthy volunteers during mobilization has been assessed using dynamic MRI. Powers et al [166] found that applying a 10–second grade IV posterior to anterior (PA) mobilization (~100 N force) at the spinous process of a lumbar vertebra produced an extension of the vertebra ranging from a mean of 1.2° at L2 to 3.0° at L5. Using plain film radiographs, Lee and Evans [167] found similar displacements for a 150 N PA mobilization at L4. Kulig et al, [168] also using dynamic MRI, found that applying a PA mobilization induced intersegmental motion in all lumbar vertebrae, caudal and cranial, to the site of applied force. This is consistent with the findings of Ianuzzi and Khalsa [164] who also found that simulated HVLA SM at a single vertebra induced motion in all other lumbar vertebrae. Thus, it is not possible to move only a single vertebrae with SM (high or low velocity) because the spine is a linked and coupled structure. Other effects HVLA SM is commonly associated with a “cracking” sound, which has previously been shown to be associated with a cavitation phenomenon in the facet joints. [169, 170] In healthy volunteers, Ross et al [171] found that single HVLA SM were typically associated with multiple cavitations (ranging from 2 to 6), which were from nearby vertebrae. This was consistent with the findings of Beffa and Mathews, [172] who found no significant relationship between the location of the cavitation and HVLA SM of the L5 or sacroiliac joint in asymptomatic volunteers. There is some question as to whether HVLA SM can actually induce motion into the sacroiliac joint, as Tullberg et al, [173] using stereo radiography, were unable to measure any significant motion of the sacrum relative to the ilium after a combination of HVLA and mobilization SM in patients with “subluxated” sacroiliac joints. Furthermore, Flynn et al [174] found no association between an “audible pop” and improvement in ROM, pain, or disability in patients with nonradicular low back pain. C.   Measures of Pathologic States An intriguing question has begun to be answered relating to whether changes in intersegmental stiffness can be discerned using clinically available tools. Colloca et al [175] measured intersegmental impedance (dynamic stiffness) of lumbar vertebrae and correlated it with characteristics of vertebral height and IVD height measured from plain film radiographs. They found that there was a correlation between decreased disk height at L5–S1 and increased dynamic stiffness at the same segment. These findings were analogous to those of Kaigle et al [176] who, using a porcine model, also observed increased spine dynamic stiffness associated with degenerated disks, compared with normal controls. Using ultrasound indentation, another noninvasive approach, Kawchuk et al [177] also found that IVD degeneration in a porcine model resulted in decreased indentation for the same applied load. This is an analogous metric as spine stiffness. The use of ultrasound indentation in this animal model had high sensitivity (75.0%), specificity (83.3%), and accuracy (77.1%), compared with other approaches (arthroscopy, MRI, and plain film radiography). Two biomechanics studies have been performed to examine the effects of fixation (ie, a hypomobile subluxation) of the lumbar spine. Cramer et al [13] used a rat model of fixation in the lumbar spine by externally fixating the spinous processes of L4–L6 for up to 8 weeks. A principal finding due to the fixation was the development of osteophytes and degenerative articular changes of the facet joints within a few weeks. Reversal of some of the degeneration was observed for joints that were fixated for a short term (~1 week), but after 4 weeks, no reversal was observed. Little et al [178] simulated a hypomobile subluxation in intact, cadaveric human lumbar spine specimens by screwing a plate into the left anterior aspect of the L4 and L5 vertebral bodies. During physiologic motions of the fixated spine specimens for flexion, extension, and lateral bending, the motions at L4–5 were significantly decreased, whereas below and above that level, intersegmental motions were significantly increased. Correspondingly, the plane strains of the facet joint capsules were significantly decreased and increased at and above/below the site of fixation, respectively. Diagnostic tools or outcome measures The principal biomechanical “tool” still used by most chiropractors is palpation. As such, there has been a continued investigation into factors that change what is felt during palpation. Humans are relatively good at discriminating different magnitudes of stiffness for purely “elastic” materials. [179] However, the human spine responds as a viscoelastic system, in which the speed of force application changes the apparent stiffness. Nicholson et al [180] have shown that the relatively poor ability of clinicians to accurately estimate spine stiffness magnitudes is likely due to a 50% poorer ability to discriminate viscous components of viscoelastic systems. Latimer et al [181] found that therapists used different forces to discern spine stiffness and, hence, had different internal perceptual scales. By training therapists to use a calibrated stiffness instrument, discrimination of PA stiffness in the spine can be done with relatively high interexaminer reliability. [182] Furthermore, objective instruments have been developed that can reliably measure PA spine stiffness. [183] Perhaps, the most important aspect of using palpation to detect subluxations (ie, a “manipulable lesion”) is standardization of training. [184] When examiners are trained in a standardized fashion, they are able to obtain relatively high interexaminer reliability (? = 0.68) for detecting cervical fixations. Stiffness of the spine is influenced by many factors. If the ribcage is constrained, then the stiffness measured at T12–L4 can be significantly increased. [185] Change in orientation of an applied load to the spinous process can have small yet significant changes in objectively measured stiffness. [186] Furthermore, because the spine is a viscoelastic system, there will be a preconditioning effect when applying loads, such that after preconditioning the spine with standard mobilization SM, there will be no measurable change in stiffness. [187] There has also begun to be a growing appreciation for the natural (and normal) variability in spine stiffness as assessed by standard ROM tests during a physical examination. Christensen and Nilsson [87] found that in asymptomatic volunteers during a 3-week period, there was an intrinsic variability in ROM of the cervical spine of ± 20°, ± 14°, and ± 12° for flexion/extension, lateral bending, and rotation, respectively. In contrast, repositioning the head to the neutral position, which is related to proprioception, is done with relatively high fidelity over the same period. [188] Asymptomatic volunteers were able to reachieve the neutral zero position of their heads with a mean difference of 2.7°, 1.0°, and 0.7° for the sagittal, horizontal, and frontal planes, respectively. Using a case study approach, Lehman and McGill [189] observed that a single HVLA SM session in the lumbar spine caused notable changes in biomechanical factors associated with a complex task (ie, a golf swing in an experienced golfer who had chronic low back pain). In addition to changes in vertebral kinematics, they observed decreased electromyographic (EMG) responses of the associated lumbar muscles. In a subsequent study, Lehman and McGill [190] found that lumbar HVLA SM in patients with low back pain resulted in variable changes in lumbar ROM and associated muscle EMG. The largest changes were associated with patients with the greatest reported pain. In a review of the available literature. Lehman [191] reported that, currently, the best way to discriminate between normal and low back patient groups was using biomechanical tests that assessed “higher-order kinematics during complex movement tasks.” Simpler end ROM tests had poor predictive ability. Another commonly performed clinical test is measuring leg lengths, especially in the prone position. Using a special designed table to minimize friction and allow independent loading of each leg, Jansen and Cooperstein [192] determined that the prone leg length test was reliable for detecting non–weight-bearing asymmetry in leg lengths. Nguyen et al [193] found that there was reasonable concordance (? = 0.6) in determining whether a short leg was present using the Activator protocol. Cooperstein et al [194] found that it was possible to detect a leg length difference of 1.9 mm but recommended that only differences of greater than 3.7 mm should have confidence associated with them. D.   Mathematical and Computational Models One of the signs of maturity of any field is the ability to produce predictive models. In spine biomechanics, most models are computationally based and either use finite element approaches [195] or optimization with minimization of an objective function. Analytical approaches have also been performed, which include a linear elastic model of a lumbar motion segment. [196] This model successfully predicted loads born by various ligaments under physiologic loads. Solinger [197] created a model that predicted the dynamic response of L2–L3 to impulsive loads on the order of those used in VHVLA SM. Using a lumped parameter approach, Keller and Colloca [198] created an analytical model that predicted the frequency dependent response of the human lumbar spine to PA forces applied to the spinous processes, as is done during low velocity and low amplitude (ie, mobilization), HVLA, and VHVLA (ie, Activator). An alternative approach was adopted by Dulhunty [199] who modeled force transmission in the cervical spine to predict whether parallel forces or concurrent forces are the optimization function. A relatively new approach in spine modeling, especially in the lumbar spine, is to incorporate what are called “follower loads” for muscles. The issue is that the ex vivo (cadaveric) intact lumbar spine will buckle under compressive loads of ~100 N, whereas in vivo, the lumbar spine easily supports compressive loads of ~1000 N (ie, 10 times greater). Patwardhan et al [200] found that by modeling muscle activation so that their loads followed the tangent of the lumbar lordosis, their model would approximate the in vivo condition. A couple of new comprehensive models have been advanced to explain how the spine becomes subluxated in the first place and how SM can restore it to “normal.” Triano [201, 202] has advocated a mechanical model based on the concept of intersegmental buckling, which was based on original observations by Wilder et al [203, 204] and fluoroscopic recordings of a buckling event in a weightlifter by Cholewicki et al [205] and Cholewicki and McGill. [206] Essentially, this model proposes that there is a balance point between each pair of vertebrae that under certain loading conditions can suddenly shift, which then results in increased tissue strain of associated soft tissues (eg, facet joint capsule). The increased tissue strain can result in small tears and associated biologic inflammatory response. Evans et al [207] have proposed an optimization model where the spine system is biased toward minimizing the mechanical energy associated with loading the spine. Their model is described for the case of linear elasticity, although they claim it is also apropos of nonlinear elasticity. As with any theory (or model), the value of these new theories is really found in their predictive ability and how well their predictions are validated by experimental data. So far, neither of these theories has been tested to any degree. E.   Instrumented Manipulation Passive devices have been used for many decades to treat patients with back disorders. Recently, a simple distraction device, Rola Stretcher (Unique Relief, Inc, Davenport, Iowa), designed to be used at home without supervision, was tested to determine whether it showed any lengthening of the spine subsequent to its use. Devocht et al [208] tested 12 asymptomatic adults and found a significant increase in sitting height after 10 minutes of lying supine on the device. They concluded that it at least temporarily lengthened the spine, presumably by increasing the intervertebral disk height. In addition to the activator adjusting tool, which has had increasing amounts of scientific study, [160–163] the PulStar computer-assisted, differential compliance spinal instrument has been developed, and a few studies on it have appeared. [209, 210] This latter device also applies an impulse load (up to ~150 N), although the duration of the impulse has not been characterized in articles available in the indexed peer-reviewed literature. The device also incorporates a sensor to measure the compliance of the material that it loads, and hence, the compliance of the paraspinal region can be assessed as well as loaded with the same device. A case study has reported that the instrument was used to treat the spines of infants having colic. [210] F.   Recommendations and Action Steps Determine (quantify) the biomechanical basis of the subluxation. Determine the parameters that dictate whether a given vertebra should be manipulated. Determine the parameters that will guide the optimal approach to administering the manipulation. Determine the effects of manipulation on tissues of the spine. Which ligaments (including facet joint capsule) sustain the largest strains due to SM The influence of the vector direction of a given type of SM on ligament strains Measure the effects of SM on change in tissue characteristics (eg, ligament modulus of elasticity) and cellular response to SM. Quantify the biomechanical safety of SM in fracture, disk lesions, ligament strains, muscle, and tendon strains. Develop comprehensive models of the spine that predict how it responds to physiologic and SM loads. Determine the biomechanical parameters of SM that dominate the neurophysiologic beneficial effects of SM.

The Effects of Chiropractic Adjusting

NOTE:   All the related articles are listed below this Table.   Jump to Effects articles

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited FROM:   J Manipulative Physiol Ther. 2006 (Nov);   29 (9):   726–761 Biomechanics Biomechanics is the study of the effects of loads applied to biologic cells, tissues or systems. Biomechanics has its origins from Galileo's studies of mechanics in general and his creation of the term mechanics as a subtitle of his book "Two New Sciences" (1638) to refer to force, displacement, and strength of materials. Arguably, the “father of biomechanics” is Giovanni Alfonso Borelli, who published in "De Motu Animalium" (1681) the principles of muscle movements based on statics and dynamics. However, the word “biology” and its concept as the study of living organisms did not occur until 1802 when the German naturalist, Gottfried Reinhold Treviranus, published his first volume "Biologie; oder die Philosophie der lebenden Natur". To rigorously understand SM and its effects requires an understanding of the principles of biomechanics. Manipulation Forces Since the publication of the first white paper in 1997, there have been several important studies that have further clarified the loads that are applied during SM, and especially during high-velocity, low-amplitude (HVLA) SM. Triano and Shultz [150] measured the total force that was transmitted through the body during a side-lying lumbar or lumbosacral HVLA SM. The transmitted forces were similar to the applied forces for their temporal history, but the transmitted forces and moments were shown to vary substantially based on patient positioning. Herzog et al [151] measured the force distribution during thoracic HVLA SM and concluded that there was an important distinction between the total and effective applied forces, with the latter being much smaller than the total applied force. They found that the total peak force was being applied over a mean contact area of 34.8 cm2, but for the thoracic spine, the physiologic contact area of the transverse processes was only 0.25 cm2 (less than 1/100 of the total contact region). Hence, most of the total peak force was being applied to soft tissues (eg, skin, muscle, and fat), and only a small portion (~5 N) was being applied to the transverse process. A similar finding was reported by Kirstukas and Backman, [152] who reported that the “intense contact area” was on the order of 10 cm2 during thoracic HVLA SM. Clearly, the effective applied force during HVLA SM in general will vary based on the contact area of the manipulator's hand and the aspect of the vertebra, but in general, the effective force will be less, and sometimes substantially so, than the applied force. The 3-dimensional force applied during HVLA SM of the cervical, thoracic, and sacroiliac regions has now been measured. [153] The 3-dimensional data showed that forces in plane with the back (ie, Fx and Fy or shearing forces) always occurred during the SM, which was dominated by the normal (ie, Fz or perpendicular) applied force. The shearing forces were considerable in magnitude, ranging from a low mean of 15% (at T4–5) to a high of 29% (at sacroiliac) of the peak Fz force. As has been previously reported by others, [154] there was a consistent drop in the preload force magnitude just before the impulse portion of the HVLA SM, which is speculated to be due to a “countermovement” affect. The role of sex in developing force magnitude has been investigated. [155] The only previous report that compared male and female manipulators found no significant differences during HVLA SM using a patient simulator. [156] Forand et al [155] used an experienced matched group (range, 1–24.5 year of experience) of female and male chiropractors (14 per group) and found that there were no significant differences between sexes in thoracic HVLA SM forces. The one exception was that, in the lower thoracic spine, men applied significantly greater preload than did women. Another type of SM is mobilization or low-velocity low-amplitude SM, which is commonly used by physical therapists as well as other health professionals, including chiropractors. The general approach is to apply an increasing force over 5 to 10 seconds to determine the “end feel,” and then so calibrated, to apply a slow oscillation (~1 Hz for 10 seconds) about a mean graded force (I–IV arbitrary scale), which is less than the end feel. [157] Using an instrumented mobilization table, it was found that there was considerable variation in the force magnitudes used by experienced therapists for end feel, as well as grades I–IV mobilizations of L3 vertebra in healthy subjects. [157] When comparing treatment of younger vs older healthy subjects, it was found that, although mean forces were similar, smaller amplitudes and higher frequency of oscillations were used with older patients. [158] In a study of patients with nonspecific low back pain, there was considerable variation in the magnitudes of forces used, but the variation was strongly influenced not by the patient's severity of complaint but by the physical therapist's training. [159] Effects of External Loading on Vertebral Displacements Our understanding of the kinematics of SM has been increased by 2 different types of investigations. First, Keller et al [160–162], have published 2 studies using mechanical force, manually assisted, short-lever SM (ie, Activator [Activator Methods International, Phoenix, Ariz] or very HVLA [VHVLA]) in vivo on patients undergoing lumbar surgery. Using forces ranging from 30 N (lowest setting) to 150 N (maximum setting) on the adjusting instrument, the vertebra where the force was applied had peak displacements of approximately 0.5 mm occurring within 10 milliseconds. Intersegmental displacements occurred of similar magnitudes but with large oscillations lasting 2 to 3 times longer (ie, 20–30 milliseconds), but all oscillations appeared to have damped out within 100 milliseconds. In a second in vivo study, they found that the vertebral displacements due to the Activator instrument were slightly larger (mean, ~0.62 mm) and did not vary significantly, depending on whether the instrument was positioned over the spinous process or facet joint (left or right). [163] 0 Second, using intact cadaveric human lumbar spine specimens, Ianuzzi and Khalsa [164] simulated lumbar HVLA SM while measuring vertebra kinematics and facet joint capsule strain. During simulated HVLA SM, the applied loads were within the range measured during in vivo HVLA SM. Vertebral translations occurred primarily in the direction of the applied load and were similar in magnitude (on order of 1–2 mm) regardless of manipulation site. Vertebral rotations (on order of 1°–3°) and facet joint capsule strain magnitudes (on order of 5%) during simulated HVLA SM were within the range that occurred during physiologic motions. [165] At a given facet joint capsule, distal manipulations induced capsule strains similar in magnitude to those that occurred when the manipulation was applied proximally. The mobility of lumbar vertebrae in healthy volunteers during mobilization has been assessed using dynamic MRI. Powers et al [166] found that applying a 10-second grade IV posterior to anterior (PA) mobilization (~100 N force) at the spinous process of a lumbar vertebra produced an extension of the vertebra ranging from a mean of 1.2° at L2 to 3.0° at L5. Using plain film radiographs, Lee and Evans [167] found similar displacements for a 150 N PA mobilization at L4. Kulig et al, [168] also using dynamic MRI, found that applying a PA mobilization induced intersegmental motion in all lumbar vertebrae, caudal and cranial, to the site of applied force. This is consistent with the findings of Ianuzzi and Khalsa [164] who also found that simulated HVLA SM at a single vertebra induced motion in all other lumbar vertebrae. Thus, it is not possible to move only a single vertebrae with SM (high or low velocity) because the spine is a linked and coupled structure. Other effects HVLA SM is commonly associated with a “cracking” sound, which has previously been shown to be associated with a cavitation phenomenon in the facet joints. [169, 170] In healthy volunteers, Ross et al [171] found that single HVLA SM were typically associated with multiple cavitations (ranging from 2 to 6), which were from nearby vertebrae. This was consistent with the findings of Beffa and Mathews, [172] who found no significant relationship between the location of the cavitation and HVLA SM of the L5 or sacroiliac joint in asymptomatic volunteers. There is some question as to whether HVLA SM can actually induce motion into the sacroiliac joint, as Tullberg et al, [173] using stereo radiography, were unable to measure any significant motion of the sacrum relative to the ilium after a combination of HVLA and mobilization SM in patients with “subluxated” sacroiliac joints. Furthermore, Flynn et al [174] found no association between an “audible pop” and improvement in ROM, pain, or disability in patients with nonradicular low back pain. Measures of Pathologic States An intriguing question has begun to be answered relating to whether changes in intersegmental stiffness can be discerned using clinically available tools. Colloca et al [175] measured intersegmental impedance (dynamic stiffness) of lumbar vertebrae and correlated it with characteristics of vertebral height and IVD height measured from plain film radiographs. They found that there was a correlation between decreased disk height at L5–S1 and increased dynamic stiffness at the same segment. These findings were analogous to those of Kaigle et al [176] who, using a porcine model, also observed increased spine dynamic stiffness associated with degenerated disks, compared with normal controls. Using ultrasound indentation, another noninvasive approach, Kawchuk et al [177] also found that IVD degeneration in a porcine model resulted in decreased indentation for the same applied load. This is an analogous metric as spine stiffness. The use of ultrasound indentation in this animal model had high sensitivity (75.0%), specificity (83.3%), and accuracy (77.1%), compared with other approaches (arthroscopy, MRI, and plain film radiography). Two biomechanics studies have been performed to examine the effects of fixation (ie, a hypomobile subluxation) of the lumbar spine. Cramer et al [13] used a rat model of fixation in the lumbar spine by externally fixating the spinous processes of L4–L6 for up to 8 weeks. A principal finding due to the fixation was the development of osteophytes and degenerative articular changes of the facet joints within a few weeks. Reversal of some of the degeneration was observed for joints that were fixated for a short term (~1 week), but after 4 weeks, no reversal was observed. Little et al [178] simulated a hypomobile subluxation in intact, cadaveric human lumbar spine specimens by screwing a plate into the left anterior aspect of the L4 and L5 vertebral bodies. During physiologic motions of the fixated spine specimens for flexion, extension, and lateral bending, the motions at L4–5 were significantly decreased, whereas below and above that level, intersegmental motions were significantly increased. Correspondingly, the plane strains of the facet joint capsules were significantly decreased and increased at and above/below the site of fixation, respectively. Diagnostic tools or outcome measures The principal biomechanical “tool” still used by most chiropractors is palpation. As such, there has been a continued investigation into factors that change what is felt during palpation. Humans are relatively good at discriminating different magnitudes of stiffness for purely “elastic” materials. [179] However, the human spine responds as a viscoelastic system, in which the speed of force application changes the apparent stiffness. Nicholson et al [180] have shown that the relatively poor ability of clinicians to accurately estimate spine stiffness magnitudes is likely due to a 50% poorer ability to discriminate viscous components of viscoelastic systems. Latimer et al [181] found that therapists used different forces to discern spine stiffness and, hence, had different internal perceptual scales. By training therapists to use a calibrated stiffness instrument, discrimination of PA stiffness in the spine can be done with relatively high interexaminer reliability. [182] Furthermore, objective instruments have been developed that can reliably measure PA spine stiffness. [183] Perhaps, the most important aspect of using palpation to detect subluxations (ie, a “manipulable lesion”) is standardization of training. [184] When examiners are trained in a standardized fashion, they are able to obtain relatively high interexaminer reliability (? = 0.68) for detecting cervical fixations. Stiffness of the spine is influenced by many factors. If the ribcage is constrained, then the stiffness measured at T12–L4 can be significantly increased. [185] Change in orientation of an applied load to the spinous process can have small yet significant changes in objectively measured stiffness. [186] Furthermore, because the spine is a viscoelastic system, there will be a preconditioning effect when applying loads, such that after preconditioning the spine with standard mobilization SM, there will be no measurable change in stiffness. [187] There has also begun to be a growing appreciation for the natural (and normal) variability in spine stiffness as assessed by standard ROM tests during a physical examination. Christensen and Nilsson [87] found that in asymptomatic volunteers during a 3-week period, there was an intrinsic variability in ROM of the cervical spine of ± 20°, ± 14°, and ± 12° for flexion/extension, lateral bending, and rotation, respectively. In contrast, repositioning the head to the neutral position, which is related to proprioception, is done with relatively high fidelity over the same period. [188] Asymptomatic volunteers were able to reachieve the neutral zero position of their heads with a mean difference of 2.7°, 1.0°, and 0.7° for the sagittal, horizontal, and frontal planes, respectively. Using a case study approach, Lehman and McGill [189] observed that a single HVLA SM session in the lumbar spine caused notable changes in biomechanical factors associated with a complex task (ie, a golf swing in an experienced golfer who had chronic low back pain). In addition to changes in vertebral kinematics, they observed decreased electromyographic (EMG) responses of the associated lumbar muscles. In a subsequent study, Lehman and McGill [190] found that lumbar HVLA SM in patients with low back pain resulted in variable changes in lumbar ROM and associated muscle EMG. The largest changes were associated with patients with the greatest reported pain. In a review of the available literature. Lehman [191] reported that, currently, the best way to discriminate between normal and low back patient groups was using biomechanical tests that assessed “higher-order kinematics during complex movement tasks.” Simpler end ROM tests had poor predictive ability. Another commonly performed clinical test is measuring leg lengths, especially in the prone position. Using a special designed table to minimize friction and allow independent loading of each leg, Jansen and Cooperstein [192] determined that the prone leg length test was reliable for detecting non–weight-bearing asymmetry in leg lengths. Nguyen et al [193] found that there was reasonable concordance (? = 0.6) in determining whether a short leg was present using the Activator protocol. Cooperstein et al [194] found that it was possible to detect a leg length difference of 1.9 mm but recommended that only differences of greater than 3.7 mm should have confidence associated with them. Mathematical and Computational Models One of the signs of maturity of any field is the ability to produce predictive models. In spine biomechanics, most models are computationally based and either use finite element approaches [195] or optimization with minimization of an objective function. Analytical approaches have also been performed, which include a linear elastic model of a lumbar motion segment. [196] This model successfully predicted loads born by various ligaments under physiologic loads. Solinger [197] created a model that predicted the dynamic response of L2–L3 to impulsive loads on the order of those used in VHVLA SM. Using a lumped parameter approach, Keller and Colloca [198] created an analytical model that predicted the frequency dependent response of the human lumbar spine to PA forces applied to the spinous processes, as is done during low velocity and low amplitude (ie, mobilization), HVLA, and VHVLA (ie, Activator). An alternative approach was adopted by Dulhunty [199] who modeled force transmission in the cervical spine to predict whether parallel forces or concurrent forces are the optimization function. A relatively new approach in spine modeling, especially in the lumbar spine, is to incorporate what are called “follower loads” for muscles. The issue is that the ex vivo (cadaveric) intact lumbar spine will buckle under compressive loads of ~100 N, whereas in vivo, the lumbar spine easily supports compressive loads of ~1000 N (ie, 10 times greater). Patwardhan et al [200] found that by modeling muscle activation so that their loads followed the tangent of the lumbar lordosis, their model would approximate the in vivo condition. A couple of new comprehensive models have been advanced to explain how the spine becomes subluxated in the first place and how SM can restore it to “normal.” Triano [201, 202] has advocated a mechanical model based on the concept of intersegmental buckling, which was based on original observations by Wilder et al [203, 204] and fluoroscopic recordings of a buckling event in a weightlifter by Cholewicki et al [205] and Cholewicki and McGill. [206] Essentially, this model proposes that there is a balance point between each pair of vertebrae that under certain loading conditions can suddenly shift, which then results in increased tissue strain of associated soft tissues (eg, facet joint capsule). The increased tissue strain can result in small tears and associated biologic inflammatory response. Evans et al [207] have proposed an optimization model where the spine system is biased toward minimizing the mechanical energy associated with loading the spine. Their model is described for the case of linear elasticity, although they claim it is also apropos of nonlinear elasticity. As with any theory (or model), the value of these new theories is really found in their predictive ability and how well their predictions are validated by experimental data. So far, neither of these theories has been tested to any degree. Instrumented Manipulation Passive devices have been used for many decades to treat patients with back disorders. Recently, a simple distraction device, Rola Stretcher (Unique Relief, Inc, Davenport, Iowa), designed to be used at home without supervision, was tested to determine whether it showed any lengthening of the spine subsequent to its use. Devocht et al [208] tested 12 asymptomatic adults and found a significant increase in sitting height after 10 minutes of lying supine on the device. They concluded that it at least temporarily lengthened the spine, presumably by increasing the intervertebral disk height. In addition to the activator adjusting tool, which has had increasing amounts of scientific study, [160–163] the PulStar computer-assisted, differential compliance spinal instrument has been developed, and a few studies on it have appeared. [209, 210] This latter device also applies an impulse load (up to ~150 N), although the duration of the impulse has not been characterized in articles available in the indexed peer-reviewed literature. The device also incorporates a sensor to measure the compliance of the material that it loads, and hence, the compliance of the paraspinal region can be assessed as well as loaded with the same device. A case study has reported that the instrument was used to treat the spines of infants having colic. [210] F.   Recommendations and Action Steps Determine (quantify) the biomechanical basis of the subluxation. Determine the parameters that dictate whether a given vertebra should be manipulated. Determine the parameters that will guide the optimal approach to administering the manipulation. Determine the effects of manipulation on tissues of the spine. Which ligaments (including facet joint capsule) sustain the largest strains due to SM The influence of the vector direction of a given type of SM on ligament strains Measure the effects of SM on change in tissue characteristics (eg, ligament modulus of elasticity) and cellular response to SM. Quantify the biomechanical safety of SM in fracture, disk lesions, ligament strains, muscle, and tendon strains. Develop comprehensive models of the spine that predict how it responds to physiologic and SM loads. Determine the biomechanical parameters of SM that dominate the neurophysiologic beneficial effects of SM.

The Effects of Chiropractic Adjusting

	Subluxation–based Guidelines A Chiro.Org article collection Please review this collection of treatment guidelines from the International Chiropractors Association (ICA) and the Council on Chiropractic Practice (CCP).
	The About Chiropractic Adjusting Page A Chiro.Org article collection Review a variety of articles about chiropractic adjusting (aka spinal manipulation).
	The Cost-Effectiveness of Chiropractic Page A Chiro.Org article collection These studies suggest that spinal adjusting (or manipulation if you prefer) and chiropractic management is both highly effective and cost-effective in comparison to standard medical management for neck and low back pain and for headaches.
	The Patient Satisfaction With Chiropractic Page A Chiro.Org article collection These studies reveal that chiropractic care is much more popular with patients than standard medical management for neck and low back pain, or for headaches.
	Elevated Production of Nociceptive CC-chemokines and sE-selectin in Patients with Low Back Pain and the Effects of Spinal Manipulation: A Non-randomized Clinical Trial Clin J Pain. 2018 (Jan); 34 (1): 68–75 ~ FULL TEXT The production of chemotactic cytokines is significantly and protractedly elevated in LBP patients. Changes in chemokine production levels, which might be related to SMT, differ in the acute and chronic LBP patient cohorts.
	Attenuation Effect of Spinal Manipulation on Neuropathic and Postoperative Pain Through Activating Endogenous Anti-Inflammatory Cytokine Interleukin 10 in Rat Spinal Cord J Manipulative Physiol Ther 2016 (Jan); 39 (1): 42–53 Our results showed that repetitive ASMT significantly suppressed neuropathic pain after CCD and the postoperative pain after de-CCD, reduced the increased excitability of CCD and de-CCD DRG neurons, attenuated the DRG inflammation, and inhibited induction of c-Fos and expression of PKC in the spinal dorsal horn. Most interestingly, ASMT significantly increased level of the anti-inflammatory cytokine IL-10 in the spinal cord and reduced level of IL-1? in DRG in CCD and de-CCD rats. These results suggest that ASMT may attenuate neuropathic pain through, at least partly, activating the endogenous anti-inflammatory cytokines IL-10.
	Neural Response During a Mechanically Assisted Spinal Manipulation in an Animal Model: A Pilot Study J Nov Physiother Phys Rehabil. 2015 (Sep);   2 (2):   20–27 ~ FULL TEXT This pilot study demonstrates feasibility of recording in vivo muscle spindle response during spinal manipulation using clinical mechanically-assisted spinal manipulation devices. It also demonstrates that extremely short duration manipulative thrusts (<5ms) of equivalent forces to that delivered to the human cervical spine can have an immediate and/or perhaps a prolonged effect (> 40s) on paraspinal muscle spindle discharge. While the clinical relevance of how mechanoreceptor stimulation or inhibition related to spinal manipulation modulates central nervous system activity remains to be clarified, determining how various mechanoreceptors respond during and following spinal manipulative thrusts in a clinically relevant fashion is an important step toward achieving this goal.
	Does Inter-vertebral Range of Motion Increase After Spinal Manipulation? A Prospective Cohort Study Chiropractic & Manual Therapies 2014 (Jul 1); 22: 24 ~ FULL TEXT Of importance is the finding that sagittal plane hypomobile segments were not significantly more prevalent in patients than in controls, casting doubt on the relevance of sagittal plane hypomobility in patients with relatively mild non-specific neck pain. However, this may not be the case in other populations and planes of motion. Indeed, such hypomobility may be of importance only in a subgroup of neck patients.
	Biomechancial Quantification of Pathologic Manipulable Spinal Lesions: An In Vivo Ovine Model of Spondylolysis and Intervertebral Disc Degeneration J Manipulative Physiol Ther 2012 (Jun); 35 (5): 354–366 ~ FULL TEXT Using a previously validated ovine lumbar degenerative disc lesion model and a novel ovine spondylolysis lesion model, surgically induced spinal lesions were prospectively tracked histologically and radiologically through a 6-month follow-up. Objective evidence of an increase in dynamic spinal stiffness, as well as reductions in vertebral displacements occurring in response to SM, were observed in the spondylolysis and disc degeneration groups compared with their age-matched and exposure level controls. Histologic evidence of pathology consistent with an alteration of spinal stiffness accompanied by alterations in the neuromuscular system provides novel insights into quantifying manipulable spinal lesions as well as a means to biomechanically assess SMT outcomes.
	Cerebral Perfusion in Patients with Chronic Neck and Upper Back Pain: Preliminary Observations J Manipulative Physiol Ther. 2012 (Feb); 35 (2): 76–85 ~ FULL TEXT Group 1 (mild) consisted of 14 patients. Cerebral perfusion measured by SPECT was normal in all 8 brain regions. Group 2 (moderate) consisted of 16 patients. In this group, a decrease in cerebral perfusion was observed (range, 20%–35%), predominantly in the parietal and frontal zones. Group 3 (severe) consisted of 15 patients. In this group, the decrease in cerebral perfusion observed was from 30% to 45%, again predominantly in the parietal and frontal zones.   A significant difference was found between NDI groups ("moderate" and "severe" showed significantly greater hypoperfusion than "mild").   Total blockage score correlated with SPECT scores at r = 0.47, P = .001. In a multivariate analysis, NDI scores contributed 39% of the variance of SPECT scores.
	Cerebral Metabolic Changes in Men After Chiropractic Spinal Manipulation for Neck Pain Altern Ther Health Med. 2011 (Nov); 17 (6): 12–17 ~ FULL TEXT Research on chiropractic spinal manipulation (CSM) has been conducted extensively worldwide, and its efficacy on musculoskeletal symptoms has been well documented. Previous studies have documented potential relationships between spinal dysfunction and the autonomic nervous system and that chiropractic treatment affects the autonomic nervous system. The authors hypothesized that CSM might induce metabolic changes in brain regions associated with autonomic nervous system functions as assessed with positron emission tomography (PET). PET is a nuclear medicine imaging technique that allows quantification of cellular and molecular processes in humans such as cerebral glucose metabolism which is thought to reflect regional neuronal activities.
	Elevated Production of Inflammatory Mediators Including Nociceptive Chemokines in Patients With Neck Pain: A Cross-Sectional Evaluation J Manipulative Physiol Ther. 2011 (Oct); 34 (8): 498–505 ~ FULL TEXT Production of inflammatory mediators was consistently elevated in NP patients in this study, both in vitro and in vivo, and activation of inflammatory pathways was accompanied by up-regulation of CC chemokine synthesis. This suggests that, in NP patients, CC chemokines may be involved in regulation of local inflammatory response through recruitment of immune cells to the inflamed tissue and exert pronociceptive effects.
	Subclinical Neck Pain and the Effects of Cervical Manipulation on Elbow Joint Position Sense J Manipulative Physiol Ther. 2011 (Feb); 34 (2): 88–97 ~ FULL TEXT These results suggest that asymptomatic people with a history of subclinical neck pain (SCNP) have reduced elbow JPS accuracy compared to those with no history of any neck complaints. Furthermore, the results suggest that adjusting dysfunctional cervical segments in people with SCNP can improve their upper limb JPS accuracy.
	Increased Multiaxial Lumbar Motion Responses During Multiple-Impulse Mechanical Force Manually Assisted Spinal Manipulation Chiropractic & Osteopathy 2006 (Apr 6);   14 (1):   6 ~ FULL TEXT Knowledge of the vertebral motion responses produced by impulse-type, instrument-based adjusting instruments provide biomechanical benchmarks that support the clinical rationale for patient treatment. Our results indicate that impulse-type adjusting instruments that deliver multiple impulse SMTs significantly increase multi-axial spinal motion. There are more articles like this at our Instrument Adjusting Page.
	The Efficiency of Multiple Impulse Therapy for Musculoskeletal Complaints J Manipulative Physiol Ther 2006 (Feb);   29 (2):   162 ~ FULL TEXT Response of patients in the study sample to multiple impulse therapy for symptoms of low back and neck pain appeared to be considerably faster than that obtained in 3 recent studies.
	Self-reported Nonmusculoskeletal Responses to Chiropractic Intervention: A Multination Survey J Manipulative Physiol Ther 2005 (Jun); 28 (5): 294–302 ~ FULL TEXT Positive reactions were reported by 2% to 10% of all patients and by 3% to 27% of those who reported to have such problems. Most common were improved breathing (27%), digestion (26%), and circulation (21%).
	Areas of Capsaicin-Induced Secondary Hyperalgesia and Allodynia Are Reduced by a Single Chiropractic Adjustment: A Preliminary Study J Manipulative Physiol Ther. 2004 (Jul); 27 (6): 381–387 ~ FULL TEXT The results confirmed that topical capsaicin induced inflammatory reactions based on occurrence of hyperalgesia and allodynia, augmented pain perception, and increased blood flow following capsaicin application compared with the control session. When compared with N-SMT, spontaneous pain was rated significantly lower post-SMT (P <.014). In addition, areas of both secondary hyperalgesia and allodynia decreased after SMT (hyperalgesia: P <.007; allodynia: P <.003). However, there was no significant treatment effect for local blood flow.   These results suggest hypoalgesic effects following a single SMT. As local vascular parameter was not affected by the single SMT, the hypoalgesic effects appear to be due to central mechanisms.
	Effect of Chiropractic Treatment on the Endocrine and Immune System in Asthmatic Patients Proceedings of the 2002 International Conference on Spinal Manipulation The broad aims of this FCER funded study is to determine whether stress is a factor in the pathophysiology of asthma and to determine if chiropractic management of asthmatics can alleviate stress induced asthma. More specifically for this meeting, our study aims to determine whether chiropractic treatment has beneficial effects on the endocrine system through measurement of salivary cortisol and on the immune system via salivary IgA determination. You can review other articles on this topic at the Chiropractic and Asthma Page.
	Chronic Pediatric Asthma and Chiropractic Spinal Manipulation: A Prospective Clinical Series and Randomized Clinical Pilot Study J Manipulative Physiol Ther 2001 (Jul); 24 (6): 369–377 ~ FULL TEXT After 3 months of combining chiropractic SMT with optimal medical management for pediatric asthma, the children rated their quality of life substantially higher and their asthma severity substantially lower. These improvements were maintained at the 1-year follow-up assessment.
	Epilepsy and Seizure Disorders: A Review of Literature Relative to Chiropractic Care of Children J Manipulative Physiol Ther 2001 ( Mar); 24 (3): 199–205 ~ FULL TEXT Chiropractic care may represent a nonpharmaceutical health care approach for pediatric epileptic patients. Current anecdotal evidence suggests that correction of upper cervical vertebral subluxation complex might be most beneficial. It is suggested that chiropractic care be further investigated regarding its role in the overall health care management of pediatric epileptic patients.
	The Short–Term Effect of Spinal Manipulation in the Treatment of Infantile Colic: A Randomized Controlled Clinical Trial with a Blinded Observer J Manipulative Physiol Ther 1999 (Oct); 22 (8): 517–522 ~ FULL TEXT By trial days 4 to 7, hours of crying were reduced by 1 hour in the dimethicone group compared with 2.4 hours in the manipulation group (P = .04). On days 8 through 11, crying was reduced by 1 hour for the dimethicone group, whereas crying in the manipulation group was reduced by 2.7 hours (P = .004). From trial day 5 onward the manipulation group did significantly better that the dimethicone group. The authors then conclude: Spinal manipulation is effective in relieving infantile colic.   You will also enjoy FCER's review of this article.
	Endometriosis and the Anterior Coccyx: Observations on 5 Cases Research Forum 1985 (Summer); 1 (4): 120–122 ~ FULL TEXT This case review involves five women presenting with medically-diagnosed endometriosis. All five women had been advised that they were surgical candidates. Relief of symptoms is effected by adjusting the anteriorally displaced coccyx. The author suggests a relationship between the displaced coccyx and endometriosis and counsels upon the recognition of same.

The Evolution of the Subluxation Theory

	Radiologic Manifestations of Spinal Subluxations Chapter 6 from:   “Basic Chiropractic Procedural Manual” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter describes the radiologic signs that may be expected when spinal subluxations are demonstrable by radiography. Through the years, there have been several concepts within the chiropractic profession about what actually constitutes a subluxation. Each has had its rationale (anatomical, neurologic, or kinematic), and each has had certain validity contributing to our understanding of this complex phenomenon.
	General Causes and Potential Effects of the Subluxation Complex Chapter 6 from:   “Basic Principles of Chiropractic Neuroscience” By Richard C. Schafer, D.C., FICC and the ACAPress Until the last 2 decades, most evidence about the success of chiropractic adjustments on the correction of vertebral subluxations and their related functional disturbances was empiric. The gap between controlled research documentation and frequent clinical observation still exists, but it has greatly narrowed in recent years. The greatest concern today is not is it effective but why is it effective and why is it effective in some cases but not in others that appear almost identical? Added to these can be the questions: what causes the positive effects in a specific body area that result from spinal adjustments that cannot be explained on an anatomical basis and what causes the indirect, far-reaching, diverse improvement in function so often witnessed?
	Specific Potentialities of the Subluxation Complex Chapter 7 from:   “Basic Principles of Chiropractic Neuroscience” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter describes the primary neurologic implications of subluxation syndromes, either as a primary factor or secondary to trauma or pathology, within the cervical spine, thoracic spine, lumbar spine, and pelvic articulations.
	Basic Spinal Subluxation Considerations Chapter 19 from:   “Chiropractic Management of Sports and Recreational Injuries” By Richard C. Schafer, D.C., FICC and the ACAPress The concept that an "off centered" vertebral or pelvic segment parallels a unique effect upon the neuromuscular bed which may be the cause of, aggravation of, or "triggering" of certain syndromes is a major contribution to the field of functional pathology and clinical biology by the chiropractic profession. This section discusses the basic biomechanics and effects of vertebral subluxations as related to the management of sports-related and recreational injuries.
	Chiropractic Lexicon: Useful or Not? Asia Pacific Chiropractic Journal 2023; 3.3 ~ FULL TEXT Obtaining an ultimate definition of this ‘something’ we have been addressing, successfully, for over 125 years is elusive, yet this allows flexibility when defining it within different contexts. This provides space for chiropractors to do this (both consciously and subconsciously) every day in practice, and over time to use their growing experience to add complexity and subtlety to their conceptual framework, and their application of their science and art. Millions of patients over the years would attest to the value in that.
	The Chiropractic Subluxation: Medical Evidence in Support of the Subluxation Construct Asia Pacific Chiropractic Journal 2023; 3.3 ~ FULL TEXT The vertebral subluxation concept is similar to the terms spinal dysfunction, somatic dysfunction, segmental dysfunction or the vague vertebral lesion. These terms are primarily used by osteopaths, physiotherapists and medical doctors to focus their manipulative techniques, but they relate primarily to the physical-mechanical aspects. In this respect, these terms are limited in what they signify. The implication of just plain osseous biomechanical dysfunction does not incorporate the wider ramifications of integrated neural, vascular, and internal associations which may involve greater ramifications, and should be more appropriately referred to as a vertebral subluxation complex (VSC).
	The Chiropractic Vertebral Subluxation Part 10: Integrative and Critical Literature From 1996 and 1997 J Chiropractic Humanities 2018 (Dec); 25: 146–168 ~ FULL TEXT The purpose of this paper is to review and discuss the history of chiropractic vertebral subluxation (CVS) during 1996 and 1997. The literature during this period offered critical and integrative models emphasized by a need for research into operational and functional definitions. Several integrative approaches emerged, from Rome’s 296 synonyms to Bergman’s Pain/Tenderness, Asymmetry/Alignment, Range of Motion Abnormality, Tissue Tone, Texture, Temperature Abnormality, and Special Tests (PARTS) analysis adopted by the profession in the United States. Other noteworthy contributions included Ruch’s Atlas of Common Subluxations, Epstein’s introduction of network spinal analysis, and Kent’s review of CVS models. Boone’s introduction of the J Vertebral Subluxation Research was accompanied by his 3-part model with Dobson. These years also included the paradigm statement of the Association of Chiropractic Colleges, which was adopted by the American Chiropractic Association, International Chiropractors Association, and World Federation of Chiropractic. Two other papers included Nelson’s critique of the CVS paradigm and Keating’s 1996 “Hunt for the Subluxation.” You may also enjoy The Chiropractic Vertebral Subluxation: Parts 1–9
	The Chiropractic Subluxation: Implications for Manual Medicine J Manual & Manipulative Therapy 2016; 13 (3): 139–141 ~ FULL TEXT But perhaps the greatest lesson to be learned here is a caveat. Nobody benefits if we spend too much time on constructing theoretical models with poor operational definitions and hidden elements of dogmatic thinking. Maybe it is time to critically evaluate the diagnostic value of clinically unquantifiable manual medicine concepts such as endfeel. Maybe it is time to question clinical but unproven constructs such as the capsular pattern and its diagnostic and therapeutic implications. Maybe it is time to clearly and quantifiably define what we consider a positive finding on our tests of segmental motion and stability. Or maybe it is time to discard the unproven emphasis we place on these poorly operationalized segmental tests. Instead, we could focus our efforts on establishing clinical decision rules for manipulative interventions using tests with a clear operational definition while at the same time establishing outcomes with reliable, valid, and responsive outcome tools that can be used by any practitioner unrelated to their level of experience. Maybe it is time to demystify manual medicine as an approach only for the duly initiated and let it truly enter the era of evidence-based medicine?
	Use of the Term Subluxation in Publications During the Formative Years of the Chiropractic Profession J Chiropractic Humanities 2011 (Dec); 18 (1): 1–9 The term subluxation has come to have different meanings for different health care professions in the United States for over the past century. This controversy has resulted in some contention both internal and external to the chiropractic profession. Some current factions within the chiropractic profession hold the term subluxation to be synonymous with the identity of chiropractic itself; however, this term was not solely used by chiropractic during its formative years. The purpose of this article is to look at uses of the term by various professions (osteopathy, medicine, and chiropractic) at the turn of the century, a time in which the chiropractic profession was developing.
	The Great Subluxation Debate: A Centrist's Perspective J Chiropractic Humanities 2010 (Jun); 17 (1): 33–39 ~ FULL TEXT The long-standing debate regarding the chiropractic subluxation has created substantial controversy within the profession. Currently, this phenomenon can be compared with a country with a 2-party system that has a large silent majority sitting between the 2 factions. It is argued that the position held by those in the middle (the centrists) may be the most rational view when considering all of the available evidence. It is also suggested that the subluxation construct is similar to the Santa Claus construct in that both have a factual basis as well as social utility.   Ultimately, the centrists must become proactive if they want to protect the profession and further advance the evidence in regard to the subluxation. They must not only engage in the debate, but fund the research that will investigate various aspects of the subluxation and then help disseminate this evidence to fellow doctors of chiropractic, other practitioners, health care policy makers, and society at large.
	Subluxation Reviewed, Revisited, Revitalized Dynamic Chiropractic (March 12, 2010) ~ FULL TEXT Our understanding of the biomechanics and neurology of the subluxation continues to evolve as more research is published which helps explain the nature of this lesion. Historically, the subluxation has been at the heart of the identity and purpose of the chiropractic profession. Contemporary models provide new insights into this elusive and sometimes mysterious problem which we attempt to find by various clinical means and correct by the application of high-velocity, low-amplitude thrusts. Let's review past models, but focus primarily on the latest evidence concerning the subluxation published in the recent scientific literature in order to improve our understanding, insight, and application of clinical interventions to improve patient outcomes with chiropractic care.
	Neurovertebral Influence Upon the Autonomic Nervous System: Some of the Somato-Autonomic Evidence to Date Chiropractic Journal of Australia 2009 (Mar); 39 (1): 2–17 ~ FULL TEXT The volume and variety of evidence presented in this cursory overview, would tend to suggest there should be open mindedness when considering the possibilities of manual management of a number of somatovisceral conditions. An attitude of outright rejection may tend to limit chiropractic within a musculoskeletal field. This could deny science a whole area of opportunity, and deprive certain patients of options for a potential source of minimally invasive natural health management. Once all the available evidence is considered, and further research has had the opportunity to explain the clinically observed phenomenon of positive outcomes, proper assessment can then take place. Despite the material presented here, one is still reticent in making broad claims..
	Survey of US Chiropractor Attitudes and Behaviors about Subluxation J Chiropractic Humanities 2008; 15 (1): 19–26 ~ FULL TEXT Comprehensive, biopsychosocial approaches to care of the chiropractic patient have added utility for addressing a multitude of complex multi-causal health disorders. Our survey findings lend support to the notion that the typical doctor of chiropractic is not a simplistic ideologue in their clinical approach. Rather, our findings support and we respect the suggestion that contemporary practicing chiropractors are capable of reconciling complex notions of health, well-being, and dysfunction, by tailoring specific care for specific disorders in specific patients. [11] An agenda for further advancing chiropractic as a clinical discipline and chiropractic as a valued health care choice should also include attention to developing more fully all clinical skill sets that are requisite to successful delivery of a comprehensive biopsychosocial approach to health care.
	Chiropractic Theory in Research: Subluxation Theory Finally Gets the Attention It Deserves Dynamic Chiropractic (April 16, 2006) Theories are designed to explain observable phenomena. In actuality, the "subluxation model" that postulates a relationship between body structure, physiological function and health is an inherently viable one. The precise biomechanical, neurophysiological and/or psychosocial mechanisms that may or may not come into play remain to be elucidated through research. As more becomes known, chiropractic models should rightly be refined to better explain clinical observations. Well-developed theories help pose research questions and study designs that do a better job at finding out information that can improve our practices and benefit the patients we are here to serve.

A Series of Subluxation Articles By Meridel I. Gatterman, MA, DC, MEd Thanks to Dynamic Chiropractic!    The Vertebral Subluxation Syndrome    Is the Spinal Subluxation a Risk Factor?    Separated by a Common Language: Its Time to Develop Chiropractic Nomenclature

	Dump Subluxation? Give Me a Break! Dynamic Chiropractic ~ November 1, 1999 The front-page headline of the September issue (volume 13, no. 12) of the Chiropractic Journal reads "Research Conference Urges Profession to Dump Subluxation." Well, I'm here to tell you that nothing even remotely of the kind happened, and I still find it hard to understand why one person, Matthew McCoy, chose to spin the story so inaccurately, especially after (silently) sitting through only one morning of an extensive three-day meeting at my invitation (and Palmer's expense). A responsible journalist who didn't hear the whole story would have checked not only his facts, but his context as well.
	Models of Vertebral Subluxation: A Review Journal of Vertebral Subluxation Research 1996; 1 (1): 1–6 ~ FULL TEXT Enjoy this Adobe Acrobat file (59 KB) from the first issue of JVSR, a review of clinical models of the vertebral subluxation, including neurobiological mechanisms. Models reviewed include the subluxation complex model, subluxation degeneration, nerve compression, dysafferentation, the neurodystrophic model and segmental facilitation. Clinical models, including the segmental, postural, and tonal approaches are discussed.
	A Review of the Evolution of Chiropractic Concepts of Subluxation Topics in Clincial Chiropractic 1995: 2 (2): 1–10 ~ FULL TEXT This particular review traces the evolution of the subluxation concept within the context of the chiropractic profession. There is a growing body of evidence, from both within and outside the discipline, that supports many of chiropractic's basic concepts. Evidence regarding the contribution of spinal joint derangement to a number of significant health problems becomes more compelling as more is learned. The role of manual procedures, especially as performed by chiropractors, becomes more prominent each year. A new environment without the overt ostracism of political medicine and a burgeoning research enterprise within chiropractic academia and practice are helping to poise the profession for greater contributions to the health care of society as chiropractic enters its next century.

A Series of Subluxation Articles By Joseph M. Flesia, Jr., D.C. Thanks to the ICA for access to these articles!    The Vertebral Subluxation Complex: An Integrative Perspective        ICA Int Rev Chiro 1992 (Mar):   25–27 ~ FULL TEXT    The Vertebral Subluxation Complex Part II: An Outline        ICA Int Rev Chiro 1992 (Oct): 19–23 ~ FULL TEXT    The Vertebral Subluxation Complex Part III: Pathogenesis        ICA Int Rev Chiro 1992 (Oct): 45–47 ~ FULL TEXT    The Vertebral Subluxation Complex Part IV: Pathogenesis (Continued)        ICA Int Rev Chiro 1993 (Mar): 37–41 ~ FULL TEXT

	The Vertebral Subluxation Complex Part 2: The Neuropathological and Myopathological Components Chiropractic Research Journal 1990; 1 (4): 19–38 ~ FULL TEXT The neurological component of the Vertebral Subluxation Complex (VSC) is, for many, the cornerstone of chiropractic theory. [1] For those who see beyond the application of chiropractic and other manipulative procedures as merely a means of relieving head ache and low back pain, the nervous system is the mediator of vitality and health to the individual organs and tissues. [2] Today, more than ever before, basic scientific and medical research supports this fundamental concept of chiropractic. [3–7] In chiropractic clinical practice, the prominence of the nervous system is unquestionable.
	The Vertebral Subluxation Complex Part 1: An Introduction to the Model and Kinesiological Component Chiropractic Research Journal 1989; 1 (3): 23–36 ~ FULL TEXT The concept of subluxation has been a cornerstone of the theory and practice of chiropractic since its founding by D. D. Palmer [1] in 1895. It is one of the most controversial concepts in health care today, and finds its supporters and critics both within and outside the chiropractic profession. The original concept of the subluxation was that of a slightly misaligned vertebra, not sufficient to be qualified as a true luxation or dislocation but substantial enough to impinge on the segmental nerves associated with it. [1] While this original concept requires some modification in light of current research findings, there has been a wealth of knowledge accumulated in the past two decades that supports the concept of vertebral subluxations as a real entity. [2–9] It must be stressed that from the contemporary, scientific chiropractic point of view, the subluxation is a dynamic process, involving several tissue levels and integrative components.
	Review of the Literature Supporting a Scientific Basis for the Chiropractic Subluxation Complex J Manipulative Physiol Ther 1985 (Sep); 8 (3) Sep: 163–174 ~ FULL TEXT A review of the literature reveals strong evidence for both the mechanical model of disease production (structural) and the neurobiological model (functional). Outdated models which attempt to describe a scientific basis for chiropractic theory are inadequate and indeed harmful to the progress and acceptance of chiropractic.

Methods for Locating Fixated/Subluxated Segments

	Spinal Palpation A Chiro.Org article collection Review newer studues that demonstrate the reliability of palpation findings.
	Interexaminer Reliability of Seated Motion Palpation for the Stiffest Spinal Site J Manipulative Physiol Ther. 2018 (Sep); 41 (7): 571–579 ~ FULL TEXT More than half the time (54.3%) the examiners in this study agreed on the exact segment or at least the motion segment that was stiff in a given spinal region. The MedianAED for the combined dataset was 01.1 VE. This information supports high levels of interexaminer reliability for the SSS in each region of the spine and in the combined dataset. Reliability estimates based on absolute examiner differences were relatively higher and seemed to be more trustworthy than prior estimates based on discrete analysis and analysis with κ because the assessment method more closely resembled that used by clinicians in clinical practice. The reliability seen in this study is broadly consistent with previous studies of MP using continuous analysis.
	The Reliability of Spinal Motion Palpation Determination of the Location of the Stiffest Spinal Site is Influenced by Confidence Eatings: A Secondary Analysis of Three Studies Chiropractic & Manual Therapies 2016 (Dec 20); 24: 50 ~ FULL TEXT Neither the confidence module nor the subtyping by spinal region should obscure this study’s central finding: Motion Palpation (MP) for the “stiffest spinal site” (SSS) in the combined dataset, when analyzed using continuous data and related statistical methods, is reliable and appears to identify a clinically relevant and tightly constrained location for the stiffest spinal site; and the variability of the measured interexaminer differences is low. Using a stringent criterion of agreeing on at least the motion segment including the SSS, the described continuous measures palpation protocol was reliable 60.2–77.0% of the time for the combined dataset, and was 90.2% reliable when both examiners were confident. These findings support the view of some authors who have expanded the field of examiner agreement using motion palpation to include nominated segments that are within one level of each other. [30, 41]
	The Reliability of Lumbar Motion Palpation Using Continuous Analysis and Confidence Ratings: Choosing a Relevant Index of Agreement J Can Chiropr Assoc. 2016 (Jun); 60 (2): 146–157 ~ FULL TEXT Our results raise the possibility that the present inventory of reliability studies performed in the manual therapy professions, by having used mostly discrete study designs (certainly for MP) may have underestimated clinically relevant examiner agreement, thereby unduly discouraging further research and clinician interest in such research. Moreover, depending solely on ICC calculations to assess interexaminer agreement may result in flawed conclusions, when the subject population is relatively homogeneous. Greater reliance on variance-insensitive statistical functions would mitigate against that possibility. Future studies designed to analyze subsets of the data should use enough subjects to result in credible conclusions.
	Interexaminer Reliability of a Multidimensional Battery of Tests Used to Assess for Vertebral Subluxations Chiropractic Journal of Australia 2016; 46 (1): 100–117 ~ FULL TEXT In this study, high levels of interexaminer reliability were observed in each region of the spine when a multidimensional approach to detect vertebral subluxations was used. Since the combined MedAED for vertebral subluxations was 0.6VE, it can be stated with confidence that examiners usually agreed on at least the motion segment containing the most positive vertebral subluxation test indicators, and very frequently on the same segment. Vertebral subluxation assessment, when analyzed using continuous data, indicate much higher levels of agreement than has been heretofore associated with assessing agreement using discrete data and the Kappa statistic.
	Diagnostic and Treatment Methods Used by Chiropractors: A Random Sample Survey of Canada's English-speaking Provinces J Can Chiropr Assoc. 2015 (Sep); 59 (3): 279–287 ~ FULL TEXT Differential diagnosis is a standard part of the assessment of new chiropractic patients in English-speaking Canadian provinces and this is most commonly done using orthopaedic tests, palpation, history-taking, range of motion testing and neurological examination. The clinical tests/procedures used most commonly by these DCs to determine where to apply joint manipulation are palpation and painful joint findings. These methods are consistent with the current scientific literature. Chiropractic patients in Canada’s English-speaking provinces are treated with a combination of manual joint manipulation/mobilization, exercise, posture/ergonomic advice and soft-tissue therapies. These treatment methods are consistent with earlier analyses of Canadian DCs, but the data do suggest that chiropractors in Canada are increasingly using soft-tissue therapies as part of their therapeutic regimen.
	Validity of Palpation of the C1 Transverse Process: Comparison with a Radiographic Reference Standard J Can Chiropr Assoc 2015 (Jun); 59 (2): 91–100 ~ FULL TEXT Manual palpation of the C1 TVP can be very accurate and likely to direct a manual therapist or other health professional to the intended diagnostic or therapeutic target. This work is relevant to manual therapists, anesthetists, surgeons, and other health professionals.
	Review Of Methods Used By Chiropractors To Determine The Site For Applying Manipulation Chiropractic & Manual Therapies 2013 (Oct 21); 21 (1): 36 ~ FULL TEXT A considerable range of methods is in use for determining where in the spine to administer spinal manipulation. The currently published evidence falls across a spectrum ranging from strongly favourable to strongly unfavourable in regard to using these methods. In general, the stronger and more favourable evidence is for those procedures which take a direct measure of the presumptive site of care-methods involving pain provocation upon palpation or localized tissue examination. Procedures which involve some indirect assessment for identifying the manipulable lesion of the spine-such as skin conductance or thermography-tend not to be supported by the available evidence.
	Frequency of Use of Diagnostic and Manual Therapeutic Procedures of the Spine Taught at the Canadian Memorial Chiropractic College: A Preliminary Survey of Ontario Chiropractors. Part 1 - Practice Characteristics and Demographic Profiles J Can Chiropr Assoc. 2013 (Jun); 57 (2): 32–41 ~ FULL TEXT In general, the demographic profile of respondents to this survey was similar to respondents to previously published surveys. Respondents in this study were mostly male and graduates of CMCC. Most reportedly used Diversified technique and, notwithstanding the fact that is the principle technique taught to them, many field doctors continue to also use proprietary soft tissue techniques and often other chiropractic technique systems and therapeutic procedures not formally taught to them. Unlike previous studies, a relatively high number of respondents in this study reportedly used Upper Cervical techniques.
	Frequency of Use of Diagnostic and Manual Therapeutic Procedures of the Spine Currently Taught at the Canadian Memorial Chiropractic College: A Preliminary Survey of Ontario Chiropractors. Part 2 - Procedure Usage Rates J Can Chiropr Assoc. 2013 (Jun); 57 (2): 165–175 ~ FULL TEXT This study reported on the frequency of use of diagnostic and therapeutic procedures currently taught at CMCC by a group of pseudo-randomized Ontario chiropractors, most but not all of whom were CMCC graduates. The most commonly used diagnostic procedures for the cervical, thoracic, and lumbopelvic spine were joint play, static and motion palpation, neurological testing and ranges of motion. A number of other orthopaedic tests were less commonly used, and a number of tests were either rarely or not used at all, particularly in the assessment of the thoracic spine. With respect to therapeutic procedures of the spine, many mobilization and manipulative procedures are commonly used, with the exception of the ‘muscle’ manipulations of the cervical spine.
	Interexaminer Reliability of Cervical Motion Palpation Using Continuous Measures and Rater Confidence Levels J Can Chiropr Assoc. 2013 (Jun); 57 (2): 156–164 ~ FULL TEXT For the entire participant pool, ICC [2,1] = 0.61, judged "good." MAD=1.35 cm, corresponding to mean interexaminer differences of about 75% of one cervical vertebral level. Stratification by examiner confidence levels resulted in small subgroups with equivocal results. A continuous measures study methodology for assessing cervical motion palpation reliability showed more examiner concordance than was usually the case in previous studies using discrete methodology.
	Interexaminer Reliability of Thoracic Motion Palpation Using Confidence Ratings and Continuous Analysis J Chiropractic Medicine 2010 (Sep); 9 (3): 99–106 ~ FULL TEXT The confidence level of examiners has an effect on the interexaminer reliability of thoracic spine MP, such that agreement is “good” when examiners are “very confident” in their calls and not above chance levels when at least one of them is not. Looking at the data set as a whole, unstratified by degree of examiner confidence, our results resemble those of other investigators, in that the index of agreement is low. Thus, we believe using continuous measures methodology, and defining subgroups according to the confidence of the palpators, is more capable than level-by-level discrete analysis of detecting interexaminer agreement. We also believe our analytic method better reflects what motion palpators, who presumably look for maximally fixated levels within a spinal region logically related to a patient complaint, actually do.
	Motion Palpation Used as a Postmanipulation Assessment Tool for Monitoring End-Feel Improvement: A Randomized Controlled Trial of Test Responsiveness J Manipulative Physiol Ther. 2009 (Sep); 32 (7): 549–555 ~ FULL TEXT The findings of this study showed that motion palpation of end-feel assessment appears to be a responsive postmanipulation assessment tool in the cervical spine for determining whether perceived motion restriction found before treatment improves after SMT. This observation may be limited to symptomatic participants.
	Spinal Motion Palpation: A Comparison of Studies That Assessed Intersegmental End Feel vs Excursion J Manipulative Physiol Ther. 2008 (Oct); 31 (8): 616–626 ~ FULL TEXT The search strategy generated 415 citations, and 29 were harvested from reference lists. After removing articles that did not meet the inclusion criteria, 44 were considered relevant and appraised for quality. Fifteen studies focused on MP excursion, 24 focused on end feel, and 5 used both. Eight studies reported high levels of reproducibility (kappa = > or = 0.4), although 4 were not of acceptable quality, and 2 were only marginally acceptable. When only high-quality studies were considered, 3 of 24 end-feel studies reported good reliability compared with 1 of 15 excursion studies. There was no statistical support for a difference between the 2 groupings.
	Manual Examination of the Spine: A Systematic Critical Literature Review of Reproducibility J Manipulative Physiol Ther 2006 (Jul); 29 (6): 475–485 ~ FULL TEXT Palpation for pain is reproducible at a clinically acceptable level, both within the same observer and among observers. Palpation for global assessment (GA) is reproducible within the same observer but not among different observers. The level of evidence to support these conclusions is strong. The reproducibility of motion palpation (MP), soft tissue changes (STC) and static palpation (SP) is not clinically acceptable. The level of evidence is strong for interobserver reproducibility of MP and STC, whereas no evidence or conflicting evidence exists for SP and intraobserver reproducibility of STC. Results are overall robust with respect to the predefined levels of acceptable quality. However, the results are sensitive to changes in the preset level of clinically acceptable reproducibility and to the number of included studies.
	Diagnosis of Sacroiliac Joint Pain: Validity of Individual Provocation Tests and Composites of Tests Manual Therapy 2005 (Aug); 10 (3): 207–218 ~ FULL TEXT Provocation sacroiliac joint (SIJ) tests have significant diagnostic utility. Six provocation tests were selected on the basis of previously demonstrated acceptable inter-examiner reliability. Two of four positive tests (distraction, compression, thigh thrust or sacral thrust) or three or more of the full set of six tests are the best predictors of a positive intra-articular SIJ block. When all six SIJ provocation tests are negative, painful SIJ pathology may be ruled out.
	An Investigation into the Validity of Cervical Spine Motion Palpation Using Subjects with Congenital Block Vertebrae as a 'Gold Standard' BMC Musculoskelet Disord 2004 (Jun 15); 5 (1): 19 ~ FULL TEXT The results of this study indicate that even novice clinicians demonstrated the ability to correctly identify the presence or absence of known cervical spine intersegmental fixations by using specific motion palpation techniques on real patients with congenitally fused vertebrae. These congenital blocked vertebrae represent a true 'gold standard', allowing more accurate evaluation of the validity of motion palpation. The results of this study justify the clinical use of motion palpation in the diagnosis of true 'fixations' in the cervical spine.
	Joint Assessment – P.A.R.T.S. Topics in Clinical Chiropractic 2000; 7 (3): 1–10 ~ FULL TEXT Doctors of chiropractic are portals of entry to the health care system for many patients seeking health care services. As such, they must maintain broad and thorough assessment/diagnostic skills. Before employing any therapy, a clinician must first determine if there is a need for treatment. Therefore, the clinical information that any primary contact provider would want, including a case history, physical examination, clinical laboratory findings, radiographic findings, and any other tests necessary to check for suspected health problems, is needed. Having gathered and interpreted this information, it must be processed in order to arrive at a sound clinical conclusion. The role of this assessment process in the chiropractic office is to determine whether the patient should receive chiropractic care only, chiropractic care in concert with other forms of health care, or a referral to another health care professional for some other form of stand-alone management such as acute, crisis care. This article suggests the need for, and possible form of, a standardized assessment procedure for use by chiropractic clinicians.
	A Proposed Vertebral Subluxation Model Reflecting Traditional Concepts and Recent Advances in Health and Science J Vertebral Subluxation Research 1996 (Aug); 1 (1): 1–12 ~ FULL TEXT Part one of an expanded vertebral subluxation model (VSM) is presented which considers information from the traditional concept of vertebral subluxation, and other models including; the chiropractic subluxation complex, the vertebral subluxation complex, and the vertebral subluxation complex model. Other components, including health assessment and etiology, are to be introduced in the second part, and appropriate research designs for studying the expanded VSM are to be presented in the third part. All three parts discuss other models as well as classical and recent research findings which support the expanded VSM.
	Most Commonly Used Methods of Detecting Spinal Subluxation and the Preferred Term for its Description: A Survey of Chiropractors in Victoria, Australia J Manipulative Physiol Ther. 1997 (Nov); 20 (9): 583–589 The response rate was 85%. The most commonly used method was static palpation (mean score 6.6 +/- 1.1). Seven other methods, including pain description of the patient, orthopedic tests, motion palpation, visual posture analysis, leg length discrepancy, neurological tests and plain static X-rays had mean scores greater than 4.0. All of these methods, as well as functional X-ray views and kinesiological muscle testing, were considered reliable, with mean reliability scores greater than 4.0. Motion palpation was regarded as the most reliable method (mean reliability score 5.9 +/- 1.2). Seventy-five different terms for describing the spinal entity were named by 440 respondents. "Subluxation" was included in the preferred term of 294 respondents (67%), 46 included "dysfunction" (11%), 35 included "fixation" (8%) and 20 included "manipulable" (4.5%).
	The Accuracy of Manual Diagnosis for Cervical Zygapophysial Joint Pain Syndromes Med J Aust. 1988 (Mar 7); 148 (5): 233–236 The manipulative therapist identified correctly all 15 patients with proven symptomatic zygapophysial joints, and specified correctly the segmental level of the symptomatic joint. None of the five patients with asymptomatic joints was misdiagnosed as having symptomatic zygapophysial joints. Thus, manual diagnosis by a trained manipulative therapist can be as accurate as can radiologically-controlled diagnostic blocks in the diagnosis of cervical zygapophysial syndromes. However, before generalized claims about the reliability of manual diagnosis can be made, further studies of this nature are required to validate intertherapist reliability and the ability of manual techniques to diagnose other spinal pain syndromes.

Vertebral Subluxation Research Conferences

   The Research Agenda Conferences (RAC)
       A Chiro.Org article collection
         Catch up on all 26 of the RAC Conferences.
         Review the platform presentations, and enjoy the evolution of chiropractic research.

   The Upper Cervical Experience Conference ~ February 26th-28th, 2015
         Enjoy the 2015 abstracts!

   11th Annual Vertebral Subluxation Research Conference
         October 11-12, 2003 in Spartanburg, SC

   10th Annual Vertebral Subluxation Research Conference
         December 7-8, 2002 in Hayward, CA

   9th Annual Vertebral Subluxation Research Conference
         October 13-14, 2001 in Spartanburg, SC

   8th Annual Vertebral Subluxation Research Conference
         October 7-8, 2000 in Spartanburg, SC

   7th Annual Subluxation Conference
         October 9-10, 1999 in Spartanburg, SC

   6th Annual National Subluxation Conference
         October 10-11, 1998 in Atlantic City, NJ

	The Chiropractic Identity A Chiro.Org article collection Hold your horses! Before you read these fanciful Chiropractic Identity articles, which suggest that we all drop the dreaded subluxation-fixation hypothesis, so that we can assume the mantle as the Spinal Health Care Experts of the Universe, please read this thoughtful piece by a PhD-level sociologist (Caught in the Crosshairs), who also happens to be the wife of a chiropractor. Her insights into the political maneuvering in our profession are well worth the read
	Chiropractic, One Big Unhappy Family: Better Together or Apart? Chiropractic & Manual Therapies 2019 (Feb 21); 27: 4 It's with heavy heart that I realize that it's all come down to this: chiropractic depicted as a bad soap-opera marriage. What is more upsetting is that this article is penned by some of the best, brightest and most-published of our chiropractic researchers. I love these folks! That said, I'd like to challenge some of their assumptions. Chiropractic is not a marriage between chiropractors. At best, it's a Family. And families interact. I just might marry your sister, for example. Now you may not like me, or you may not like our marriage. But that's a personal problem. The word Evidence has taken on a sacred-cow glow lately, and is only eclipsed by the adoption of the word skeptic by every Tom, Dick and Harry blog-opinionist on the planet. So, let's set the stage for the conversation. This article dishes up several reasons why (as they call themselves) the 'evidence-friendly' faction are opposed to the 'traditional' group. Here's a short list of the infractions that are practiced by the 'traditionalists' They ‘believe’ in “subluxations” Some of them ‘believe’ that you can find “subluxations” on x-rays Some of them ‘believe’ that correcting “subluxations” leads to improved health So let's address these concerns, one at a time. Read more now.
	Chiropractic Conservatism and the Ability to Determine Contra-indications, Non-indications, and Indications to Chiropractic Care: A Cross-sectional Survey of Chiropractic Students Chiropractic & Manual Therapies 2019 (Feb 19); 27: 3 ~ FULL TEXT Chiropractic students are able to recognize contra-indications and indications but find it more challenging to identify non-indications in chiropractic clinical cases. Moreover, students who adhere to a conservative chiropractic approach systematically wish to treat patients, regardless of the symptoms, and even if they present with non-indications. The apparent presence of the conservative approach is of concern because it may predict a proportion of our future chiropractors scope of practice. Therefore, the determinants of this phenomenon need to be explored and understood.
	Chiropractic Identity: A Neurological, Professional, and Political Assessment J Chiropractic Humanities 2016 (Dec); 23 (1): 35–45 ~ FULL TEXT This article provides an overview of chiroractic identity from 6 points of view: (1)   concepts of manual medicine; (2)   areas of interest beyond the spine; (3)   concepts of the chiropractic subluxation; (4)   concepts of neurology; (5)   concepts of mainstream or alternative health care; and (6)   concepts of primary care, first-contact provider, or specialist.
	Analysis and Adjustment of Vertebral Subluxation as a Separate and Distinct Identity for the Chiropractic Profession: A Commentary J Chiropractic Humanities 2016 (Oct 25); 23 (1): 46–52 ~ FULL TEXT When a profession’s identity is not clear with respect to its area of interest and mission, then the public may be less inclined to seek its services. Identifying the chiropractic profession with a focus on vertebral subluxation would give the profession uniqueness not duplicated by other health care professions and therefore might legitimatize the existence of chiropractic as a health care profession. An identity having a focus on vertebral subluxation would also be consistent with the original intent of the founding of the chiropractic profession.
	Chiropractic Identity in the United States: Wisdom, Courage, and Strength J Chiropractic Humanities 2016 (Sep 15); 23 (1): 29–34 ~ FULL TEXT The various clinical specialties and independent groups in the chiropractic profession are so different in their beliefs, practice styles, and political agendas that a common identity is unlikely to be created. Areas of disagreement, including advanced practice, vertebral subluxation, and the philosophy of chiropractic, continue to separate those in the profession. Doctors of chiropractic should accept that differences within the profession will remain for the foreseeable future and that the profession should allow each group to live peacefully and supportively alongside each other. There's more on this topic at our Chiropractic Identity Page
	Subluxation and Semantics: A Corpus Linguistics Study J Can Chiropr Assoc. 2016 (Jun); 60 (2): 190–194 ~ FULL TEXT It was possible to identify 3 distinct concepts which were each referred to as 'subluxation:' i) an acute or instantaneous injurious event; ii) a clinical syndrome which manifested post-injury; iii) a physical lesion, i.e. an anatomical or physiological derangement which in most instances acted as a pain generator.   In fact, coherent implicit definitions of subluxation exist and may enjoy broad but subconscious acceptance. However, confusion likely arises from failure to distinguish which concept an author or speaker is referring to when they employ the term subluxation.
	Straight Chiropractic Philosophy As A Barrier To Medicare Compliance: A Discussion of 5 Incongruent Issues J Chiropractic Humanities 2013 (Oct 24); 20 (1): 19–26 ~ FULL TEXT The number of Medicare beneficiaries who used chiropractic spinal manipulation grew 13% from 2002 to 2004, remained flat through 2007, and then declined 5% through 2008. An estimated 1.7 million beneficiaries (6.9%) used 18.6 million allowed chiropractic services in 2008. In inflation-adjusted dollars, allowed charges per user increased 4% through 2005 and then declined by 17% through 2008; payments per user increased by 5% from 2002 to 2005 and then declined by 18% through 2008. Expenditures for chiropractic in 2008 totaled an estimated $420 million. Longitudinal trends in allowed claims for spinal manipulation varied by procedure: the relative frequency of treatment of one to two spinal regions declined from 43% to 29% of services, treatment of three to four regions increased from 48% to 62% of services, and treatment of five regions remained flat at 9% of services.
	A Diachronic Study of the Language of Chiropractic J Can Chiropr Assoc. 2013 (Mar); 57 (1): 49–55 ~ FULL TEXT This study investigates how the language of chiropractic has changed over time. A collection of material, published up until approximately 1950 and consisting of textbooks, monographs and lecture notes from Canadian Memorial Chiropractic College, was analyzed to identify commonly occurring words and phrases. The results were compared to a corpus of recent articles from the Journal of the Canadian Chiropractic Association. This permitted the identification of words which were over-represented in the historical literature and therefore likely have become somewhat archaic or represent themes which are of less import in the modern chiropractic literature. Words which were over-represented in the historical literature often referred to anatomical, pathological and biomechanical concepts. Conversely, words which were comparatively over-represented in the modern chiropractic literature often referred to concepts of professionalism, the clinical interaction and evidence-based care. A detailed analysis is presented of trends in the use of the conceptually important terms subluxation and adjustment.
	The Five Eras of Chiropractic & the Future of Chiropractic As Seen Through the Eyes of a Participant Observer Chiropractic & Manual Therapies 2012 (Jan 19); 20 (1): 1 ~ FULL TEXT Chiropractic has endured a turbulent history, marked by tremendous advances in areas such as education and licensing while marred by interprofessional conflict and a poor public image. The prolonged interprofessional conflict was instrumental in shaping the culture of chiropractic. These obstacles have long-since been removed although there are lingering effects from them. This article examines the chiropractic profession's history by dividing it into five Eras and suggests that there are three options available for the future of the profession. One: maintaining the status quo. Two: uniting under an evidence based scientific approach as partners in the health care delivery system that has buried the "one-cause, one-cure" sacred cow. The steps required to achieve this outcome are outlined. Three: openly dividing the profession into evidence based practitioners and subluxation based practitioners. Adopting this option would allow each branch of the profession to move forward in the health care delivery system unhindered by the other.It is unclear which option the profession will choose and whether the profession is mature enough to follow option two remains to be seen. What is evident is that the time to act is now.
	The Prevalence of the Term Subluxation in North American English-Language Doctor of Chiropractic Programs Chiropractic & Manual Therapies 2011 (Jun 17); 19: 14 ~ FULL TEXT Palmer College in Florida devoted 22.72% of its curriculum to courses mentioning the subluxation followed by Life University (Marietta, GA) and Sherman College with 16.44% and 12.80% respectively. As per specific coursework or subjects, an average of 5.22 courses or subjects have descriptions mentioning the term subluxation. Three schools made no mention of the term subluxation in their academic catalogs; they were National University of Health Sciences, Canadian Memorial Chiropractic College, and Southern California University of Health Sciences.
	Chiropractic at the Crossroads or Are We Just Going Around in Circles? Chiropractic & Manual Therapies 2011 (May 21); 19: 11 ~ FULL TEXT This paper is the author's perception of the many changes which have impacted, both positively and negatively, on chiropractic and the chiropractic profession over the past 30 years. Some of those changes have advanced the professional status of chiropractic, improved undergraduate training and paved the way for a research culture. Unfortunately, other changes, or lack of changes, have adversely affected the profession's growth, credibility and the public utilisation of chiropractic services in Australia. It would also appear, that the crossroads confronting the profession in Australia are not unique, as there are many parallels with what has occurred or is occurring internationally.
	Reflecting on 115 Years: The Chiropractic Profession's Philosophical Path J Chiropractic Humanities 2010 (Dec); 17 (1): 1–5 ~ FULL TEXT The chiropractic profession struggled with survival and identity in its first decades. In addition to internal struggles between chiropractic leaders and colleges, much of our profession's formative years were stamped with reactions to persecution from external forces. The argument that chiropractic should be recognized as a distinct profession, and the rhetoric that this medicolegal strategy included, helped to develop chiropractic identity during this period of persecution in the early 20th century. This article questions if the chiropractic profession is mature and wise enough to be comfortable in being proud of its past but still capable of continued philosophical growth.
	Historical Overview and Update on Subluxation Theories J Chiropractic Humanities 2010 (Dec); 17 (1): 22–32 ~ FULL TEXT This article presents a personal view of the historical evolution of theories of subluxation in the chiropractic profession. Two major themes emerge from this review: those related to the mechanical behavior of the spine and those related to the neurologic implications of these mechanical issues. Chiropractic subluxation theory is one of the few health-related theories whereby these mechanical and neurologic theories have been unified into a comprehensive theory of disorder of spinal function. For this disorder, doctors of chiropractic have used the term subluxation. These theories, and their unification in the “subluxation concept,” have undergone evolution in the profession's history. The “subluxation concept” currently faces challenges, which are briefly reviewed in this article. The only way forward is to strengthen our efforts to investigate the “subluxation concept” with high-quality scientific studies including animal models and human clinical studies.
	Subluxation – Historical Perspectives Chiropractic Journal of Australia 2009 (Dec); 39 (4): 11–164 ~ FULL TEXT The notion that by changing the word subluxation to another term we will somehow change the clinical, political, and philosophical connotations of the concept central to chiropractic practice is simply not rational. Changing the term used for the articular lesion treated by chiropractors (subluxation) does not eradicate the clinical, political, and philosophical issues that surround the construct; it obviously evades the issues. [30]
	Subluxation – Historical Perspectives Part II Chiropractic Journal of Australia 2009 (Dec); 39 (4): 143–150 ~ FULL TEXT Subluxation is a term that has been used by the chiropractic profession since its early days. The term, meaning less than a luxation, has been used for millennia, similarly so has manipulation been the preferred intervention to overcome this problem. This paper reviews some of the early uses of subluxation and manipulation identifying highlights, to help the reader appreciate that subluxation and manipulation, both spinal and general, are as old as civilisation itself.
	How Can Chiropractic Become a Respected Mainstream Profession? The Example of Podiatry Chiropractic & Osteopathy 2008 (Aug 29); 16: 10 ~ FULL TEXT The chiropractic profession has great promise in terms of its potential contribution to society and the potential for its members to realize the benefits that come from being involved in a mainstream, respected and highly utilized professional group. However, there are several changes that must be made within the profession if it is going to fulfill this promise. Several lessons can be learned from the podiatric medical profession in this effort.
	Subluxation: Dogma or Science? Chiropractic & Osteopathy 2005 (Aug 10); 13: 17 ~ FULL TEXT Subluxation syndrome is a legitimate, potentially testable, theoretical construct for which there is little experimental evidence. Acceptable as hypothesis, the widespread assertion of the clinical meaningfulness of this notion brings ridicule from the scientific and health care communities and confusion within the chiropractic profession. We believe that an evidence-orientation among chiropractors requires that we distinguish between subluxation dogma vs. subluxation as the potential focus of clinical research. We lament efforts to generate unity within the profession through consensus statements concerning subluxation dogma, and believe that cultural authority will continue to elude us so long as we assert dogma as though it were validated clinical theory.
	Chiropractic As Spine Care: A Model For The Profession Chiropractic & Osteopathy 2005 (Jul 6); 13: 9 ~ FULL TEXT This paper presents the spine care model as a means of developing chiropractic cultural authority and relevancy. The model is based on principles that would help integrate chiropractic care into the mainstream delivery system while still retaining self-identity for the profession. There are more articles like this at our Chiropractors As the Spinal Health Care Experts Page
	Dysafferentation: A Novel Term to Describe the Neuropathophysiological Effects of Joint Complex Dysfunction. A Look at Likely Mechanisms of Symptom Generation J Manipulative Physiol Ther 1998 (May); 21 (4): 267–280 ~ FULL TEXT Since the founding of the chiropractic profession, very few efforts have been made to thoroughly explain the mechanism(s) by which joint complex dysfunction generates symptoms. Save for a few papers, only vague and physiologically inconsistent descriptions have been offered. The purpose of this article is to propose a precise and physiologically sound mechanism by which symptoms may be generated by joint complex dysfunction. This thought provoking FULL TEXT article was released exclusively to Chiro.Org by National College of Chiropractic and JMPT. You may also enjoy this response from another chiropractic researcher.

Helpful Subluxation References

	Subluxation–based Guidelines A Chiro.Org article collection Please review this collection of treatment guidelines from the International Chiropractors Association (ICA) and the Council on Chiropractic Practice (CCP).
	Conditions That Respond Well to Chiropractic Care A Chiro.Org article collection Please review this assortment of articles, including case studies and randomized trials supporting chiropractic care for a variety of conditions other than neck or back pain.
	Radiologic Manifestations of Spinal Subluxations Chapter 6 from:   “Basic Chiropractic Procedural Manual” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter describes the radiologic signs that may be expected when spinal subluxations are demonstrable by radiography. Through the years, there have been several concepts within the chiropractic profession about what actually constitutes a subluxation. Each has had its rationale (anatomical, neurologic, or kinematic), and each has had certain validity contributing to our understanding of this complex phenomenon.
	Immune Function and Chiropractic A Chiro.Org article collection Chiropractic adjusting (spinal manipulation) appears to have an impact on immune cell lines. Review this collection of articles to learn more.
	A Vertebral Subluxation Hypothesis Tree A Chiro.Org article collection This presentation was originally given at the 4th Research Agenda Conference on July 25, 1999, in Chicago, IL. Thanks to Dr. Ed Owens for access to this PowerPoint file!
	Maintenance Care and Wellness and Chiropractic A Chiro.Org article collection Chiropractors are perfectly alligned to promote health, both by education and the provision of care. Review this collection of articles that support the chiropractic wellness model.
	The Role of Subluxation in Chiropractic The Foundation for Chiropractic Education and Research By Anthony L. Rosner, Ph.D. NOTE: This article ALSO contains the 2014 update, titled: Rephrasing the Subluxation: Capturing Lightning in a Bottle Every profession, whether health-related or not, develops its own special set of technical terms; its own language, if you will. Those terms typically have a meaning and context either formally or informally agreed upon by most if not all of the members of that profession. How then do we view the chiropractic subluxation?
	General Causes and Potential Effects of the Subluxation Complex Chapter 6 from:   “Basic Principles of Chiropractic Neuroscience” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter reviews the concepts underlying chiropractic articular therapy, with emphasis placed on neurologic implications. General etiology, manifestations, terminology, pertinent anatomical features, and applications are described.
	Neuroconceptual Models of Chiropractic Chapter 5 from:   “Basic Principles of Chiropractic Neuroscience” By Richard C. Schafer, D.C., FICC and the ACAPress This chapter offers a review of the highlights of preceding chapters that concern subluxation syndromes and forms a foundation of thought for following chapters.
	Basic Principles and Practice of Chiropractic Chapter 1 from:   “Basic Chiropractic Procedural Manual” By Richard C. Schafer, D.C., FICC and the ACAPress This introductory chapter describes the general causes and effects of the subluxation complex. The role of subluxation as an etiologic or perpetuating factor in disease is determined by the extent of the neuropathologic and/or biomechanical processes involved and how they relate to the creation, maintenance, or progress of such disorders.
	Basic Musculoskeletal Considerations Chapter 6 from:   “Chiropractic Physical and Spinal Diagnosis” By Richard C. Schafer, D.C., FICC and the ACAPress The skeletal system provides the body framework, shape, articulations, supports, it protects the vital organs, and it furnishes a place for muscle attachment. It provides protection for the internal organs, provides movement when acted upon by muscles, manufactures blood cells, and stores mineral salts. The muscular system moves and propels the body. In order for the skeletal and muscular systems to function properly, the nervous system gives the body awareness of its environment, enables it to react to stimuli from the environment, and allows the body to work as a unit by coordinating its activities. Inspection, palpation, and mensuration are the three most common techniques used in examination of the musculoskeletal system. As with all systems, a knowledge of anatomy and the pathophysiology involved is essential to make the examination significant.

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