The Degeneration Component of the Subluxation Complex      

This section is compiled by Frank M. Painter, D.C.
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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.


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