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

  1. “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]).

    1. This statement from the original white paper does not adequately express the state of chiropractic science.

    2. 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.

  2. 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.

    1. 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.

    2. 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.

    3. Determine if SM produces long-lasting changes in spinal biomechanics, which would presumably produce long-lasting changes in sensory input.

    4. 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.

  3. 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.

  4. Identify objective changes in the vertebral column that lead one to think that SM is needed.

    1. Use new technologies to determine changes in intersegmental stiffness.

    2. Determine if hyperalgesia is associated with the manipulable lesion.

    3. Determine whether the manipulable lesion is inflamed and, conversely, if inflammation of spinal and paraspinal tissues can cause the manipulable lesion.

  5. 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 Neurologic Component of Subluxation   

Chiropractic and Spinal Pain
A Chiro.Org article collection

Enjoy this collection of articles that reviews chiropractic's impressive impact on pain.

Non-musculoskeletal Disorders and Chiropractic
A Chiro.Org article collection

Enjoy this collection of articles discussuing chiropractic results with non-musculoskeletal complaints.

Vertigo, Balance and Chiropractic
A Chiro.Org article collection

Review this collection of studies that details chiropractic's impact on dizziness, balance and vertigo.

Neuroconceptual Models of Chiropractic
Chapter 5 from:   Basic Principles of Chiropractic Neuroscience

By Richard C. Schafer, D.C., FICC and the ACAPress
The structural spinal fault, the associated nerve involvement, and the ensuing functional alterations comprise classic chiropractic subluxation concepts. In contrast, limited concepts of spinal biomechanical faults, modes of possible nerve involvement, and etiologic rationales of functional changes promote narrow viewpoints, disciplines, and therapeutic approaches, as well as foster empiricism and dogma. Awareness of the varied concepts of structural lesions, neuroinsults, and the causes of abnormal functional changes promotes wider perspective for intuitive practices, multifaceted observations, and fewer practices with reliance on empiricism that is dictated by dogmatic frameworks.

Vertebral Subluxation and Systems Biology: An
Integrative Review Exploring the Salutogenic
Influence of Chiropractic Care on the
Neuroendocrine-Immune System

Cureus 2024 (Mar 15); 16 (3): e56223

In this paper we synthesize an expansive body of literature examining the multifaceted influence of chiropractic care on processes within and modulators of the neuroendocrine-immune (NEI) system, for the purpose of generating an inductive hypothesis regarding the potential impacts of chiropractic care on integrated physiology. Taking a broad, interdisciplinary, and integrative view of two decades of research-documented outcomes of chiropractic care, inclusive of reports ranging from systematic and meta-analysis and randomized and observational trials to case and cohort studies, this review encapsulates a rigorous analysis of research and suggests the appropriateness of a more integrative perspective on the impact of chiropractic care on systemic physiology. A novel perspective on the salutogenic, health-promoting effects of chiropractic adjustment is presented, focused on the improvement of physical indicators of well-being and adaptability such as blood pressure, heart rate variability, and sleep, potential benefits that may be facilitated through multiple neurologically mediated pathways. Our findings support the biological plausibility of complex benefits from chiropractic intervention that is not limited to simple neuromusculoskeletal outcomes and open new avenues for future research, specifically the exploration and mapping of the precise neural pathways and networks influenced by chiropractic adjustment.

A Randomized Controlled Trial Comparing Different
Sites of High-velocity Low Amplitude Thrust on
Sensorimotor Integration Parameters

Scientific Reports 2024 (Jan 12); 14 (1): 1159

This randomized controlled trial was the first to investigate the immediate changes in response to an HVLA thrust site selection in the cervical spine using a neurophysiological EEG outcome measure and found evidence that HVLA thrust directed at a cervical site considered as dysfunctional significantly reduces N30 amplitude immediately after such intervention. In contrast, HVLA thrust directed at a cervical site considered as non-dysfunctional causes no significant change. The present findings suggest that clinicians' selection of where to apply cervical HVLA thrust is likely to be relevant with regards to affecting the subsequent sensorimotor response. Further research is needed to correlate these changes with clinical outcomes, repeat the study design in other spinal regions and patient populations, and examine both potential changes at short, medium and long terms, as well as the longitudinal response to multiple HVLA thrust sessions.

The Effect of Spinal Adjustment/Manipulation on Immunity and
the Immune System: A Rapid Review of Relevant Literature

World Federation of Chiropractic. March 19, 2020

The world is currently in the midst of a global health crisis due to the spread of Coronavirus Disease 2019 (COVID-19). The World Health Organization (WHO) has declared COVID-19 a pandemic, meaning that it is being spread uncontrolled across country borders. At the time of writing, COVID-19 is affecting some 143 countries worldwide and there have been over 200,000 reported cases. As testing for COVID-19 has been limited, it is estimated that the true prevalence of COVID-19 is far greater than the situation reports have stated. WHO has issued information and guidance with a view to reducing the spread of COVID-19 and controlling the pandemic. This information has included correcting misinformation about COVID-19. The World Federation of Chiropractic (WFC) has supported WHO in its advice and recommendations and on March 17, 2020 issued an advice note to the worldwide chiropractic profession. One of the key messages contained in the WFC advice note highlighted the lack of credible, scientific evidence supporting claims of effectiveness of spinal adjustment / manipulation in boosting immunity and strengthening the immune system. Immunity is defined as the ability of an organism to resist disease, either through the activities of specialized blood cells or antibodies produced by them in response to natural exposure or inoculation, or by the injection of antiserum, or the transfer of antibodies from a mother to her baby via the placenta or breast milk. This rapid review considers materials the WFC is aware have been cited in support of claims of effectiveness for spinal adjustment / manipulation in conferring or enhancing immunity.

An Anatomical Study of the Suboccipital Cavernous Sinus and
its Relationship with the Myodural Bridge Complex

Clinical Anatomy 2023 (Jul); 36 (5): 726–736 ~ FULL TEXT

The suboccipital cavernous sinus (SCS) and the myodural bridge complex (MDBC) are both located in the suboccipital region. The SCS is regarded as a route for venous intracranial outflow and is often encountered during surgery. The MDBC consists of the suboccipital muscles, nuchal ligament, and myodural bridge and could be a power source for cerebrospinal fluid circulation. Intracranial pressure depends on intracranial blood volume and the cerebrospinal fluid. Since the SCS and MDBC have similar anatomical locations and functions, the aim of the present study was to reveal the relationships between them and the detailed anatomical characteristics of the SCS. The study involved gross dissection, histological staining, P45 plastination, and three-dimensional visualization techniques. The SCS consists of many small venous sinuses enclosed within a thin fibrous membrane that is strengthened by a fibrous arch closing the vertebral artery groove. The venous vessels are more abundant in the lateral and medial portions of the SCS than the middle portion. The middle and medial portions of the SCS are covered by the MDBC. Type I collagen fibers arranged in parallel and originating from the MDBC terminate on the SCS either directly or indirectly via the fibrous arch. The morphological features of SCS revealed in this research could serve as an anatomical basis for upper neck surgical procedures. There are parallel arrangements of type I collagen fibers between the MDBC and the SCS. The MDBC could change the blood volume in the SCS by pulling its wall during the head movement.

Neuromechanical Responses to Spinal Manipulation and
Mobilization: A Crossover Randomized Clinical Trial
J Manipulative Physiol Ther 2022 (Jan); 45 (1): 1–8 ~ FULL TEXT

In a controlled environment, the delivery of a thoracic spinal manipulation in participants with chronic midback pain resulted in an immediate decrease in thoracic pressure-provoked pain intensity but not spinal stiffness. Spinal mobilization has no effect on these 2 outcomes and generates lower thoracic muscle response than a spinal manipulation.

The Contemporary Model of Vertebral Column Joint Dysfunction
and Impact of High-velocity, Low-amplitude Controlled
Vertebral Thrusts on Neuromuscular Function

European J Applied Physiology 2021 (Oct); 121 (10): 2675–2720 ~ [Epub Jun 23] ~ FULL TEXT

Spinal adjustments of CSMC problems impact motor control in a variety of ways. These include increasing muscle force and preventing fatigue. These changes in neuromuscular function most likely occur due to changes in supraspinal excitability. The current contemporary model of the a central segmental motor control (CSMC) problem, and our understanding of the mechanisms of spinal adjustments, provide a biologically plausible explanation for how the vertebral column's central neural motor control can dysfunction, can lead to a self-perpetuating central segmental motor control problem, and how HVLA spinal adjustments can improve neuromuscular function.

The Potential Mechanisms of High-Velocity, Low-Amplitude,
Controlled Vertebral Thrusts on Neuroimmune Function:
A Narrative Review

Medicina (Kaunas) 2021 (Jun); 57 (6): 536 ~ FULL TEXT

There is substantial evidence suggesting that the nervous system, the hormonal system and the immune system communicate with one another and are intimately linked in their functions. [70, 93–97] This communication is essential for the body’s ability to protect itself and involves a variety of immune mediators, including cytokines, neurotransmitters, hormones, and humoral factors. [67, 68, 70, 94, 116, 117, 164, 234] Furthermore, the prefrontal cortex is critically involved in regulating the autonomic nervous system, the HPA axis, and the immune system. [94, 144–154] Neuro-immune communication is affected by emotional or pain-related stress. [69, 144, 151, 195, 260–262] Stress activates the SNS and HPA axis to increase inflammation in the body. Stress also suppresses the prefrontal cortex, which in turn reduces its inhibitory control on the HPA axis and inhibits the anti-inflammatory PNS activity.

The Effects of 4 Weeks of Chiropractic Spinal Adjustments
on Motor Function in People with Stroke:
A Randomized Controlled Trial
Brain Sciences 2021 (May 21); 11 (6): 676 ~ FULL TEXT

Improvements in motor function were observed when chiropractic care was added to 4 weeks of physical therapy care in people with subacute or chronic stroke. These improvements were statistically significant and a post-hoc responder analysis suggested they were also likely to be clinically significant. Chiropractic spinal adjustments may therefore be beneficial for people with motor impairments associated with subacute or chronic stroke. Further research, involving larger group sizes and longer-term follow-up and intervention periods, is required to corroborate these findings and further investigate the impacts of chiropractic care on motor function in people with stroke.

Neurophysiological Mechanisms of Chiropractic
Spinal Manipulation for Spine Pain

European Journal of Pain 2021 (Mar 31); [EPUB] ~ FULL TEXT

This narrative review highlights the most relevant mechanisms of pain relief by spinal manipulation and provides a perspective for future research on spinal manipulation and spine pain, including the validation of placebo interventions that control for placebo effects and other non-specific effects that may be induced by spinal manipulation.

Physiological Responses Induced by Manual Therapy in
Animal Models: A Scoping Review

Frontiers in Neuroscience 2020 (May 8); 14: 430 ~ FULL TEXT

Physiological responses related to manual therapy (MT) treatment have been investigated over decades using various animal models. However, these studies have not been compiled and their collective findings appraised. The purpose of this scoping review was to assess current scientific knowledge on the physiological responses related to MT and/or simulated MT procedures in animal models so as to act as a resource to better inform future mechanistic and clinical research incorporating these therapeutic interventions.

Low Back Pain: The Potential Contribution of Supraspinal
Motor Control and Proprioception

Neuroscientist 2019 (Dec); 25 (6): 583–596 ~ FULL TEXT

Research in the past two decades has provided important evidence how motor control adaptions in LBP might contribute to pain chronification through effects on spinal tissue loading, associated itself with degeneration of intervertebral discs and other tissues. However, the underlying biological and psychosocial interactions are still poorly understood and seem to vary across individuals, reflected in the modest effect sizes of motor control exercises, spurring a call for personalized interventional therapies [van Dieën and others 2018a]. Yet, to unleash the full potential of personalized treatments, more basic research on motor adaptions in LBP is mandatory, especially when considering the evolving evidence of cortical circuits in driving motor control adaptions during the course of LBP. Complementary findings from behavioral and neuroimaging studies underscore the prominent role of aberrant sensory processing in LBP.

The Effect of Spinal Manipulation on Brain Neurometabolites
in Chronic Nonspecific Low Back Pain Patients:
A Randomized Clinical Trial

Systematic Reviews 2019 (Nov 8); 8 (1): 267 ~ FULL TEXT

The current study was the first to investigate the metabolites of the brain following lumbopelvic manipulation in patients with NCLBP. The limitations of the current study were its high cost, being time-consuming, and 1.5-T magnetic field strength MRI. It is suggested that 3-T MRI be employed in future studies to measure glutamine and glutamate levels separately. Furthermore, another limitation is that we did not record psychosocial information to evaluate its relationship to changes of metabolites and pain. It is further recommended that the effect of other treatments (thermal therapy, physical therapy, exercise therapy, acupuncture) with spinal manipulation be evaluated on CNS by the 1H-MRS technique in patients with nonspecific chronic low back pain (NCLBP).

Proposed Neurobiological Processes Associated with Models of
Vertebral Subluxation: Dysafferentation, Dyskinesia,
Dysponesis, Dysautonomia, Neuroplasticity and
Ephaptic Transmission

Archives in Neurology & Neuroscience 2018 (Apr 4); 3 (1): 1–3 ~ FULL TEXT

Correction or reduction of vertebral subluxation facilitates the restoration of proper tone throughout the nervous system. Alterations in the tone of the somatic system may be objectively evaluated using surface EMG. Altered autonomic tone may be evaluated using skin temperature measurements. Changes in ranges of motion may be measured to assess dyskinesia. Such objective assessments have the potential to make correction of vertebral subluxation an important strategy in salutogenic healthcare. Additional ewsearch in this area may lead to improved clinical strategies.

The Effects of a Single Session of Spinal Manipulation
on Strength and Cortical Drive in Athletes

Eur J Appl Physiol 2018 (Apr); 118 (4): 737-749 ~ FULL TEXT

A single session of SM of dysfunctional spinal and pelvic joints increased muscle strength and cortical drive to ankle plantar flexor muscles in elite Taekwondo athletes. The increased MVC force lasted for 30 min and the cortical drive increase persisted for at least 60 min. Further research is now required to determine whether the observed changes are important for athletic performance.

Subclinical Recurrent Neck Pain and its Treatment Impacts Motor
Training-induced Plasticity of the Cerebellum and Motor Cortex

PLoS One. 2018 (Feb 28); 13 (2): e0193413 ~ FULL TEXT

The presence of neck pain alters both neck and limb sensorimotor function and motor control [9], and even milder forms of neck dysfunction can impact sensorimotor function. [21, 22] These studies were performed with subclinical neck pain participants, or people with untreated mild-to-moderate recurrent neck pain. [23, 24] Such recurrent pain represents a promising model to investigate long term consequences of altered sensory input from the neck on SMI. Whether subclinical recurrent neck pain alters motor learning is currently unknown. If this is the case, it could help explain why maladaptive motor patterns are maintained, potentially setting up a cycle of recurrent and chronic pain. There is a large body of evidence that reveals structural and functional changes within the CNS of people with chronic musculoskeletal disorders. [25] These changes may initially be beneficial, but as they persist they are thought to be influential in the pathophysiology of the condition and the developmental recurrence and maintenance of chronic symptoms. [25] Neuroplastic changes within different areas of the CNS are likely to help explain the transition from acute to recurrent to chronic conditions, sensory-motor findings, perceptual disturbances, why some individuals continue to experience pain when no structural cause can be discerned and why some fail to respond to conservative interventions in subjects with chronic musculoskeletal disorders. [25]

Association of Subclinical Neck Pain With Altered
Multisensory Integration at Baseline and 4-Week
Follow-up Relative to Asymptomatic Controls

J Manipulative Physiol Ther. 2018 (Feb); 41 (2): 81–91 ~ FULL TEXT

This is the first study to report that people with subclinical neck pain (SCNP) have slower visual and multisensory response times than asymptomatic individuals. These differences persist over 4 weeks, suggesting that the multisensory technique is reliable and that these differences in the SCNP group do not improve on their own in the absence of treatment.

Sustained Improvement of Heart Rate Variability in
Patients Undergoing a Program of Chiropractic Care:
A Retrospective Case Series

Chiropractic Journal of Australia 2018; 45 (4):338–358 ~ FULL TEXT

Patients receiving continuous chiropractic care to correct vertebral subluxation demonstrated a sustained improvement in heart rate variability (HRV). This novel finding objectively demonstrates long-term change consistent with improved neurophysiological regulation, adaptability and resilience in patients undergoing chiropractic care, and suggests the utility of chiropractic care for outcomes greater than only musculoskeletal improvements.

Characteristics of Paraspinal Muscle Spindle
Response to Mechanically Assisted Spinal
Manipulation: A Preliminary Report

J Manipulative Physiol Ther 2017 (Jul); 40 (6): 371–380 ~ FULL TEXT

Short duration (<10 ms) MAM thrusts decrease muscle spindle discharge with a majority of afferents requiring prolonged periods (>6 seconds) to return to baseline MF activity. Physiological consequences and clinical relevance of described MAM mechanoreceptor responses will require additional investigation.

Unravelling Functional Neurology: A Scoping Review of
Theories and Clinical Applications in a Context of
Chiropractic Manual Therapy

Chiropractic & Manual Therapies 2017 (Jul 18); 25: 19 ~ FULL TEXT

Functional Neurology (FN) gives the impression to be a complex alternative to the old variant of the chiropractic subluxation model, in which the vertebral subluxation is replaced by "physiological lesions" of the brain, and the treatment, spinal adjustments, are complemented by various neurological stimuli. Both models purport to treat not the symptoms but the cause. We conclude there is a need for more scientific documentation on the validity of FN.

Effect of Radiofrequency Denervation on Pain Intensity
Among Patients With Chronic Low Back Pain:
The Mint Randomized Clinical Trials

JAMA. 2017 (Jul 4); 318 (1): 68–81 ~ FULL TEXT

In 3 randomized clinical trials of participants with chronic low back pain originating in the facet joints, sacroiliac joints, or a combination of facet joints, sacroiliac joints, or intervertebral disks, radiofrequency denervation combined with a standardized exercise program resulted in either no improvement or no clinically important improvement in chronic low back pain compared with a standardized exercise program alone. The findings do not support the use of radiofrequency denervation to treat chronic low back pain from these sources.

Effects of 12 Weeks of Chiropractic Care on Central
Integration of Dual Somatosensory Input in Chronic
Pain Patients: A Preliminary Study

J Manipulative Physiol Ther. 2017 (Mar); 40 (3): 127–138 ~ FULL TEXT

The dual SEP ratio technique appears to be sensitive enough to measure changes in cortical intrinsic inhibitory interactions in patients with chronic neck pain. The observations in 6 subjects revealed that 12 weeks of chiropractic care improved suppression of SEPs evoked by dual upper limb nerve stimulation at the level of the motor cortex, premotor areas, and/or subcortical areas such as basal ganglia and/or thalamus. It is possible that these findings explain one of the mechanisms by which chiropractic care improves function and reduces pain for chronic pain patients.

Glucose Metabolic Changes in the Brain and Muscles of Patients
with Nonspecific Neck Pain Treated by Spinal
Manipulation Therapy: A [18F]FDG PET Study

Evid Based Complement Alternat Med. 2017 (Jan 12); 2017: 4345703 ~ FULL TEXT

Changes in brain activity after SMT included activation of the dorsal anterior cingulate cortex, cerebellar vermis, and somatosensory association cortex and deactivation of the prefrontal cortex and temporal sites. Glucose uptake in skeletal muscles showed a trend toward decreased metabolism after SMT, although the difference was not significant. Other measurements indicated relaxation of cervical muscle tension, decrease in salivary amylase level (suppression of sympathetic nerve activity), and pain relief after SMT.

Cervical Spine Disorders and its Association with Tinnitus:
The "Triple" Hypothesis

Med Hypotheses. 2017 (Jan); 98: 2–4 ~ FULL TEXT

Conceivably, cervical spine disorders could trigger a somatosensory pathway-induced disinhibition of dorsal cochlear nucleus (DCN) activity in the auditory pathway; furthermore, CSD can cause inner ear blood impairment induced by vertebral arteries hemodynamic alterations and trigeminal irritation.

Impact of Spinal Manipulation on Cortical Drive to Upper
and Lower Limb Muscles

Brain Sci. 2017 (Jan); 7 (1): 2 ~ FULL TEXT

Spinal manipulation may therefore be indicated for the patients who have lost tonus of their muscle and/or are recovering from muscle degrading dysfunctions such as stroke or orthopaedic operations and/or may also be of interest to sports performers. These findings should be followed up in the relevant populations.

The Physiological Role of Tumor Necrosis Factor in
Human Immunity and Its Potential Implications
in Spinal Manipulative Therapy

J Chiropractic Medicine 2016 (Sep); 15 (3): 190–196 ~ FULL TEXT

Physiological roles of tumor necrosis factor (TNF) have recently regained attention in the biomedical research community; new findings, particularly with the discovery of the interaction between TNF and Tregs, offer new insights to understanding human immunophysiology. This progress may provide a new paradigm in understanding SMT.

Effectiveness of Chiropractic Care to Improve Sensorimotor
Function Associated With Falls Risk in Older People:
A Randomized Controlled Trial

J Manipulative Physiol Ther. 2016 (May); (39) 4: 267–278 ~ FULL TEXT

Over 12 weeks, the chiropractic group improved compared with the control group in choice stepping reaction time (119 milliseconds; 95% confidence interval [CI], 26–212 milliseconds; P = .01) and sound-induced flash illusion (13.5%; 95% CI, 2.9%–24.0%; P = .01). Ankle joint position sense improved across the 4- and 12-week assessments (0.20°; 95% CI, 0.01°–0.39°; P = .049). Improvements were also seen between weeks 4 and 12 in the SF–36 physical component of quality of life (2.4; 95% CI, 0.04–4.8; P = .04) compared with control.

Manipulation of Dysfunctional Spinal Joints Affects
Sensorimotor Integration in the Prefrontal Cortex:
A Brain Source Localization Study

Neural Plast. 2016 (Mar 7); 2016: 3704964 ~ FULL TEXT

This study resulted in two major findings. Firstly, this study reproduced previous findings of SEPs studies that have shown that adjusting dysfunctional spinal segments alters early sensorimotor integration (SMI) of input from the upper limb (as evidenced with a decrease in N30 SEP complex amplitudes). [3, 6, 21]

The second major finding of this study was that we were able to show, using dipole source localization, that this change in SMI that occurs after spinal manipulation predominantly happens in the prefrontal cortex.

The Impact of Chiropractic Spinal Adjusting
(Spinal Manipulation) On Pain Modulation

See also:  
Chiropractic and Spinal Pain

   On The Origin of Atraumatic Neuromusculoskeletal Pain
Chiropractic Journal of Australia 2016 (Jan); 44 (1): 1–8 ~ FULL TEXT

The purpose of this study was to examine the possible origins of non-specific or atraumatic back pain by applying the Gate Theory of pain and current physiologic concepts. I present a theory that accounts for the initiation and potential consequences of neuromusculoskeletal pain incorporating failure of the mechanism of muscle relaxation and resulting in pain and compromise of the lymphatic system. The theory provides an alternative to current theories and hypotheses of the cause and consequences of neuromusculoskeletal pain.

The Effect of Spinal Manipulation on Deep Experimental
Muscle Pain in Healthy Volunteers

Chiropractic & Manual Therapies 2015 (Sep 7); 23: 25 ~ FULL TEXT

The current findings do not support the theory that HVLA-manipulation has a non-specific, reflex-mediated local or generalized analgesic effect on experimentally induced deep muscle pain. This in turn suggests, that any clinical analgesic effect of HVLA-manipulation is likely related to the amelioration of a pre-existing painful problem, such as reduction of biomechanical dysfunction.

Changes in Pain Sensitivity Following Spinal Manipulation:
A Systematic Review and Meta-analysis

J Electromyogr Kinesiol. 2012 (Oct); 22 (5): 752–767 ~ FULL TEXT

Spinal manipulation (SMT) demonstrated a favorable effect over other interventions on increasing PPT. Subgroup analysis showed a significant effect of SMT on increasing mechanical pressure pain threshold (PPT) at the remote sites of stimulus application supporting a potential central nervous system mechanism. Future studies of SMT related hypoalgesia should include multiple experimental stimuli and test at multiple anatomical sites.

The Effect of Spinal Manipulative Therapy on Experimentally
Induced Pain: A Systematic Literature Review

Chiropractic & Manual Therapies 2012 (Aug 10); 20 (1): 26 ~ FULL TEXT

Twenty-two articles were included, describing 43 experiments, primarily on pain produced by pressure (n = 27) or temperature (n = 9). Their quality was generally moderate. A hypoalgesic effect was shown in 19/27 experiments on pressure pain, produced by pressure in 3/9 on pain produced by temperature and in 6/7 tests on pain induced by other measures. Second pain provoked by temperature seems to respond to SMT but not first pain. Most studies revealed a local or regional hypoalgesic effect whereas a systematic effect was unclear. Manipulation of a "restricted motion segment" ("manipulable lesion") seemed not to be essential to analgesia. In relation to outcome, there was no discernible difference between studies with higher vs. lower quality scores.

What is Different About Spinal Pain?
Chiropractic & Manual Therapies 2012 (Jul 5); 20 (1): 22 ~ FULL TEXT

This thesis addressed the question "what is different about spine pain?"   Neuroanatomic and neurophysiologic findings from studies in the last twenty years provide preliminary support for the thesis that deep spine pain is different from deep pain arising from peripheral limb structures.

Spinal Manipulative Therapy and Its Role in the
Prevention, Treatment and Management f Chronic Pain

J Canadian Chiro Assoc 2012 (Mar); 56 (1): 5–7 ~ FULL TEXT

Chronic pain is a worldwide epidemic. It is characterized as “pain that persists beyond normal tissue healing time” [1] and is physiologically distinct from acute nociceptive pain. The current research estimates the prevalence of chronic pain in the general population to be anywhere from 10–55%, [2] predominantly affecting the adult population. Studies indicate that the prevalence of chronic pain in the over–60 age group is double that for younger adults. [3] Furthermore, over 80% of elderly (over 65) adults suffer from some form of painful chronic joint disease [4] and greater than 85% of the general population will experience some form of chronic myofascial pain during their lifetime. [5]

Does Facet Joint Inflammation Induce Radiculopathy?
An Investigation Using a Rat Model of Lumbar
Facet Joint Inflammation

Spine (Phila Pa 1976) 2007 (Feb 15); 32 (4): 406–412

The association between lumbar facet joint inflammation and radiculopathy was investigated using behavioral, histologic, and immunohistochemical testing in rats. Both mechanical and chemical factors have been identified as important for inducing radiculopathy. In lumbar spondylosis, facet joint osteophytes may contribute to nerve root compression, which may induce radiculopathy. Furthermore, inflammation may occur in the facet joint, as in other synovial joints. Inflamed synovium may thus release inflammatory cytokines and induce nerve root injury with subsequent radiculopathy. (In this study) when inflammation was induced in a facet joint, inflammatory reactions spread to nerve roots, and leg symptoms were induced by chemical factors. This work supports yet another aspect of the Vertebral Subluxation Complex hypothesis.

Spinal Manipulation Reduces Pain and Hyperalgesia After
Lumbar Intervertebral Foramen Inflammation in the Rat

J Manipulative Physiol Ther. 2006 (Jan); 29 (1): 5–13 ~ FULL TEXT

These studies show that Activator-assisted spinal manipulative therapy (ASMT) can significantly reduce the severity and shorten the duration of pain and hyperalgesia caused by lumbar IVF inflammation. This effect may result from ASMT-induced faster elimination of the inflammation and recovery of excitability of the inflamed DRG neurons by improving blood and nutrition supplement to the DRG within the affected IVF. Manipulation of a specific spinal segment may play an important role in optimizing recovery from lesions involving IVF inflammation.

Chronic Pain in Persons With Neuromuscular Disease
Clin J Pain 2005 (Jan); 21 (1): 18–26 ~ FULL TEXT

In this paper, researchers in a medical school rehabilitation department were interested in finding out what treatments were most effective at reducing pain for neuromuscular diseases (like amyotrophic lateral sclerosis and myotonic muscular dystrophies).
Chiropractic scored the highest pain relief rating (7.33 out of 10), scoring higher than the
relief provided by either nerve blocks (
6.75) or opioid analgesics (6.37). WOW!!!

Joint Manipulation Reduces Hyperalgesia By Activation of
Monoamine Receptors But Not Opioid or GABA Receptors
in the Spinal Cord

Pain. 2003 (Nov); 106 (1–2): 159–168 ~ FULL TEXT

Joint manipulation has long been used for pain relief. However, the underlying mechanisms for manipulation-related pain relief remain largely unexplored. The purpose of the current study was to determine which spinal neurotransmitter receptors mediate manipulation-induced antihyperalgesia. Rats were injected with capsaicin (50 microl, 0.2%) into one ankle joint and mechanical withdrawal threshold measured before and after injection. The mechanical withdrawal threshold decreases 2 h after capsaicin injection.

Qualitative Review of Studies of Manipulation-induced Hypoalgesia
J Manipulative Physiol Ther 2000 (Feb); 23 (2): 134–138

From the early 1990s, there are several reports involving the use of the pressure algometer initially devised by Fischer. [24] Vernon [25] was the first to report the improvement in paraspinal pressure pain threshold (PPT) levels after manipulation. Six tender muscle spots were measured bilaterally in a subject with chronic right-sided neck and scapular pain. The right side muscle values were all significantly lower than those on the left and were lower than the normal cut-off value of 3.5 kg/cm2 established by Fischer. [24] After a cervicoscapular manipulation, PPT levels rose by an average of 45%, whereas the patient's pain score dropped from 6 to 1/10 on a 10-centimeter VAS. In 1992, Vernon et al [12] reported on 9 subjects with chronic neck pain. Baseline PPT values were obtained bilaterally around the painful segment (fixation) for a total of 4 measured sites. Five subjects were randomly assigned to receive a rotary manipulation, and 4 subjects received the same sort of oscillatory mobilization that had been used in the endorphin study. [21] In the group receiving manipulation, PPT levels at 5 minutes after treatment rose at all 4 sites (ie, bilaterally) an average of 45%, whereas in the control group there was no increase. This difference was statistically significant at all 4 points.

Joint Position Sense Error in People With Neck Pain:
A Systematic Review

Man Ther. 2015 (Dec); 20 (6): 736–744

Several studies in recent decades have examined the relationship between proprioceptive deficits and neck pain. However, there is no uniform conclusion on the relationship between the two. Clinically, proprioception is evaluated using the Joint Position Sense Error (JPSE), which reflects a person's ability to accurately return his head to a predefined target after a cervical movement.

Neural Responses to the Mechanical Characteristics of High
Velocity, Low Amplitude Spinal Manipulation:
Effect of Specific Contact Site

Man Ther. 2015 (Dec); 20 (6): 797–804 ~ FULL TEXT

This animal study showed that contact site for an HVLA-SM can have a significant effect on the magnitude of sensory input arising from muscle spindles in the back.

Paraspinal Muscle Spindle Response to Intervertebral Fixation
and Segmental Thrust Level During Spinal Manipulation
in an Animal Model

Spine (Phila Pa 1976) 2015 (Jul 1); 40 (13): E752–759 ~ FULL TEXT

Intervertebral fixation decreases muscle spindle discharge during target HVLA-SM in a cat model. While HVLA-SM target accuracy maximizes spindle response, non-target thrust muscle spindle response is substantial and possibly provides a neurophysiological rationale for clinical efficacy despite low levels of inter-examiner reliability in determining optimal specific sites for HVLA-SM.

Changes in H-reflex and V-waves Following Spinal Manipulation
Exp Brain Res. 2015 (Apr); 233 (4): 1165–1173 ~ FULL TEXT

This study is the first to indicate that the chiropractic adjustments of the spine can actually induce significant changes in the net excitability for the low-threshold motor units, and/or alters the synaptic efficacy of the Ia synapse with these low-threshold homonymous motoneurons. The study also indicates that spinal manipulation can improve the confidence of the subject to activate his/her muscle as evidence with the increase in the SEMG signals and force during MVC, and/or alters motor neuron recruitment patters. The results suggest that the improvements in MVC following spinal manipulation are likely attributed to the increased descending drive and/or modulation in afferents. They also indicate that spinal manipulation prevents fatigue. Spinal manipulation may therefore be indicated as part of the medical treatment for the patients who have lost tonus of their muscle and or are recovering from muscle degrading dysfunctions such as stroke or orthopedic operations. These results may also be of interest to sports performers. We suggest these findings should be followed up in the relevant populations.

Spinal Manipulative Therapy-specific Changes in Pain
Sensitivity in Individuals with Low Back Pain

Journal of Pain 2014 (Feb); 15 (2): 136–148 ~ FULL TEXT

Participants receiving the SMT and placebo SMT received their assigned intervention 6 times over 2 weeks. Pain sensitivity was assessed prior to and immediately following the assigned intervention during the first session. Clinical outcomes were assessed at baseline and following 2 weeks of participation in the study. Immediate attenuation of suprathreshold heat response was greatest following SMT (P = .05, partial η2 = .07). Group-dependent differences were not observed for changes in pain intensity and disability at 2 weeks. Participant satisfaction was greatest following the enhanced placebo SMT.

Alterations in Cortical and Cerebellar Motor Processing
in Subclinical Neck Pain Patients Following
Spinal Manipulation

J Manipulative Physiol Ther. 2013 (Oct); 36 (8): 527–537 ~ FULL TEXT

The subclinical neck pain (SCNP) group showed a significant improvement in task performance as indicated by a 19% decrease in mean reaction time (P < .0001), which occurred concurrently with a decrease in cerebellar inhibition (CBI) following the combined spinal manipulation and motor sequence learning intervention (F1,6 = 7.92, P < .05). The control group also showed an improvement in task performance as indicated by a 25% increase in reaction time (P < .001) with no changes to CBI.

Effects of Cervical Joint Manipulation on Joint Position
Sense of Normal Adults

J Phys Ther Sci 2013 (Jun); 25 (6): 721–723~ FULL TEXT

Cervical joint manipulation reduced JPE and improved joint position sence. Therefore, we consider its application to the treatment of patients with cervical problems in clinical practice is desirable.

Visceral Responses to Spinal Manipulation
J Electromyogr Kinesiol. 2012 (Oct); 22 (5): 777–784 ~ FULL TEXT

While spinal manipulation is widely seen as a reasonable treatment option for biomechanical disorders of the spine, such as neck pain and low back pain, the use of spinal manipulation to treat non-musculoskeletal complaints remains controversial. This controversy is due in part to the perception that there is no robust neurobiological rationale to justify using a biomechanical treatment of the spine to address a disorder of visceral function. This paper therefore looks at the physiological evidence that spinal manipulation can impact visceral function. A structured search was conducted, using PubMed and the Index to Chiropractic Literature, to construct of corpus of primary data studies in healthy human subjects of the effects of spinal manipulation on visceral function.

The Decreased Responsiveness of Lumbar Muscle Spindles to
a Prior History of Spinal Muscle Lengthening is Graded
with the Magnitude of Change in Vertebral Position

J Electromyogr Kinesiol. 2012 (Dec); 22 (6): 814–820 ~ FULL TEXT

Stability, robustness and performance are attributes of the lumbar spine as a mechanical system that depend upon of a variety of biological mechanisms [McGill et al, 2003, Reeves et al, 2007, Solomonow 2011]. Which mechanisms become engaged depends upon both the biomechanical behavior of the spine’s passive components (connective tissue comprising the intervertebral disc, tendons, ligaments, fascia, and non-contractile elements within paraspinal muscles) and the physiological behavior of the spine’s active components (paraspinal muscle’s contractile capacity and neural elements that control the recruitment, timing and magnitude of this contractile capacity) [McGill et al, 2003, Panjabi 1992, Reeves et al, 2007, Solomonow 2011]. A locus of direct interface between these two components is at receptive nerve endings in peripheral tissues. Somatosensory feedback signals are initiated here when these endings respond to their local biomechanical, thermal, or chemical environments. It has been suggested that feedback signals can become corrupted when biomechanical conditions adversely affect the mechanical behavior of the spine’s passive components [Reeves et al, 2007, Solomonow 2011]. For example, creep in the lumbar tissues from prolonged cyclic and static loading alters the normal activity of multifidus muscle and potentially compromises spinal stability [Solomonow et al, 2003].

The Role of Spinal Manipulation in Addressing Disordered
Sensorimotor Integration and Altered Motor Control

J Electromyogr Kinesiol. 2012 (Oct); 22 (5): 768–776 ~ FULL TEXT

This review provides an overview of some of the growing body of research on the effects of spinal manipulation on sensory processing, motor output, functional performance and sensorimotor integration. It describes a body of work using somatosensory evoked potentials (SEPs), transcranial magnetic nerve stimulation, and electromyographic techniques to demonstrate neurophysiological changes following spinal manipulation. This work contributes to the understanding of how an initial episode(s) of back or neck pain may lead to ongoing changes in input from the spine which over time lead to altered sensorimotor integration of input from the spine and limbs.

Spinal Manipulative Therapy and Somatosensory Activation
J Electromyogr Kinesiol. 2012 (Oct); 22 (5): 785–794 ~ FULL TEXT

The goal of this article is to briefly update our knowledge regarding several physical characteristics of an applied SMT, and review what is known about the signaling characteristics of sensory neurons innervating the vertebral column in response to spinal manipulation. Based upon the experimental literature, we propose that SMT may produce a sustained change in the synaptic efficacy of central neurons by evoking a high frequency, bursting discharge from several types of dynamically-sensitive, mechanosensitive paraspinal primary afferent neurons.

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.

Cortical Changes in Chronic Low Back Pain: Current State
of the Art and Implications for Clinical Practice

Man Ther. 2011 (Feb); 16 (1): 15–20 ~ FULL TEXT

There is increasing evidence that chronic pain problems are characterised by alterations in brain structure and function. Chronic back pain is no exception. There is a growing sentiment, with accompanying theory, that these brain changes contribute to chronic back pain, although empirical support is lacking. This paper reviews the structural and functional changes of the brain that have been observed in people with chronic back pain. We cast light on the clinical implications of these changes and the possibilities for new treatments but we also advise caution against concluding their efficacy in the absence of solid evidence to this effect.

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.

Spinal Motor Neuronal Degeneration After Knee Joint
Immobilization in the Guinea Pig

J Manipulative Physiol Ther. 2010 (Jun); 33 (5): 328–337 ~ FULL TEXT

After various periods of knee joint immobilization, a variety of features of motor neuronal degeneration were observed. Specific characteristics included gradual increases in the expressions of neuronal nitric oxide synthase and ultrastructural changes in affected motor neurons including reduction of cell organelles, indentation of the nuclear envelop, and small compact clumps of chromatin in the nuclei. We conclude that motor neuronal degeneration in the spinal cord and axons in this study was the result of knee joint immobilization. Increases in motor neuronal nitric oxide-mediated oxidative stress level after reduction of target tissue activity may contribute to the mechanism for degenerative changes in the motor neurons in adult spinal cord of the guinea pig.

The Effects of Spinal Manipulation on Central Integration
of Dual Somatosensory Input Observed After Motor Training:
A Crossover Study

J Manipulative Physiol Ther. 2010 (May); 33 (4): 261–272 ~ FULL TEXT

These findings may help to clarify the mechanisms responsible for the effective relief of pain and restoration of functional ability documented after spinal manipulation and the mechanism involved in the initiation of overuse injuries.

Altered Central Integration of Dual Somatosensory Input
After Cervical Spine Manipulation

J Manipulative Physiol Ther. 2010 (Mar); 33 (3): 178–188 ~ FULL TEXT

This study suggests that cervical spine manipulation may alter cortical integration of dual somatosensory input. These findings may help to elucidate the mechanisms responsible for the effective relief of pain and restoration of functional ability documented after spinal manipulation treatment.

Exploring the Neuromodulatory Effects of the Vertebral
Subluxation and Chiropractic Care

Chiropractic Journal of Australia 2010 (Mar); 40 (1): 37–44 ~ FULL TEXT

Over the past 15 years our research group has been conducting a variety of experiments aimed at testing out the theory that adjusting subluxations improves central nervous system functioning and overall expression of health and well being. To do this the theory was first formulated into a model (Figure 2) that could be scientifically tested with a programme of research studies. This model became the basis for the lead author’s PhD research, [5] and continues to be a foundational premise that our research group is attempting to elucidate with our work. The model was constructed using early chiropractic research data and a thorough review of the neurophysiology scientific literature.

Positive Patient Outcome After Spinal Manipulation in a Case
of Cervical Angina

Man Ther. 2009 (Dec); 14 (6): 702–705 ~ FULL TEXT

This case identified an individual with the under diagnosed phenomena of cervical angina. This patient demonstrated a sustained improvement up to 11 weeks following a brief trial of SMT directed to the cervicothoracic region, suggesting a mechanically based, musculoskeletal etiology to her presentation. Future prospective studies are needed to assess the viability of a course of SMT management, and the consideration of related treatments such as grade I–IV joint mobilisation for patients who have tested negative for true angina, but continue to present with unrelenting atypical chest and upper extremity pain prior to directing them for surgical management.

Spinal Manipulative Therapy Has an Immediate Effect on
Thermal Pain Sensitivity in People With Low Back Pain:
A Randomized Controlled Trial

Phys Ther. 2009 (Dec); 89 (12): 1292–1303 ~ FULL TEXT

Hypoalgesia to A-delta fiber-mediated pain perception was not observed. Group-dependent hypoalgesia of temporal summation specific to the lumbar innervated region was observed. Pair-wise comparisons indicated significant hypoalgesia in participants who received SMT, but not in those who rode a stationary bicycle or performed low back extension exercises. Psychological factors did not significantly correlate with changes in temporal summation in participants who received SMT.

The Mechanisms of Manual Therapy in the Treatment of
Musculoskeletal Pain: A Comprehensive Model

Man Ther. 2009 (Oct); 14 (5): 531–538 ~ FULL TEXT

Prior studies suggest manual therapy (MT) as effective in the treatment of musculoskeletal pain; however, the mechanisms through which MT exerts its effects are not established. In this paper we present a comprehensive model to direct future studies in MT. This model provides visualization of potential individual mechanisms of MT that the current literature suggests as pertinent and provides a framework for the consideration of the potential interaction between these individual mechanisms.

Sympathetic and Parasympathetic Responses to Specific
Diversified Adjustments to Chiropractic Vertebral
Subluxations of the Cervical and Thoracic Spine

J Chiropractic Medicine 2008 (Sep); 7 (3): 86–93 ~ FULL TEXT

Diastolic pressure (indicating a sympathetic response) dropped significantly postadjustment among those receiving cervical adjustments, accompanied by a moderate clinical effect (0.50). Pulse pressure increased significantly among those receiving cervical adjustments, accompanied by a large effect size (0.82). Although the decrease in pulse pressure for those receiving thoracic adjustments was not statistically significant, the decrease was accompanied by a moderate effect size (0.66).

Immobilization Induces Changes in Presynaptic Control
of Group Ia Afferents in Healthy Humans

J Physiol. 2008 (Sep 1); 586 (Pt 17): 4121–4135 ~ FULL TEXT

Although the present study involved limb immobilization in able-bodied subjects, the findings may also be of clinical relevance. This is especially the case in relation to neurological disorders leading to physical inactivity. It is noteworthy that the findings of increased H-reflexes, decreased GABAergic presynaptic inhibition and decreased post-activation depression following immobilization to some extent matches the findings of previous studies in spastic patients and it is worth considering the effects of reduced physical activity in itself. As mentioned previously, it is possible that the decreased presynaptic inhibition and post-activation depression observed in patients with cerebral or spinal lesions may at least in part be a consequence of the disuse of motoneurons and Ia afferents.

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 that chronic vertebral hypomobility (fixation) at L4 through L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level. Morphological parameters that appear to be affected include synaptic curvature, type of postsynaptic profile, and perforations of the PSD. Additional more definitive studies are warranted, and the biologic significance of these finding should be investigated.

A Hypothesis of Chronic Back Pain: Ligament Subfailure Injuries
Lead to Muscle Control Dysfunction

European Spine Journal 2006 (May); 15 (5): 668–676 ~ FULL TEXT

A new hypothesis of chronic back pain based upon muscle system dysfunction due to ligament injuries is described. Subfailure injuries of the ligaments and embedded mechanoreceptors generate corrupted mechanoreceptor signals. Consequently, the neuromuscular control unit produces corrupted muscle response pattern, resulting in excessive loading and, possibly, injuries of the spinal structures, including additional injuries of the mechanoreceptors. The hypothesis accounts for many of the common and important experimental observations and clinical findings seen in low back pain and whiplash patients.

Cervical Spine Manipulation Alters Sensorimotor Integration:
A Somatosensory Evoked Potential Study

Clin Neurophysiol. 2007 (Feb); 118 (2): 391–402

Spinal manipulation of dysfunctional cervical joints can lead to transient cortical plastic changes, as demonstrated by attenuation of cortical somatosensory evoked responses.   This study suggests that cervical spine manipulation may alter cortical somatosensory processing and sensorimotor integration. These findings may help to elucidate the mechanisms responsible for the effective relief of pain and restoration of functional ability documented following spinal manipulation treatment.

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

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.

Biomechanical and Neurophysiological Responses to
Spinal Manipulation in Patients With
Lumbar Radiculopathy

J Manipulative Physiol Ther. 2004 (Jan); 27 (1): 1–15 ~ FULL TEXT

Because spinal manipulation (SM) is a mechanical intervention, it is inherently logical to assume that its mechanisms of therapeutic benefit may lie in the mechanical properties of the applied force (mechanical mechanisms), the body's response to such force (mechanical or physiologic mechanisms), or a combination of these and other factors. Basic science research, including biomechanical and neurophysiological investigations of the body's response to SM, therefore, should assist researchers, educators, and clinicians to understand the mechanisms of SM, to more fully develop SM techniques, to better train clinicians, and ultimately attempt to minimize risks while achieving better results with patients.

Neuromechanical Characterization Of In Vivo Lumbar
Spinal Manipulation. Part II.
Neurophysiological Response

J Manipulative Physiol Ther. 2003 (Nov); 26 (9): 579–591

Spinal manipulative thrusts resulted in positive electromyographic (EMG) and compound action potential (CAP) responses that were typically characterized by a single voltage potential change lasting several milliseconds in duration. However, multiple EMG and CAP discharges were observed in numerous cases. The temporal relationship between the initiation of the mechanical thrust and the neurophysiologic response to internal and external spinal manipulative therapy (SMT) thrusts ranged from 2.4 to 18.1 ms and 2.4 to 28.6 ms for EMG and CAP responses, respectively. Neurophysiologic responses varied substantially between patients. Vertebral motions and resulting spinal nerve root and neuromuscular reflex responses appear to be temporally related to the applied force during SMT. These findings suggest that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting physiologic responses.

Chiropractic Subluxation Assessment:
What the Research Tells Us

J Canadian Chiropractic Assoc 2002; 46 (4): 215–220 ~ FULL TEXT

When you speak of subluxation, the first description that often jumps to mind is the traditional misalignment, occlusion of a foramen, pressure on a nerve and interference (MOPI) model proposed by B.J. Palmer. [2] In fact there are several modern models currently in use as well. Some are conceptual models, such as the Vertebral Subluxation Complex model of Faye and Lantz, [2] which proposes as many as nine components interacting in a complex.

Neurophysiological Effects of Spinal Manipulation
Spine J (North American Spine Society) 2002 (Sep); 2 (5): 357–671 ~ FULL TEXT

Biomechanical changes caused by spinal manipulation are thought to have physiological consequences by means of their effects on the inflow of sensory information to the central nervous system. Muscle spindle afferents and Golgi tendon organ afferents are stimulated by spinal manipulation. Smaller-diameter sensory nerve fibers are likely activated, although this has not been demonstrated directly. Mechanical and chemical changes in the intervertebral foramen caused by a herniated intervertebral disc can affect the dorsal roots and dorsal root ganglia, but it is not known if spinal manipulation directly affects these changes.

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.

The Effects of Mild Compression on Spinal Nerve Roots
with Implications for Models of Vertebral Subluxation
and the Clinical Effects of Chiropractic Adjustment

J Vertebral Subluxation Research 2001 (May); 4 (2): 1–13

There is evidence of nerve compression at the level of the intervertebral foramen (IVF) occurring anywhere from 15.4% to 78% of levels inspected. Most of the spines inspected were already prescreened to eliminate those that were definitely known to have nerve compression problems. Pressures as little as 10 mm Hg can alter the nerve root and dorsal root ganglion’s abilities to function normally. In the normal range of motion the pressures generated in the IVF may exceed 30 mm Hg. When considering the concept of a joint fixated in a diminished sphere of its normal range of motion in conjunction with the mild pressure increases, it becomes apparent that nerve function can be significantly altered.

Response of Muscle Proprioceptors to Spinal Manipulative-like
Loads in the Anesthetized Cat

J Manipulative Physiol Ther. 2001 (Jan); 24 (1): 2–11 ~ FULL TEXT

The data suggest that the high-velocity, short-duration load delivered during the impulse of a spinal manipulation can stimulate muscle spindles and Golgi tendon organs more than the preload. The physiologically relevant portion of the manipulation may relate to its ability to increase as well as decrease the discharge of muscle proprioceptors. In addition, the preload, even in the absence of the impulse, can change the discharge of paraspinal muscle spindles. Loading of the vertebral column during a sham manipulation may affect the discharge of paraspinal proprioceptors.

Mechanical Force Spinal Manipulation Increases Trunk Muscle
Strength Assessed By Electromyography:
A Comparative Clinical Trial

J Manipulative Physiol Ther. 2000 (Nov); 23 (9): 585–595 ~ FULL TEXT

The results of this preliminary clinical trial demonstrated that MFMA SMT results in a significant increase in sEMG erector spinae isometric MVC muscle output. These findings indicate that altered muscle function may be a potential short-term therapeutic effect of MFMA SMT, and they form a basis for a randomized, controlled clinical trial to further investigate acute and long-term changes in low back function.

Neurophysiologic Response to Intraoperative
Lumbosacral Spinal Manipulation

J Manipulative Physiol Ther. 2000 (Sep); 23 (7): 447–457 ~ FULL TEXT

During the active trials, mixed-nerve root action potentials were observed in response to both internal and external spinal manipulative thrusts. Differences in the amplitude and discharge frequency were noted in response to varying segmental contact points and force vectors, and similarities were noted for internally and externally applied spinal manipulative thrusts. Amplitudes of mixed-nerve root action potentials ranged from 200 to 2600 mV for internal thrusts and 800 to 3500 mV for external thrusts.

Neurologic Effects of the Adjustment
J Manipulative Physiol Ther. 2000 (Feb); 23 (2): 112–114 ~ FULL TEXT

This paper discusses the several theories pertaining to the chiropractic adjustment, including the nerve compression theory, reflex theories, and pain relief theories. There is now sufficient scientific research to consider these theories reasonable working models to explain the effects of the adjustment but insufficient to consider them valid.

The Reflex Effects of Subluxation:
The Autonomic Nervous System

J Manipulative Physiol Ther 2000 (Feb); 23 (2): 104–106 ~ FULL TEXT

There is no shortage of theories to explain the role of subluxation in disease and the effect of adjustment in relieving symptoms. The autonomic nervous system has often been invoked in constructing mechanisms to account for the effects of spinal dysfunction; recent investigations justify the attention that has been focused on this component of the nervous system. Recent neuroscience research supports a neurophysiologie rationale for the concept that aberrant stimulation of spinal or paraspinal structures may lead to segmentally organized reflex responses of the autonomic nervous system, which in turn may alter visceral function.

Mechanisms of Neurovascular Compression Within the Spinal
and Intervertebral Canals

J Manipulative Physiol Ther 2000 (Feb); 23 (2): 107–111 ~ FULL TEXT

Stenosis of the spinal and intervertebral canal neurovascular structures can be caused by various bony and soft-tissue structures. Stenosis can be related to osteophytosis of the vertebral body, uncoverte-intervertebral disc protrusion, ossification of the posterior longitudinal ligament, and ligamentum flavum hypertrophy or buckling. nbsp; Various forms of spinal and intervertebral canal stenosis can cause compression of neurovascular structures that may, in turn, be responsible for symptomatology. Of course, autopsy findings cannot be equated with painful syndromes in patients.

The Somatosensory System of the Neck and its Effects
on the Central Nervous System

J Manipulative Physiol Ther. 1998 (Oct); 21 (8): 553–563

Studies involving human and nonhuman vertebrates have provided considerable information about the anatomy of the sensory receptors located in the neck and about where information from these receptors is relayed in the spinal cord and brain. Physiological experiments involving electrical and natural stimulation of the head and neck regions have identified a role for some of these receptors in neck-evoked reflexes. It is clear that in addition to signaling nociception, the somatosensory system of the neck may influence the motor control of the neck, eyes, limbs, respiratory muscles and possibly the activity of some preganglionic sympathetic nerves.

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.

Somatic Dysfunction and the Phenomenon of Visceral Disease Simulation:
A Probable Explanation for the Apparent Effectiveness of Somatic Therapy
in Patients Presumed to be Suffering from True Visceral Disease

J Manipulative Physiol Ther 1995 (Jul); 18 (6): 379–397

The proper differential diagnosis of somatic vs. visceral dysfunction represents a challenge for both the medical and chiropractic physician. The afferent convergence mechanisms, which can create signs and symptoms that are virtually indistinguishable with respect to their somatic vs. visceral etiologies, need to be appreciated by all portal-of-entry health care providers, to insure timely referral of patients to the health specialist appropriate to their condition. Furthermore, it is not unreasonable that this somatic visceral-disease mimicry could very well account for the "cures" of presumed organ disease that have been observed over the years in response to various somatic therapies (e.g., spinal manipulation, acupuncture, Rolfing, Qi Gong, etc.) and may represent a common phenomenon that has led to "holistic" health care claims on the part of such clinical disciplines.

Four Articles Which Describe the Relationship Between the
Upper Cervical Spine and Headaches and Chronic Head Pain

Thanks to Rick Hallgren

   Atrophy of Suboccipital Muscles in Chronic Pain Patients
We have observed previously unreported muscle atrophy in the rectus capitis posterior minor (RCPMI) muscles of a group of chronic pain patients. We hypothesize that chronic pain, in this select group of patients, is a consequence of tramua that occurs to the C1 dorsal ramus during whiplash.

Magnetic Resonance Imaging of the Upper Cervical Spine
We are currently using MRI to investigate the functional integrity of the upper cervical spine. We started out looking for hypertonic muscles in a population of patients who were suffering from chronic head and neck pain. My first task was to collect MRI data and to identify suboccipital muscles within the MR images. So I brought together a physician and an anatomy professor to see if they could help me out. Their comments were classic. The anatomy professor said, "The reason you can't find those muscles is because they are not there." The physician immediately responded by saying, "No wonder these patients don't get any better." I had been using images that were collected from a chronic pain patient, and it was apparent that the rectus capitis posterior minor muscles were missing. When we looked at images from a control subject it was very easy to locate these muscles. At that point, the focus of our research switched from looking for hypertonic muscles to comparing muscle density between the control group and the chronic pain group.

Anatomic Relation Between the Rectus Capitis
Posterior Minor Muscle and the Spinal Dura Mater

We observed that the PAO membrane was securely fixed to the surface of the dural tube by multitudinous fine connective tissue fibers. There was no real interlaminar space between these two structures and they appeared to function as a single entity. The influence of the RCPMI muscle on the dura mater was artificially produced in the hemisected specimen. Artificially functioning the muscle produced obvious movement of the spinal dura between the occiput and the atlas, and resultant fluid movement was observed to the level of the pons and cerebellum.

Visualization of the Muscle-Dural Bridge
in the Visible Human Female Data Set

Spine Journal 1995; 20 (23): 2484–2486

It has been speculated that the function of the muscle dural bridge may be to prevent folding of the dura mater during hyperextension of the neck. Also, clinical evidence suggests that the muscle dural bridge may play an important role the pathogenesis of the cervicogenic headaches.

The Neurophysiological Evaluation of the Subluxation Complex:
Documenting the Neurological Component with
Somatosensory Evoked Potentials

Chiropractic Research Journal 1994; 3 (1) ~ FULL TEXT

The results seen in this study indicate highly significant changes for the pre vs post adjustment SSEP tests. The mean latencies decreased after chiropractic adjustment in each of the nerves tested. This would seem to indicate that the upper cervical subluxation does cause neurological compromise in nerves forming both the brachial and lumbo-sacral plexuses. The removal of the subluxation by chiropractic adjustment results in improved conduction of the neural impulses as demonstrated on the post-adjustment tests. The improvements that were observed are similar to the changes seen when neurological compromise is relieved by surgical procedures to decompress or stabilize the spine.

How Does Subluxation Affect the Nervous System?
Dynamic Chiropractic (October 7, 1996)

In 1976, Drs. Vert Mooney and James Robertson set out to confirm the earlier research on referred pain and discussed their findings in a well-known paper, "The Facet Syndrome." [3] Their attention was directed toward the facet joints rather than spinal muscles and ligaments. The subjects in this study included five normal individuals and 15 patients with low back pain. To make a semi-long story short, Mooney and Robertson discovered that, indeed, injecting hypertonic saline into facet joints resulted in local and referred pain. They also discovered that, "slightly increasing the volume of injection would consistently increase the amount of pain radiation."

Nociception, Mechanoreception and Proprioception:
What's the Difference and What Do They Have
to Do with Subluxation?

Dynamic Chiropractic (November 18, 1994)

Nociception is the process by which nociceptive receptors receive tissue damaging stimuli that is then carried into the CNS by nociceptive axons (A-delta and C fibers). Potential outcomes of nociceptive input to the cord include pain, autonomic symptoms, vasoconstriction and muscle spasm. Nociceptive input to the cord appears to be the driving force behind the pathogenesis of subluxation (see Figure A). We must remember that nociception and pain are two completely different animals. However, a devastating consequence of both pain and nociceptive stimulation of the hypothalamus, is the release of cortisol by the adrenal glands. Over time, elevated levels of cortisol will promote glucose intolerance, inhibit collagen formation, increase protein breakdown, inhibit secretory IgA output, and inhibit white blood cell function. Clearly, the clinical importance of pain and nociception should not be minimized.

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