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

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

This section is compiled by Frank M. Painter, D.C.
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FROM:   Chiropractic Research Journal 1994; 3 (1) ~ FULL TEXT

Karen Feeley Collins, B.A., D.C.
Bruce Pfleger, Ph.D.

The Abstract:

Somatosensory evoked potential (SSEP) testing is a non-invasive, objective procedure, which achieves a high degree of sensitivity and specificity for identifying neurological insult. The purpose of this study was to: 1) use this test to validate the neurological component of the subluxation complex and 2) confirm the removal or decrease of neurologic compromise as a result of the chiropractic adjustment.

The initial SSEP evaluations revealed neurological insult in 93% of the patients in this study. Eighty-five percent of patients with documented deficits of the sensory nervous pathways were shown to have significantly improved SSEP waveforms on post-adjustment evaluation. These changes in waveforms were consistent with improvement or elimination of the varying subjective complaints.

The FULL TEXT Article


Since the original work of D. D. Palmer, chiropractic has had as its goal the reduction of the vertebral subluxation through chiropractic adjustment. Historically, the vertebral subluxation consists of two components: biomechanical and neurological. While the biomechanical component has been quantitatively and qualitatively assessed, the neurological component has only been observed indirectly through electromyography, thermography and clinical methodology.

Somatosensory evoked potential testing (SSEP) has been successfully utilized in clinical medicine for the past twenty years. Evoked potentials are used to evaluate the functioning of the sensory neural pathways. The validity, reliability and sensitivity of SSEP exams have been well documented. [1-4] These tests are often used in the operating room to monitor the functional integrity of the neurological pathways during surgical procedure [5-10] and to determine the effectiveness of the surgical procedure. [5, 11-14]

The purpose of this study was to determine what kind of changes, if any, could be seen in the evoked potential waveforms as a result of the subluxation complex. SSEP waveforms were evaluated for changes in latency and amplitude before and during chiropractic care.


Patients entering the Sid E. Williams Research Center with radiating pain, numbness or paresthesia were included in this study. Orthopedic, neurological and chiropractic examination were done on each patient in accordance with Life College clinic guidelines. Cervical x-rays were taken, including lateral, nasium, vertex and A-P lower cervical views. In addition to the standard exams, patients were evaluated using somatosensory evoked potential tests according to the Glick protocol. [15] SSEP testing was performed prior to the first adjustment and then four to eight weeks after. The Cadwell Excell signal averaging evoked potential instrument was used for all SSEP tests. Depending on which extremity the patients were experiencing problems with, nerves of the brachial or lumbo-sacral plexus were evaluated. A total of fourteen patients were evaluated in this investigation. Nine individuals had chronic low back pain with pain or paresthesia radiating into the leg and five patients had problems involving the upper extremity (1 thoracic outlet syndrome, 2 frozen shoulders, and 2 cervicobrachialgias). Latencies were measured bilaterally from three upper extremity nerves (median, ulnar and superficial sensory radial). Lower extremity SSEP testing was done bilaterally on five sacral plexus nerves (posterior tibial, sural, superficial peroneal, saphenous and the common peroneal). Responses to the peripheral stimuli were measured at the cortex.

All patients had clinical indications of an upper cervical misalignment on initial exam. Analysis of the x-rays was done by either the Grostic or Sweat upper cervical analysis. [16, 17] Management of these patients was strictly through upper cervical techniques with the adjustments delivered by either the Life Cervical, Laney or Sweat instruments.


Every patient, except one (93%), had observable abnormalities of the pre-adjustment SSEP waveforms. Eighty-five percent of patients with documented neurological insult on initial SSEP assessments were shown to have significantly improved waveforms on the post-adjustment evaluation. (Figures 1-9 UNAVAILABLE) Improvements were generally seen as decrease in latencies (or increase in nerve conduction velocities), increased amplitude and improved coherence or definition of the cortical wave forms. The changes reflected on these tests were consistent with improvement or elimination of the varying subjective complaints. (See glossary for further explaination.)

Pre and post adjustment cortical latencies were first examined for the bilateral data grouped together, providing an N of 10 for the upper extremity nerves and an N of 16 for the lower extremity nerves. Mean latencies decreased after chiropractic adjustment in each of the eight nerves, ranging from a 1.62% reduction in the superficial sensory radial nerve to an 11.6% reduction in the common peroneal nerve.

A multivariate factorial analysis of variance (MANOVA) was performed on both the upper and lower extremity data. Parameters for the upper extremity data included Nerve [3] by Side [L/R] by Test [pre/post]. Results indicated highly significant findings for the pre vs post test on the upper extremity nerves (F = 45.91, p = 0.002). Similarly, parameters for the lower extremity data included Nerve [5] by Side [L/R] by Test [pre/post]. Results for pre vs post test were again significant (F = 5.76, p = 0.047). Results were not significant for laterality in either the upper or lower extremity data.


SSEP testing is used routinely to diagnose the integrity of a specific sensory neural pathway. These tests provide an objective measure to document and localize interruption or delay of sensory neural conduction, through both the peripheral and central nervous systems. This type of testing is commonly used to determine whether a particular surgical procedure, such as decompression and stabilization of the spine, has been effective and to ensure that somatosensory function is not impaired during surgery. [5, 7-12] These exams are also practical to gain further information to support diagnoses such as spinal stenosis, [18, 19] disc disease [14, 20-22] and radiculopathies. [20] For a nerve to be considered abnormal there should be an increase in latency of at least 3 msec when compared to the contralateral nerve or a large decrease in amplitude. [14, 18, 20-22]

It is easy to see the clinical utility of SSEP testing as it relates to chiropractic and our premise that vertebral subluxations cause neurological compromise. The first chiropractic study utilizing SSEP testing was published in 1982. [23] These investigators observed distinct modification of the first positive peak latencies before and after chiropractic adjustment on patients with cervicobrachial, lumbar and sciatic pain. The follow up testing was done one year after the initiation of the chiropractic care plan. The average latency decrease was 8-9 msec. More research evaluating the effectiveness of chiropractic using SEP's was published in 1990. [24] This study, which included a control group, measured the SSEP tests immediately after spinal adjustments or massage with light traction. An average decrease of 1.29 msec was seen in the adjusted group, while the control group had an average decrease of 0.60 msec in cortical latencies. In 1992 and 1993, Dr. Glick presented his findings on pre and post adjustment SEP testing at the International Conference on Spinal Manipulation. [25, 26] In his investigation there were also significant improvements noted from the pre to post adjustment SSEP tests, noted as either a decrease in cortical latencies, improved coherence or increase in wave amplitudes. Another study demonstrated how paraspinal muscle evoked cerebral potentials, elicited by magnetic stimulation, may have potential for quantitative evaluation of muscle spasm in low back pain. [27] These investigator s show a correlation between decreased amplitude of the waveforms and the presence of muscle spasm, with the potentials returning to normal after the application of osteopathic spinal manipulation.


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.


Many thanks to everyone involved with this project, especially the student clinicians who cared for these patients. This research was funded by the Sid E. Williams Research Center and the Cadwell Corporation who donated the equipment necessary for SSEP testing. We would also like to thank Atlanta x-ray and Alice Reed for the use of their x-ray equipment and support of Chiropractic Research.


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