Per J. Palmgren, DC, Peter J. Sandström, DC, Fredrik J. Lundqvist, DC,
Hannu Heikkilä, MD, PhD
Department of Research,
Scandinavian College of Chiropractic,
OBJECTIVE: The objective of this study was to examine alteration in head repositioning accuracy (HRA), range of motion, and pain intensity in patients with chronic cervical pain syndrome without a history of cervical trauma.
METHODS: The study was a prospective, randomized, controlled trial. Forty-one patients with chronic cervical pain were randomly assigned to either a control group or a chiropractic treatment group. All patients were clinically examined, given general information on cervical pain, and provided with training instructions based on the clinical evaluation. The treatment included sessions with high-velocity and low-amplitude manipulation, proprioceptive neuromuscular facilitation, ischemic compression of myofascial trigger points, and spinal rehabilitation exercises aiming to normalize cervical range of motion (CROM) and HRA. Subjective pain intensity, cervical kinesthetic sensibility, and CROM were recorded before and after the study period.
RESULTS: There was no difference between the treatment patients and the control subjects at the beginning with regard to age, sex, subjective pain intensity, range of motion, and HRA. At the 5-week follow-up, the treatment patients showed significant reductions in pain and improvement of all HRA aspects measured whereas the control subjects did not show any reduction in pain and improvement in only one HRA aspect. No significant difference was detected in CROM.
CONCLUSION: The results of this study suggest that chiropractic care can be effective in influencing the complex process of proprioceptive sensibility and pain of cervical origin. Short, specific chiropractic treatment programs with proper patient information may alter the course of chronic cervical pain.
From the Full-Text Article:
This study is relatively small (n = 20 in each group) but has an appropriate control and randomization procedure. Furthermore, only a few measurements have been done (subjective pain intensity, range of motion, and HRA). The results still indicate a positive outcome for patients receiving chiropractic treatment, with improvement of cervical kinesthetic functions and reduction of cervical pain. The treatment group significantly decreased their pain, measured with VAS, by the order of 29 mm, a noteworthy improved pain situation. No significant difference was observed in the active, biomechanically based CROM. However, in the proprioception-based HRA test, the treatment group showed significantly improved results in all assessed aspects whereas the control group showed improvement in only 1 of 6 aspects.
The present study does not explain by which mechanisms chiropractic treatment exerts its effects but gives an indication that it could be related to proprioceptive functions rather than by direct changes of biomechanical factors such as range of motion. Speculations can be made on which aspects of the chiropractic treatment could be responsible for the effect. Ischemic compression treatment of trigger points and proprioceptive neuromuscular facilitation mainly affect the more superficial muscles that proportionally have less-developed proprioceptive afferents.  The data from this study cannot reveal whether any significant effect was experienced at the level of deep interarticular muscles or whether trigger-point treatment may conceivably isolate these muscles in all of their intricate planes. Chiropractic manipulation, on the other hand, is believed to have its effect on the joints and the adjacent tissues.  A high-velocity and low-amplitude manipulative thrust in the plane of main movement of a joint is likely to affect also the profound interarticular muscles. Because the interventions in this study were concentrated to the muscles and articulations of the neck, it is likely that the observed effects were related to changes in mechanoreceptor afferent input rather than to changes in the vestibular system. Earlier studies have shown the presence of mechanoreceptive and nociceptive nerve endings in cervical facet capsules. Thus, these tissues can be monitored by the central nervous system and neural input from the facets is likely to be significant for proprioception along with pain sensation in the cervical spine.  The deep muscles of the vertebral column, predominantly those of the upper cervical complex, are arranged in a diversity of orientations. Deep muscles of the cervical spine have higher concentrations of mechanoreceptors in areas flanking the articulations than in the more superficial areas.  Signals from muscle receptors in individual neck muscles or muscle subsections may have a substantial potential to provide a detailed representation of head position and head movement.
A theory presented by Johansson and Sojka  suggests which mechanisms may be implicated in the source and dissemination of muscular tension. Increased muscle spindle sensitivity may be mediated by the sympathetic nervous system acting on the intrafusal fibers of the muscle spindles as a feedback loop. The correlation between interneurons and motor neurons in the spinal cord may also contribute to increased muscle tension. Assuming increased muscle tension and sensitized muscle spindles, the latter condition may give rise to erroneous proprioceptive signaling, particularly if spindles in dissimilar neck muscles or on different sides of the neck are disproportionately sensitized. Erroneous cervical proprioceptive information converges in the central nervous system with vestibular and visual signals, which could affect the mental perception of body orientation and lead to a misinterpretation of relation to the surrounding.
The method used for evaluating and measuring cervicocephalic kinesthetic sensibility is relatively simple to perform and reproducible and can therefore be used in scientific investigations aiming to identify certain subgroups with neck and shoulder pain. Kristjansson et al  compared 5 cervicocephalic relocation tests in 3 different subject groups in a case-control study and found that the HRA method introduced by Revel et al15 was the most reliable one for disclosing relocation inaccuracy among patients with neck pain. Subgroups categorized and classified objectively according to proprioceptive or nonproprioceptive etiology could thus be the focus of further studies. Further studies could also reveal if the techniques used here could be a valuable tool in daily chiropractic care.
The results of this study support that chiropractic care can be effective in influencing the complex process of proprioceptive sensibility and pain of cervical origin. Relocation dysfunction could be improved in subjects with nontraumatic neck pain. Similar conclusions were drawn by Karlberg et al  and Heikkilä and Wenngren ; this suggests that changes in the quality of proprioceptive information from the cervical spine region may affect postural control as well as reduction of cervical pain.