• Henderson CNR
• Owens EF Jr
• Pickar JG
• Gudavalli R

• Association of Chiropractic Colleges / congresses

METHODS: This study was reviewed and approved by the Institutional Review Board of the Palmer College of Chiropractic. Participants were volunteers from the student population of a chiropractic college, and were screened for incidence of cervical abnormalities. An electrogoniometer was used to measure head position, with a laser pointer used to relocate neutral head position between protocols. A force transducer measured the force of a maximum voluntary contraction with the neck extended 20° or left laterally flexed 25°. Each test began with location of neutral head position with participants’ eyes closed. The experimental protocol consisted of a deconditioning sequence of 5 head nods, followed by 1 of 3 conditioning sequences: a “No Hold” conditioning sequence where participants immediately repositioned their heads to neutral; a “Passive Hold” conditioning sequence where participants extended or laterally flex their necks and maintained that position for 10 seconds; an “Active Hold” conditioning sequence which was identical to Passive Hold and in addition participants contracted their neck muscles for 10 seconds to at least 70% maximum voluntary contraction. Following each conditioning sequence, participants resumed their perceived neutral target position. The difference between the initial and final head orientation was calculated in 3 orthogonal planes and used as a measure of proprioceptive error. ANOVA was used to account for variation between participants and to detect differences in proprioceptive error among the 3 conditioning sequences. Post-hoc tests (alpha level 0.05) were used for pair-wise comparisons.

RESULTS: Forty-eight students participated (36 males and 12 females, aged 28.2 ± 4.8 yrs). During the 20° neck extension test, No Hold and Passive Hold conditioning sequences, evoked AP flexion overshoots of the neutral target position were not statistically different from each other. By contrast, the Active Hold conditioning sequence evoked undershoot of the target position that was significantly different by 2.1°when compared with the other conditioning sequences. During the 25° lateral flexion test, the 3 conditioning sequences produced no differences in repositioning to the neutral target within the same plane as the test.

DISCUSSION: The main goal of this project was to investigate a proprioceptive task as an evaluative tool in the cervical spine. We found a statistically significant difference in repositioning error in AP-flexion during the extension task after isometric muscle contraction for 10 seconds, suggesting that the recent history of cervical paraspinal muscle contraction can influence the ability of participants to reposition their heads to a predetermined target. The condition of muscle shortening by resting the head in an extended position for 10 seconds did not show a different repositioning error from control. Since we were able to elicit a repositioning error in these normal, healthy student volunteers, it raises the question of whether patients with neck pain or signs of vertebral subluxation might show different repositioning errors in terms of magnitude or direction. Patients with vertebral fixation or relative segmental inflexibility might be more prone to the effects of muscle thixotropy and show repositioning errors in response to both the Passive Hold and Active Hold conditions. Our next step will be to assess repositioning errors in a population showing clinical signs of joint dysfunction in the neck.

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