OBJECTIVE: To test the a priori hypothesis that one of the positive mechanisms of action of chiropractic side-posture manipulation (adjusting) of the lumbar spine is to separate, or gap, the zygapophysial (Z) joints. DESIGN: Before and after study with randomization. SETTING: Chiropractic college clinic and magnetic resonance imaging (MRI) facility. PARTICIPANTS: Sixteen healthy student volunteers (8 men and 8 women) ages 22 to 29 years with no history of significant low back pain. Nineteen volunteers were screened, with 3 disqualified from the study. Subjects were randomized into 4 groups, each with 2 men and 2 women. INTERVENTIONS: Lumbar side-posture spinal adjusting (manipulation) and side-posture positioning. MAIN OUTCOME MEASURES: Comparison of anterior to posterior measurements of the Z joints from MRI scans taken before and after side-posture spinal adjusting and before and after side-posture positioning, and a rigorous subjective evaluation protocol of the Z joints by 3 radiologists blinded to the randomized groups. MAIN RESULTS: Observers making measurements were blinded to what group subjects were placed in and whether they were measuring first or second scans; radiologists were blinded to what group subjects were assigned. Differences were found between the groups. Those receiving side-posture spinal adjusting and remaining in side posture showed the greatest increase in gapping (0.7 mm vs 0.0 mm for controls). CONCLUSIONS: Lumbar side-posture spinal adjusting produced increased separation (gapping) of the zygapophysial joints. Side-posture positioning also produced gapping, but less than that seen with lumbar side-posture adjusting. A larger clinical trial should be performed to further define the results of this study.
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Cramer et al. (2000) studied this question.
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