• G D Cramer, N R Tuck, J T Knudsen, S D Fonda, J S Schliesser, J T Fournier, and P Patel.
• Department of Research, the National College of Chiropractic, Lombard, IL 60148, USA.
• J Manipulative Physiol Ther. 2000 Jul 1;23(6):380-94.

ObjectiveTo 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.DesignBefore and after study with randomization.SettingChiropractic college clinic and magnetic resonance imaging (MRI) facility.ParticipantsSixteen 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.InterventionsLumbar side-posture spinal adjusting (manipulation) and side-posture positioning.Main Outcome MeasuresComparison 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 ResultsObservers 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).ConclusionsLumbar 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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