The effects of side-posture positioning and spinal adjusting on the lumbar Z joints - A randomized controlled trial with sixty-four subjects

Study Design: A blinded, randomized controlled trial was conducted. Objective: To test the hypothesis that chiropractic side-posture manipulation (adjusting) of the lumbar spine separates (gaps) the zygapophysial (Z) joints. Summary of Background Data: Spinal adjusting is thought to gap the Z joints, yet no studies have conclusively validated this hypothesis, and some investigators have reported that the lumbar Z joints do not gap during rotation. Methods: For this study, 64 healthy student volunteers (32 men and 32 women) ages 22 to 30 years with no history of significant low back pain were randomized into four groups of 8 men and 8 women each. Interventions included lumbar side-posture spinal adjusting (manipulation) and side-posture positioning. 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 spinal positioning were compared. Results: Observers performing the measurements were blinded as to group first and second scans. Reliability of the measurements was established. Differences were found between the groups (F = 24.15; P < 0.000, analysis of variance). Side-posture positioning showed greater gapping than the control condition (mean difference; 1.18; P < 0.000), side-posture adjusting showed greater gapping than the control condition (mean difference, 1.89; P < 0.000), and side-posture adjusting showed greater gapping than side-posture positioning (mean difference, 0.71; P = 0.047). Conclusions: Spinal adjusting produced increased separation (gapping) of the Z joints. Side-posture positioning also produced gapping, but less than that seen with lumbar side-posture adjusting. This study helps to increase understanding about the mechanism of action for spinal manipulation.