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.

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Objective The purpose of this study was to quantify lumbar zygapophyseal (Z) joint space separation (gapping) in low back pain (LBP) subjects after spinal manipulative therapy (SMT) or side-posture positioning (SPP). Methods This was a controlled mechanisms trial with randomization and blinding. Acute LBP subjects (N=112, four n=28 MRI protocol groups) had 2 magnetic resonance imaging (MRI) appointments (initial enrollment [M1] and following 2 weeks of chiropractic treatment [M2]; receiving 2 MRI scans of the L4/L5 and L5/S1 Z joints at each MRI appointment. After the first MRI scan of each appointment, subjects were randomized (M1 appointment) or assigned (M2 appointment) into SPP (non-manipulation), SMT (manipulation), or control MRI protocol groups. After SPP or SMT, a second MRI was taken. The central anterior-posterior (A-P) joint space was measured. Difference between most painful side A-P measurements taken post- and pre-intervention was the Z joint “gapping difference.” Gapping differences were compared (ANOVA) among protocol groups. Secondary measures of pain visual analog scale (VAS), verbal numeric pain rating scale (VNPRS), and function Bournemouth questionnaire (BQ) were assessed. Results Gapping differences were significant at the first (adjusted, p=0.01; SPP=0.66 +0.48mm; SMT=0.23 +0.86; control=0.18 +0.71) and second (adjusted, p=0.0005; SPP=0.65 +0.92mm, SMT=0.89 +0.71; control=0.35 +0.32) MRI appointments. VNPRS differences were significant at first MRI appointment (p=0.04) with SMT showing the greatest improvement. VAS and BQ improved after two weeks of care in all groups (both p<0.0001). Conclusions SPP showed greatest gapping at baseline. After two weeks, SMT resulted in greatest gapping. SPP appeared to have additive therapeutic benefit to SMT.

Purpose This IRB-approved project determined the feasibility of conducting larger studies assessing the relationship between cavitation and zygapophysial (Z) joint gapping following spinal manipulative therapy (SMT). Methods Five healthy volunteers (average age 25.4 years) were screened and examined against inclusion and exclusion criteria. High signal MRI markers were fixed to T12, L3, and S1 spinous processes. Scout images were taken to verify the location of the markers. Axial images of the L4/L5 and L5/S1 levels were obtained in the neutral supine position. Following the first MRI, accelerometers were placed over the same spinous processes and recordings were made from them during side-posture positioning and SMT. The accelerometers were removed and each subject was scanned in side-posture. The greatest central A-P Z joint spaces (gap) were measured from the first and second MRI scans. Values obtained from the first scan were subtracted from those of the second, a positive result indicating an increase in gapping following SMT (positive gapping difference). Gapping difference was compared between the up-side (SMT) joints vs. the down-side (non-SMT) joints and between up-side cavitation vs. up-side non-cavitation joints. Results Greater gapping was found in Z joints that received SMT (0.5 ±0.6 mm) vs. non-SMT joints (−0.2 ±0.6 mm), and vertebral segments that cavitated gapped more than those that did not cavitate (0.8 ±0.7 mm vs. 0.4 ±0.5 mm). Conclusions A future clinical study is quite feasible. Forty subjects (30 SMT and 10 Control) would be needed for appropriate power (0.90). Partial funding by NIH/NCCAM (#2R01AT000123).

Objectives The purpose of this study was to use previously validated methods to quantify and relate 2 phenomena associated with chiropractic spinal manipulative therapy (SMT): 1) cavitation and 2) the simultaneous gapping (separation) of the lumbar zygapophyseal (Z) joint spaces. Methods This was a randomized, controlled, mechanistic clinical trial with blinding. Forty healthy subjects (18 to 30 years of age) without a history of low back pain participated. Seven accelerometers were affixed to the skin overlying the spinous processes of L1-L5 and the S1 and S2 sacral tubercles. Two additional accelerometers were positioned 3 cm left and right lateral to the L4/L5 inter-spinous space. Subjects were randomized into: Group 1–side-posture SMT (n=30) or Group 2–side-posture positioning (SPP, n=10). Cavitations were determined by accelerometer recordings during SMT and SPP (left-side=up-side for both groups); gapping (gapping difference) was determined by the difference between pre- and post-intervention MRI joint space measurements. Results of mean gapping differences were compared. Results Up-side SMT and SPP joints gapped more than down-side joints (0.69 vs. −0.17mm, p<0.0001). SMT up-side joints gapped more than SPP up-side joints (0.75 vs. 0.52mm, p=0.03). SMT up-side joints gapped more in males than females (1.01 vs. 0.49mm, p<0.002). Overall, joints that cavitated gapped more than those that did not (0.56vs. 0.22mm, p=0.01). No relationship was found between the occurrence of cavitation and gapping with up-side joints alone (p=0.43). Conclusions Z joints receiving chiropractic SMT gapped more than those receiving side-posture positioning alone, Z joints of males gapped more than those of females, and cavitation indicated that a joint had gapped, but not how much a joint had gapped.