Morphometric differences of cavitating Z joints

A previous study of 40 subjects undergoing spinal manipulative therapy (SMT) assessed cavitation measured by accelerometry and L3/L4 – L5/S1 zygapophysial (Z) joint space separation (gapping) measured from MRI scans. An unexpected (and previously unreported) finding was that 6 joints cavitated multiple times. Methods We performed an IRB‐approved comparative study (n=18) assessing morphometric analysis of multiple‐cavitating (MC), single‐cavitating (SC), and non‐cavitating (NC) Z joints (joints matched for segmental level, side, and gender). The medial, central, and lateral aspects of the Z joint spaces were measured from pre‐SMT MRI scans. Group comparisons using the Kruskal‐Wallis Test were made for the measurements from the 3 locations and the total of the 3 measurements (total measurement = TM, the primary outcome). Results TM and medial joint space were smaller/narrower for the MC group (TM, p=0.008; medial, p=0.04). No differences were found for the central and lateral joint spaces (central, p=0.18; lateral, p=0.29). Conclusions Multiple cavitations during SMT may be related to the “close packed” nature of a joint in the neutral position (particularly the medial aspect of the joint). These findings provide information about the characteristics of Z joints cavitating during SMT. Funding: NIH/NCCAM Grant # 3R01AT000123‐06S2.