Spine (Phila Pa 1976). Author manuscript; available in PMC 2012 Oct 1.
Published in final edited form as:
Spine (Phila Pa 1976). 2011 Oct 1; 36(21): 1772–1781.
doi: 10.1097/BRS.0b013e318216337d
PMCID: PMC3150636
NIHMSID: NIHMS282545
PMID: 21358568
Preliminary investigation of the mechanisms underlying the effects of manipulation: exploration of a multi-variate model including spinal stiffness, multifidus recruitment, and clinical findings
Julie M. Fritz, PhD, PT, Associate Professor
Abstract
Study Design
Prospective case series.
Objective
Examine spinal stiffness in subjects with low back pain (LBP) receiving spinal manipulative therapy (SMT), evaluate associations between stiffness characteristics and clinical outcome, and explore a multi-variate model of SMT mechanisms as related to effects on stiffness, lumbar multifidus (LM) recruitment and status on a clinical prediction rule (CPR) for SMT outcomes.
Summary of Background Data
Mechanisms underlying the clinical effects of SMT are poorly understood. Many explanations have been proposed, but few studies have related potential mechanisms to clinical outcomes or considered multiple mechanisms concurrently.
Methods
Subjects with LBP were treated with 2 SMT sessions over 1 week. CPR status was assessed at baseline. Clinical outcome was based on the Oswestry disability index (ODI). Mechanized indentation measures of spinal stiffness and ultrasonic measures of LM recruitment were taken before and after each SMT, and after 1 week. Global and terminal stiffness were calculated. Multivariate regression was used to evaluate the relationship between stiffness variables and percentage ODI improvement. Zero-order correlations among stiffness variables, LM recruitment changes, CPR status, and clinical outcome were examined. Path analysis was used to evaluate a multi-variate model of SMT effects.
Results
Forty-eight subjects (54% female) had complete stiffness data. Significant immediate decreases in global and terminal stiffness occurred post-SMT regardless of outcome. ODI improvement was related to greater immediate decrease in global stiffness (p=0.025), and less initial terminal stiffness (p=0.01). Zero-order correlations and path analysis supported a multi-variate model suggesting clinical outcome of SMT is mediated by improvements in LM recruitment and immediate decrease in global stiffness. Initial terminal stiffness and CPR status may relate to outcome though their relationship with LM recruitment.
Conclusions
The underlying mechanisms explaining the benefits of SMT appear to be multi-factorial. Both spinal stiffness characteristics and LM recruitment changes appear to play a role.