Study design: Prospective case series.
Objective: To examine the relation between improved disability and changes in abdominal and lumbar multifidus (LM) thickness using ultrasound imaging following spinal manipulative therapy (SMT) in patients with low back pain (LBP).
Background: Although there is a growing body of literature demonstrating physiologic effects following the application of SMT, few studies have attempted to correlate these changes with clinically relevant outcomes.
Methods: Eighty-one participants with LBP underwent 2 thrust SMT treatments and 3 assessment sessions within 1 week. Transversus abdominis (TrA), internal oblique (IO), and LM muscle thickness was assessed during each session, using ultrasound imaging of the muscles at rest and during submaximal contractions. The Modified Oswestry Disability Index was used to quantify participants' improvement in LBP-related disability. Stepwise hierarchical multiple linear regression and repeated-measures analysis of variance were performed to examine the multivariate relationship between change in muscle thickness and clinical improvement over time.
Results: After controlling for the effects of age, sex, and body mass index, change in contracted LM muscle thickness was predictive of improved disability at 1 week (P = .02). As expected, larger increases in contracted LM muscle thickness at 1 week were associated with larger improvements in LBP-related disability. Contrary to our hypothesis, significant decreases in both contracted TrA and IO muscle thickness were observed immediately following SMT; but these changes were transient and unrelated to whether participants experienced clinical improvements.
Conclusion: These findings provide evidence that clinical improvement following SMT is associated with increased thickening of the LM muscle during a submaximal task.
Level of evidence: Prognosis, level 4.