The aim of this study was to determine if low back pain (LBP) patients who respond to spinal manipulative therapy (SMT) differ biomechanically from non-responders and untreated asymptomatic controls. Some, but not all LBP patients report improvement in function after SMT. When compared to non-responders, studies suggest that SMT-responders exhibit significant changes in spinal stiffness, muscle contraction and disc diffusion. Unfortunately, the significance of these observations remains uncertain given methodological differences between studies including a lack of controls. LBP participants and asymptomatic controls attended three sessions over 7 days. On sessions 1 and 2, LBP participants received SMT (+LBP/+SMT, n = 32) while asymptomatic controls did not (-LBP/-SMT, n = 57). In these sessions, spinal stiffness and multifidus thickness ratios were obtained prior to and following SMT and on day 7. Apparent diffusion coefficients (ADC) from lumbar discs were obtained from +LBP/+SMT participants before and after SMT on session 1 and from a LBP control group that did not receive SMT (+LBP/-SMT, n = 16). +LBP/+SMT participants were dichotomized as responders/non-responders based on self-reported disability on day 7. A repeated measures ANCOVA was used to compare ADCs among responders, non-responders and +LBP/SMT, as well as spinal stiffness or multifidus thickness ratio among responders, non-responders and -LBP/-SMT subjects. After the first SMT, SMT-responders displayed statistically significant decreases in spinal stiffness and increases in multifidus thickness ratio sustained over 7 days; these findings were not observed in other groups. Similarly, only SMT-responders displayed significant post-SMT improvement in ADC.
Those reporting post-SMT improvement in disability showed simultaneous changes between self-reported and objective measures of spinal function. This coherence was not observed in asymptomatic controls or no-treatment controls. These data imply that SMT impacts biomechanical characteristics within SMT-responders not present in all LBP patients. This work provides a foundation to investigate the heterogeneous nature of LBP, mechanisms underlying differential therapeutic response and the biomechanical and imaging characteristics defining responders at baseline.