Chronic primary low back pain (CPLBP) refers to low back pain that persists over three months, that cannot be explained by another chronic condition, and that is associated with emotional distress and disability. Previous studies have shown that spinal manipulative therapy (SMT) is effective to relieve CPLBP, but the underlying mechanisms remain elusive. This randomized placebo-controlled dual-blind mixed experimental trial (NCT05162924) aimed to investigate the efficacy of SMT to improve CPLBP and its underlying mechanisms. Ninety-eight individuals with CPLBP and 49 controls were recruited. Individuals with CPLBP received SMT (n=49) or a control intervention (n=49), twelve times over four weeks. The primary outcomes were CPLBP intensity (0-100 on a numerical rating scale) and disability (Oswestry Disability Index). Secondary outcomes included pressure pain thresholds in four body regions, pain catastrophizing, central sensitization inventory, depressive symptoms, and anxiety scores. Individuals with CPLBP showed widespread mechanical hyperalgesia (p<.001) and higher scores for all questionnaires (p<.001). SMT reduced pain intensity compared with the control intervention (mean difference: -11.7 [95% CI, -11.0 to -12.5], p=.01), but not disability (p=.5). Similar mild to moderate adverse events were reported in both groups. Mechanical hyperalgesia at the manipulated segment was reduced after SMT compared with the control intervention (p<.05). Pain catastrophizing was reduced after SMT compared with the control intervention (p<.05), but this effect was not significant after accounting for changes in clinical pain. Although the reduction of segmental mechanical hyperalgesia likely contributes to the clinical benefits of SMT, the role of pain catastrophizing remains to be clarified.

PERSPECTIVE

This randomized controlled trial found that twelve sessions of spinal manipulative therapy yield greater relief of chronic primary low back pain than a control intervention. These clinical effects were independent of expectations, and accompanied by an attenuation of hyperalgesia in the targeted segment and a modulation of pain catastrophizing.