Background The McKenzie Method of Mechanical Diagnosis and Therapy (MDT) is one of the exercise approaches recommended by low back pain (LBP) guidelines. We investigated the efficacy of MDT compared with placebo in patients with chronic LBP.

Methods This was a prospectively registered, two-arm randomised placebo controlled trial, with a blinded assessor. A total of 148 patients seeking care for chronic LBP were randomly allocated to either MDT (n=74) or placebo (n=74). Patients from both groups received 10 treatment sessions over 5 weeks. Patients from both groups also received an educational booklet. Clinical outcomes were obtained at the end of treatment (5 weeks) and 3, 6 and 12 months after randomisation. Primary outcomes were pain intensity and disability at the end of treatment (5 weeks). We also conducted a subgroup analysis to identify potential treatment effect modifiers that could predict a better response to MDT treatment.

Results The MDT group had greater improvements in pain intensity at the end of treatment (mean difference (MD) −1.00, 95% CI −2.09 to −0.01) but not for disability (MD −0.84, 95% CI −2.62 to 0.93). We did not detect between-group differences for any secondary outcomes, nor were any treatment effect modifiers identified. Patients did not report any adverse events.

Conclusion We found a small and likely not clinically relevant difference in pain intensity favouring the MDT method immediately at the end of 5 weeks of treatment but not for disability. No other difference was found for any of the primary or secondary outcomes at any follow-up times.

Trial registration number ClinicalTrials.gov (NCT02123394)