“Mechanical Diagnosis and Therapy (MDT)” also known as McKenzie method like other interventions for low back pain (LBP) has been found to have small effects for people with LBP. It is possible that a group of patients respond best to MDT and have larger effects. Identification of patients who respond best to MDT compared to other interventions would be an important finding. This study was a secondary analysis of data from a previous trial comparing MDT to Back School in 148 patients with chronic LBP. Only patients classified at baseline assessment as being in the directional preference group (n=140) were included. The effect modifiers tested were: Clear centralization vs directional preference only; Baseline pain location; Baseline pain intensity; and Age. The primary outcomes for this study were pain intensity and disability at the end of treatment (1 month). Treatment effect modification was evaluated by assessing the group versus predictor interaction terms from linear regression models. An interaction ≥ 1.0 for pain and ≥ 3 for disability were considered clinically important. Being older met our criteria for being a potentially important effect modifier; however, the effect occurred in the opposite direction to our hypothesis. Older people had 1.27 points more benefit in pain reduction from MDT (compared to Back School) than younger participants after 1 month of treatment.
This study suggests older age may be an important factor that can be considered as a treatment effect modifier for patients with chronic LBP receiving MDT. As the main trial was not powered for the investigation of subgroups, the results of this secondary analysis have to be interpreted cautiously and replication is required.