Evidence-based hierarchy of pain outcome measures for osteoarthritis clinical trials and meta-analyses.

Objective: To rank commonly used patient-reported outcome measures (PROMs) for assessing pain in osteoarthritis trials according to their assay sensitivity, defined as the ability of a PROM to distinguish an effective from a less effective intervention or placebo, proposing a hierarchy for PROM selection in trials and data-extraction in meta-analyses.

Design: Analysis of trials with placebo, sham, or non-intervention control that included ≥100 patients per arm with knee/hip osteoarthritis, reporting treatment effects on ≥2 pain PROMs. Treatment effects from all PROMs were standardized on a 0-100 scale. Negative mean differences indicated a larger effect of the experimental treatment compared to control. We ranked PROMs by assay sensitivity using a Bayesian multi-outcome synthesis random-effects model.

Results: 135 trials comprising 57,141 participants were included. The ranking of PROMs from highest to lowest assay sensitivity was as follows: pain overall, pain on stairs, pain at night, pain on walking, pain at rest, WOMAC pain, WOMAC global, Lequesne index. Pain overall, the highest-ranked PROM, had a pooled mean difference of -6.96 (95%CrI -7.94, -6.02), while WOMAC pain, the most reported PROM in our study, had a pooled mean difference of -4.90 (95%CrI -5.55, -4.26). The pooled ratio of mean differences between pain overall and WOMAC pain was 1.42 (95%CrI 1.30, 1.55), representing a 42% larger effect size with pain overall.

Conclusions: Pain overall has better assay sensitivity than other pain PROMs. Investigators should consider the hierarchy proposed in this study to guide PROM selection in osteoarthritis clinical trials and data extraction in osteoarthritis meta-analyses.