Minimal Important Change and Minimal Clinically Important Difference in Pain and Function With Exercise in Hip Osteoarthritis

OBJECTIVE: The objective of this study was to estimate the minimal important change (MIC) and minimal clinically important difference (MCID) for pain and physical function in individuals with hip osteoarthritis (OA) following a physiotherapist-guided exercise intervention. METHODS: Secondary analysis from a randomized controlled trial of 196 adults with hip OA allocated one of two nine-month exercise programs. Patient-reported outcomes measures for hip pain severity (Numeric Rating Scale [NRS], Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] pain subscale) and physical function (WOMAC physical function subscale, Patient-Specific Functional Scale [PSFS]) were collected at baseline and three and nine months. Global ratings of change in pain and physical function at three and nine months served as anchors. RESULTS: MIC estimates were 2.1 and 2.4 points for NRS pain at three and nine months, respectively; 2.8 and 3.0 points for WOMAC pain at three and nine months, respectively; 8.7 and 8.3 points for WOMAC physical function at three and nine months, respectively; and -2.1 and -2.0 points for PSFS at three and nine months, respectively. The MCID estimates were 2.0 and 2.4 points for NRS pain at three and nine months, respectively; 2.8 and 3.0 points for WOMAC pain at three and nine months, respectively; 9.2 and 8.3 points for WOMAC physical function at three and nine months, respectively; and -3.5 and -0.7 points for PSFS at three and nine months, respectively. CONCLUSION: This study provides robust, context-specific MIC and MCID estimates for outcomes in hip OA following exercise. These values can inform the interpretation and design of exercise-based clinical trials for hip OA.