Abstract
IMPORTANCE: The minimal clinically important difference (MCID) in a patient-reported outcome measure (PROM) is the smallest change that patients perceive as beneficial. Accurate MCIDs are required when PROMs are used to evaluate the value of surgical interventions. OBJECTIVE: To use well-defined distribution-based and anchor-based methods to calculate MCIDs in the Hip Disability and Osteoarthritis Outcome Score (HOOS) and in the Knee Injury and Osteoarthritis Outcome Score (KOOS) for veterans undergoing primary total hip arthroplasty or total knee arthroplasty. DESIGN, SETTING, AND PARTICIPANTS: A prospective cohort study was conducted of 858 patients undergoing total joint replacement between March 16, 2015, and March 9, 2017, at 3 high-complexity Veterans Affairs Medical Centers. INTERVENTIONS: Patients undergoing total hip arthroplasty or total knee arthroplasty were administered HOOS or KOOS PROMs prior to and 1 year after surgery. The Self-Administered Patient Satisfaction Scale (SAPS) for primary hip or knee arthroplasty was administered at 1-year follow-up as an anchor PROM. MAIN OUTCOMES AND MEASURES: The HOOS and KOOS before and 1 year after surgery, change scores (difference between postoperative and preoperative PROM scores), and MCIDs for each measure. For anchor-based methods, receiver operating characteristic curve analysis was performed, including calculation of the area under the curve. RESULTS: The mean (SD) age of the 271 patients who underwent hip arthroplasty was 65.6 (8.3) years, and the mean (SD) age of the 587 patients who underwent knee arthroplasty was 66.1 (8.2) years. There were 547 men in the knee arthroplasty cohort and 256 men in the hip arthroplasty cohort (total, 803 men). There were significant improvements in the mean values of every PROM, with mean (SD) differences greater than 39 for HOOS Joint Replacement (JR) and every hip subscale (HOOS JR, 39.7 [20.2]; pain, 47.6 [20.5]; symptoms, 45.1 [21.5]; activities of daily living, 43.7 [22.1]; recreation, 49.2 [33.5]; quality of life, 50.3 [27.8]) and mean (SD) differences greater than 29 for KOOS JR and every knee subscale (KOOS JR, 30.4 [17.5]; pain, 38.0 [20.4]; symptoms, 29.5 [22.1]; activities of daily living, 34.8 [20.5]; recreation, 34.6 [31.1]; quality of life, 35.2 [26.8]). Different calculation methods yielded a wide range of MCIDs. Distribution-based approaches tended to give lower values than the anchor-based approaches, which gave similar values for most PROMs. Area under the curve values demonstrated good to excellent discrimination for SAPS for nearly all PROMs. CONCLUSIONS AND RELEVANCE: Minimal clinically important difference estimates can be highly variable depending on the method used. Patient satisfaction measured by SAPS is a suitable anchor for the HOOS and KOOS. This study suggests that the SAPS-anchored MCID values presented here be used in future studies of total hip arthroplasty and total knee arthroplasty for veterans.