Minimal and Substantial Improvement Thresholds for Oxford Scores Following Primary Hip and Knee Replacement Based on Patient Satisfaction

BACKGROUND: The mandatory collection of patient-reported outcome measures and the implementation of thresholds for hip and knee replacement surgery represent a growing international trend in value-based health-care policy. Our aim was to investigate whether the Oxford Hip Score (OHS) and Oxford Knee Score (OKS) can be used to accurately predict patient satisfaction, and to estimate thresholds to guide value-based health-care policy. METHODS: All primary total hip replacements (THRs) and total knee replacements (TKRs) for osteoarthritis undertaken at a tertiary academic institution over a 6-year period were identified. Logistic regression models were used to evaluate preoperative and postoperative values for the OHS and OKS, and the change between them, as predictors of patient satisfaction. Optimal thresholds for both the minimal clinically important difference (MCID) and the substantial clinical benefit (SCB) were identified. RESULTS: A total of 1,429 THRs (mean patient age, 66.1 years, standard deviation [SD], 11.1 years; 819 [57.3%] female) and 1,079 TKRs (mean patient age, 68.3 years, SD, 8.4 years; 635 [58.9%] female) were included. For the postoperative OHS, thresholds of 35.5 (95% confidence interval [CI], 29.1 to 41.9) for the MCID and 36.5 (95% CI, 33.0 to 40.0) for the SCB were identified. For the postoperative OKS, thresholds of 30.5 (95% CI, 24.2 to 36.8) for the MCID and 38.5 (95% CI, 36.7 to 40.3) for the SCB were identified. For the change in OHS, thresholds of 19.5 (95% CI, 13.4 to 25.6) for the MCID and 20.5 (95% CI, 16.0 to 25.0) for the SCB were identified. For the change in OKS, thresholds of 13.5 (95% CI, 8.3 to 18.7) for the MCID and 14.5 (95% CI, 11.7 to 17.3) for the SCB were identified. Patients with worse preoperative function had higher thresholds. Preoperative Oxford scores were poor predictors of patient satisfaction. CONCLUSIONS: The thresholds for the postoperative Oxford scores and change scores may guide value-based health-care decision-making using the OHS and OKS. LEVEL OF EVIDENCE: Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.