Measuring improvement following total hip and knee arthroplasty using patient-based measures of outcome.
Patient-derived outcome scales have become increasingly important to physicians and clinical researchers for measuring improvement in function after surgery. The goal of the present study was to evaluate the ability of health-status instruments to measure early functional recovery after total hip and total knee arthroplasty. Four hundred and six patients undergoing total hip arthroplasty and 266 patients undergoing total knee arthroplasty completed health-status questionnaires preoperatively and six months postoperatively to determine the standardized response mean. In the second phase of the study, a group of patients undergoing knee and hip arthroplasty were evaluated with several instruments before and after surgery to test for postoperative ceiling effects. The standardized response mean at six months was 1.7 for the MODEMS Hip Core, 1.2 for the MODEMS Knee Core, and 1.5 and 1.1 for the Physical Component Summary of the SF-36 for patients managed with hip and knee replacement, respectively. A standardized response mean of 1.0 is generally satisfactory for measuring improvement in orthopaedic surgery. In Phase 2 of the study, the vast majority of patients who had a score of 95 to 100 (that is, a maximum or near-maximum score) on the joint-specific scales generally believed that the hip or knee was normal and could not be better. The MODEMS, Oxford, and WOMAC scales all demonstrated a ceiling effect following total knee and total hip arthroplasty. These scores likely reflected the patients' perception of the status of the knee or hip rather than an inability to measure their improvement beyond the highest possible score. The Physical Component Summary score of the SF-36 had similar standardized response means when compared with hip and knee-specific instruments, and, therefore, consideration should be given to using this scale without a joint-specific scale for the measurement of improvement following total knee and total hip replacement, as a way to decrease responder burden (that is, the time required to complete the questionnaires).