Outcomes after total hip replacement based on patients' baseline status: what results can be expected?

OBJECTIVE: We evaluated patient satisfaction with total hip replacement (THR) to establish cut points of sufficient improvement based on the patient acceptable symptom state (PASS) and receiver operating characteristic (ROC) curves, and compared them with measures derived from the minimum clinically important difference (MCID), taking into account patients' baseline status.
METHODS: Two cohorts of prospectively recruited patients on waiting lists for THR were studied. Sociodemographic data and comorbidities were recorded. Patients completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and other patient-reported outcomes questionnaires before THR and 6 months afterward. Cut points of sufficient improvement were established by the PASS, ROC, and MCID and were compared.
RESULTS: Patients satisfied with THR had, by preintervention WOMAC tertiles, gains of 19.4, 34.1, and 49.3 in the WOMAC pain domain and 17.8, 30.8, and 41.4 in the WOMAC functional limitation domain. The PASS cut points determined were 20, 25, and 25 for postintervention WOMAC pain and 28, 35, and 42 for functional limitation. ROC cut points were 19, 25, and 25 for postintervention pain and 26.4, 39, and 40 for functional limitation. Agreement among cut points classifying patients as responders to THR was 1.0 for pain with both PASS and ROC, and 0.85 for functional limitation; 0.6 for pain between MCID and PASS or ROC, and 0.58 and 0.60 for functional limitation.
CONCLUSION: Cut points of expected gain after THR can help clinicians, researchers, and managers to identify suitable candidates for THR, although such measures must be used with caution.