Psychometric properties of the EQ-5D-5L in patients with hip or knee osteoarthritis: reliability, validity and responsiveness.

PURPOSE: To study the psychometric properties, including reliability, validity and responsiveness, of the Spanish EQ-5D-5L questionnaire for patients with hip or knee osteoarthritis (OA).

METHODS: We included 758 patients with hip or knee OA who completed the EQ-5D-5L and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at baseline, of whom 644 also did 6 months later. The EQ-5D-5L contains five questions from which a utility index is derived. The WOMAC covers three dimensions: pain, stiffness and physical function. Floor and ceiling effects were calculated. Reliability was assessed using Cronbach's alpha. Convergent validity was tested using the Spearman correlation coefficient between EQ-5D-5L and WOMAC. We examined known-groups validity by comparing the EQ-5D-5L between subgroups defined by WOMAC scores using ANOVA or the Kruskal-Wallis test. Effect sizes were calculated to assess responsiveness, and minimal clinically important difference (MCID) was estimated.

RESULTS: The EQ-5D-5L showed minimal floor and ceiling effects (< 3%). Cronbach's alpha was 0.86. The EQ-5D-5L index was strongly correlated with WOMAC pain and function scores (- 0.688 and - 0.782). Patients with higher WOMAC scores had significantly (p < 0.0001) lower EQ-5D-5L index. The 20.19% had hip or knee replacement during the follow-up. Effect sizes were small among non-surgical patients, but > 0.80 among "improved" surgical patients, being the MCID for improvement 0.32 points.

CONCLUSIONS: The results support the reliability, validity and responsiveness of the EQ-5D-5L, overcoming the limitations of the EQ-5D-3L in these patients. Therefore, the EQ-5D-5L could be very useful as an outcome measure, at least in patients with hip or knee OA.