Should aggregate scores of the Medical Outcomes Study 36-item Short Form Health Survey be used to assess quality of life in knee and hip osteoarthritis? A national survey in primary care

Abstract

To assess the relevance of using the aggregate physical component score (PCS) and mental component score (MCS) of the Medical Outcomes Study 36-item Short Form Health Survey (SF-36) for patients with knee and hip osteoarthritis (OA). We conducted a cross-sectional national survey in a primary care setting in France. A total of 1474 general practitioners enrolled 4183 patients with hip or knee OA. Construct validity of PCS and MCS was assessed by convergent and divergent validity and factor analysis. Records of 4133 patients (98.8%) were analyzed (2540 knee, 1593 hip OA). PCS mean scores were 32.0+/-8.4 and 31.8+/-8.4 and MCS scores 47.1+/-11.0 and 46.8+/-11.1, for knee and hip OA, respectively. Acceptable convergent and divergent validity was observed, and correlation between PCS and MCS mean scores was low (r=0.14). However, factor analysis performed on the eight subscale scores failed to support the use of PCS and MCS aggregate scores. It extracted two factors which were similar for both OA types and differed from the a priori stratification. Scores for two subscales usually attributed to MCS - emotional role and social functioning - were shared between factors, and scores for another subscale - general health perception - usually belonging to the PCS was in the mental component factor. Our results suggest that aggregate scores from the PCS and MCS of the SF-36 as they are currently defined may not be optimal for used in hip and knee OA patients to assess health-related quality of life.