Reliability and validity of the Japanese Orthopaedic Association hip score

The Japanese Orthopaedic Association (JOA) hip score has been widely used in Japan as a method to assess hip joint diseases. The JOA hip score consists of four subcategories: pain (Pain), range of motion (ROM), ability to walk (Gait), and activities of daily life (ADL). We present the first report to verify the reliability and validity of the JOA hip score. A total of 123 patients with osteoarthritis of a unilateral hip and 29 patients with osteonecrosis of a unilateral hip were investigated. The JOA hip score was recorded by orthopedic surgeons in their offices. On the same day, each patient answered a Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) (Japanese version 1.2) by himself or herself. The SF-36 survey measures eight subscales. The internal-consistency reliability of the JOA hip score was evaluated by Cronbach's coefficient alpha. The validity of the JOA hip score was tested by Spearman's correlation coefficients between the four subcategories of the JOA hip score and the eight SF-36 subscales. When patients with osteoarthritis with conservative treatment were assessed by the JOA hip score, Cronbach's coefficient alpha was 0.70, demonstrating internal-consistency reliability. However, when the JOA hip score was used for other groups, Cronbach's coefficient alpha was < 0.70, demonstrating the lack of internal-consistency reliability. Significant correlations were observed between Pain and bodily pain (r = 0.63), between Gait and physical functioning (PF) (r = 0.70), and between ADL and PF (r = 0.81), but not in any other combinations. We found that the JOA hip score is a reliable system only for patients with osteoarthritis of the hip with conservative treatment. The JOA hip score is a scaling system with convergent and discriminant validity for the assessment of physical function and pain.