An outcome measure for Japanese people with knee osteoarthritis

OBJECTIVE: We describe a new outcome measure for Japanese patients with knee osteoarthritis, the Japanese Knee Osteoarthritis Measure (JKOM). METHODS: The outcome measure was designed to incorporate the concepts of the World Health Organization's International Classification of Functioning, Disability and Health 2001, and to reflect the specific Japanese cultural lifestyle, which differs from Western countries. To examine the validity and reliability of this measure and to determine the underlying set of measures, psychometric measurements including factor analysis were conducted in comparison with 2 other health related scales, the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). The following psychometric properties were tested with this new measure: test and retest reliability, internal consistency, content validity, construct validity, and criterion related validity. RESULTS: The measure was proved to have sufficient reliability and validity by means of statistical evaluation and comparison with other health related scales. Three domains are clearly separated on the loading pattern by factor analysis: pain, limitation in mobility related to daily activity, and restriction of participation in social life and health perception. CONCLUSION: The JKOM, a new knee OA measure, has sufficient reliability and validity for studies of the clinical outcomes of Japanese people with knee OA.