With the high incidence of knee osteoarthritis (OA) in Japan, there is a strong need not only for surgical therapies, but also for validated outcome measures. For this study, we completed cross-cultural adaptation, testing and validation of the Oxford knee score (OKS) for prospective use in national and international clinical studies involving Japanese patients.
The Japanese version of the OKS was developed according to the standard cross-cultural adaptation guidelines. For validation, the OKS was tested on 54 patients diagnosed with OA, osteonecrosis, ligament or meniscus injury. Reliability was tested using the intraclass correlation coefficient (ICC). Internal consistency or homogeneity was assessed using Cronbach's alpha. The correlation between the Japanese OKS, WOMAC and SF-36 questionnaires was used to assess construct validity.
No major difficulties were encountered with the translation and pre-testing stages. For reliability and validity, the Japanese OKS was completed without any missed responses by 53 (98.15%) and 52 (96.30%) patients at the first and second distribution, respectively. The total OKS showed good reliability with an ICC of 0.85. Internal consistency was strong (Cronbach's alpha = 0.90). Strong construct validity (ICC values of 0.51-0.84) was obtained against the WOMAC and SF-36 (physical functioning, role-physical, bodily pain, and social functioning subscales) scores. Notable "ceiling" effects of the OKS were reported for 11 of the 12 questionnaire items.
The Japanese OKS has proven to be a reliable and valid instrument for the self-assessment of knee pain and function in Japanese speaking patients with knee OA and other knee complaints.