Background: A variety of outcome measures are available to evaluate physical impairment and disability in patients with knee osteoarthritis, and most physician-rated measures are not validated. The objective of this study was to assess the validity and reliability of an observer-based knee scoring system of the Japanese Orthopaedic Association (the JOA) commonly used in Japanese clinical practice, and to determine demographic variables affecting the score.
Methods: A consecutive series of 85 patients with primary knee osteoarthritis completed the JOA (four domains pain on walking, pain on ascending or descending stairs, range of motion, and joint effusion), two validated patient-rated measures including the generic instrument of the Medical Outcomes Study 36-Item Short-Form (the SF-36) Health Survey, and the disease-specific scale of the Japanese Knee Osteoarthritis Measure (the JKOM), and a performance based timed-up-and-go test (TUG). Concurrent validity was determined by examining correlations of the JOA with the SF-36 and the JKOM. Construct validity was verified by correlating each domain of the JOA with objective measurements of TUG using Spearman's rank correlation coefficient. Intra- and interobserver reliability and internal consistency of the JOA were evaluated with another cohort of 32 patients who had a knee disorder at baseline and again at a mean of 18 days later.
Results: The JOA was significantly correlated with validated patient-rated outcome measures (the JKOM, the SF-36), indicating concurrent validity of the JOA. Domains of the JOA had significant correlations with the TUG, showing adequate construct validity. Intra- and interobserver reliability for the JOA showed a moderate to almost perfect agreement, and internal consistency of Cronbach's α indicated that the JOA score was a highly reliable instrument to assess knee osteoarthritis. As a demographic variable, age was highly correlated with the JOA.
Conclusions: The JOA, generally used as an observer-derived knee scoring system, is a valid and reliable tool for evaluating functional status in patients with knee osteoarthritis.