Objective：We aimed to examine the criterion-related validity of observable items of gait abnormality in patients with knee osteoarthritis (OA) using three-dimensional gait analysis and to assess the test-retest reliability.

Methods：The items of gait abnormality were pooled from a prior study and rated using a 3-point scale. Content validity was examined by four experts in knee OA research and accepted when there was an agreement among at least three experts. Correlation between abnormality rating and three-dimensional gait analysis data was examined. The test-retest reliability of the agreement rate was then assessed in the same subject twice.

Results：Eleven items were pooled, and all met the criterion of content validity. Eight items showed adequate correlation with the three-dimensional gait analysis data and had test-retest reliability exceeding 0.61.

Conclusion：In patients with knee OA, observable items of gait abnormality had good test-retest reliability and criterion-related validity according to the three-dimensional gait analysis data.