Validation and defining the minimal clinically important difference of the Japanese version of the IKDC Subjective Knee Form.

<bold>Background: </bold>This study aimed to validate and determine the minimal clinically important difference (MCID) in the Japanese version of the International Knee Documentation Committee Subjective Knee Form (Japanese IKDC-SKF) for patients with anterior cruciate ligament (ACL) injuries.<bold>Methods: </bold>This prospective study was performed using the COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN) guideline to assess the measurement properties of reliability, responsiveness, validity, and interpretability of the Japanese IKDC-SKF.<bold>Results: </bold>A total of 152 patients were enrolled in the study. The Japanese IKDC-SKF had excellent internal consistency [Cronbach's alpha (95% confidence interval, CI) was 0.90 (0.88-0.92), and the test-retest reliability [intraclass correlation coefficient, ICC2,1 (95% CI)] was 0.97 (0.94-0.98). The content validity (r), which was interpretable between the Japanese IKDC-SKF and the Japanese Anterior Cruciate Ligament questionnaire 25 was -0.87 (P < 0.001). The construct validity for the IKDC-SKF was 86% (six of seven hypotheses were consistent with the results), also indicating high validity. Responsiveness of the Japanese IKDC-SKF was confirmed, with an acceptable area under the curve of 0.81 and a large effect size (Cohen's d of 0.8). There were no floor or ceiling effects. The MCID for the Japanese IKDC-SKF for ACL injury was 10.7.<bold>Conclusions: </bold>Our results indicate that the Japanese version of the IKDC-SKF is a reliable, valid, and responsive measurement instrument with which to evaluate the physical function of patients with ACL injuries. [ABSTRACT FROM AUTHOR]