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

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.

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.

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, ICC_2,1 (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.

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.