Responsiveness and Minimal Clinically Important Difference of the Thai Version of the International Knee Documentation Committee Subjective Knee Form in Patients With Anterior Cruciate Ligament Injury

BACKGROUND: The International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) is a knee-specific patient-reported outcome (PRO) measure that is commonly used to evaluate patients with various knee disorders. The Thai version of the IKDC-SKF (Thai IKDC-SKF) was shown to have good validity and reliability; nonetheless, no data regarding its responsiveness are available. PURPOSE: To evaluate the responsiveness of the Thai IKDC-SKF for assessing patients with anterior cruciate ligament (ACL) injury and determine the minimal clinically important difference (MCID) for this PRO measure. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: This prospective study included ACL-injured patients who were scheduled for ACL reconstruction (ACLR) at a single institution. The patients completed the Thai IKDC-SKF at the baseline and the 6-month postoperative follow-up. The global rating of change scale was an anchor question that evaluated patients’ overall perception of a clinical change compared with their preoperative condition. The effect size and standardized response mean were calculated. The MCID was identified with an anchor-based approach by plotting a receiver operating characteristic curve and calculating the value that maximized the Youden index. RESULTS: Of 59 enrolled patients, 53 patients (89.8%) completed the preoperative and 6-month postoperative Thai IKDC-SKF. The mean (±SD) age of the participants was 32.3 ± 10.3 years, and 86.8% were men. The mean Thai IKDC-SKF score improved significantly from preoperatively to the 6-month follow-up (from 56.3 ± 14.9 to 70.8 ± 14.1, respectively; P < .001), with an effect size of 0.975 and a standardized response mean of 0.977. A receiver operating characteristic curve was generated to determine the ability of the Thai IKDC-SKF to distinguish between improved patients and unimproved patients, and the area under the curve was 0.80 (95% CI, 0.68-0.92), which was considered excellent. The MCID was 15.5, which yielded a sensitivity and specificity of 0.55 and 1, respectively. CONCLUSION: This study confirmed the responsiveness of the Thai IKDC-SKF for detecting a clinical change in ACL-injured patients after ACLR. The identified MCID of 15.5 can be used to calculate the significant clinical change and sample size in future studies.