Measurement Properties of the Thai Version of the Knee Injury and Osteoarthritis Outcome Score and Its Short Forms in Patients With Anterior Cruciate Ligament Injury

INTRODUCTION: The Knee Injury and Osteoarthritis Outcome Score (KOOS) is widely used in anterior cruciate ligament (ACL) research. Although a Thai KOOS exists, its validation was limited to patients with osteoarthritis. Furthermore, Thai KOOS short forms remain unvalidated. Therefore, this study evaluated the validity, reliability, and responsiveness of the Thai KOOS and 3 short forms (KOOS-12, KOOSglobal, and KOOS-ACL) in patients with ACL injury. METHODS: This prospective cohort study involved 95 patients (age range, 18-50 years) scheduled for primary ACL reconstruction. Participants completed the Thai KOOS and International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) at baseline, 2 weeks after baseline, and 3 months postoperatively. Construct validity was assessed via Spearman correlation with the IKDC-SKF. Internal consistency and test-retest reliability were evaluated using Cronbach α and intraclass correlation coefficients, respectively. Responsiveness was quantified via effect size, standardized response mean, and receiver operating characteristic analysis. RESULTS: All KOOS subscales and short forms demonstrated moderate to high correlations with the IKDC-SKF (Spearman correlation coefficients, 0.51-0.87). Internal consistency was excellent (Cronbach α, 0.88-0.93), and test-retest reliability was good (intraclass correlation coefficients, 0.78-0.87). All measures improved significantly at 3 months postoperatively (P < 0.001). Effect sizes (0.63-1.34) and standardized response means (0.66-1.25) were moderate to large. The KOOSglobal and KOOS-12 demonstrated excellent discriminative ability (area under the curve, 0.96 and 0.92, respectively). However, ceiling effects occurred in the Activities of Daily Living (21.1%) and KOOS-ACL Function (20.0%) subscales at 3 months. CONCLUSION: The Thai KOOS and its 3 short forms (KOOS-12, KOOSglobal, and KOOS-ACL) demonstrated good validity, reliability, and responsiveness in patients with ACL injury. LEVEL OF EVIDENCE: II.