Relationship between Muscle Cross-Sectional Area, Thigh Circumference and International Knee Documentation Committee after Anterior Cruciate Ligament Reconstruction

Introduction: While the International Knee Documentation Committee (IKDC) score is widely used in rehabilitation after Anterior cruciate ligament (ACL) reconstruction, its subjectivity may not fully capture physiological recovery. Evidence directly linking objective measures such as muscle cross-sectional area (CSA) and thigh circumference with IKDC outcomes remains limited, which this study seeks to address. Objective: To investigate whether thigh muscle CSA and thigh circumference are correlated with IKDC scores after ACL reconstruction, and whether these objective muscle indices can reflect or predict functional scores. Methods: Nineteen patients (13 males, 6 females; mean age 27.1 ± 7.9 years; height 177.1 ± 10.0 cm; weight 75.3 ± 16.1 kg; BMI 23.8 ± 3.5) were evaluated for vastus medialis (VM), semitendinosus (ST), and biceps femoris (BF) CSA and thigh circumference at baseline, week 3, and week 6 post-ACL reconstruction. IKDC scores were recorded concurrently and at week 12, 15, 18, and 24 after the first 6 weeks as follow-ups. Results: greater VM CSA at week 6 was moderately correlated with higher IKDC scores at week 18. BF CSA at baseline and week 6 demonstrated weak positive correlations with week 24 IKDC, whereas ST CSA at week 6 showed a weak negative correlation. Thigh circumference showed a weak negative correlation at week 15. Conclusions: VM and BF CSA provided limited but significant predictive value for functional recovery, while thigh circumference alone was unreliable. These findings highlight the clinical importance of integrating objective morphological and neuromuscular assessments to guide rehabilitation and optimize return-to-sport decisions.