RELATIONSHIP BETWEEN QUADRICEPS MUSCLE THICKNESS, MUSCLE STRENGTH, KNEE FUNCTION, AND QUALITY OF LIFE FOLLOWING GRADED BACKWARD TREADMILL TRAINING AFTER ACL RECONSTRUCTION

Abstract

Background: Recovery after anterior cruciate ligament reconstruction (ACLR) is multidimensional. Quadriceps muscle atrophy and weakness may coexist with impaired knee function and reduced quality of life. Although graded backward treadmill training improves these outcomes, the relationships among structural muscle recovery, strength recovery, knee function, and ACL-specific quality of life require separate evaluation. Objective: To determine the relationships between changes in quadriceps muscle thickness, quadriceps muscle strength, knee function, and quality of life following graded backward treadmill training after ACL reconstruction. Methods: A secondary analysis was performed using participant-level data from 60 individuals, 3–6 months after unilateral arthroscopic ACL reconstruction with semitendinosus graft. Participants had been randomized into five groups (n=12 each): backward treadmill walking at 0°, 5°, 10°, or 15° inclination, or conventional rehabilitation. Training was delivered for 20 minutes per session, three sessions per week for four weeks. Quadriceps strength was assessed using a MicroFET handheld dynamometer, muscle thickness using musculoskeletal ultrasound, knee function using the International Knee Documentation Committee (IKDC) subjective knee form, and quality of life using the ACL-QOL questionnaire. Change scores were calculated as post-intervention minus baseline values. Because several change-score distributions were non-normal, Spearman rank correlations were used; 95% confidence intervals were estimated by bootstrap resampling. Results: All groups improved across the four outcome domains. The 15° group showed the largest mean changes in strength (0.86±0.28), muscle thickness (0.64±0.64 cm), IKDC (31.88±12.17), and ACL-QOL (26.38±21.21). Across all 60 participants, increase in muscle thickness was weakly associated with strength gain (ρ=0.266, p=0.040). Strength gain was positively associated with IKDC improvement (ρ=0.332, p=0.010), and IKDC improvement was positively associated with ACL-QOL improvement (ρ=0.357, p=0.005). Muscle-thickness change was not significantly associated with IKDC or ACL-QOL change, and strength change was not significantly associated with ACL-QOL change. In exploratory regression adjusted for intervention group, strength and muscle-thickness changes were not independent predictors of IKDC change; IKDC change remained independently associated with ACL-QOL change (B=0.70, 95% CI 0.27–1.13, p=0.001). Conclusion: Following ACL reconstruction, structural, strength, functional, and quality-of-life recovery appear related but are not interchangeable. Greater quadriceps strength recovery was associated with better knee-function improvement, while improvement in knee function showed the clearest relationship with improvement in ACL-specific quality of life. Multidimensional assessment using ultrasound, dynamometry, IKDC, and ACL-QOL may provide a more complete picture of rehabilitation progress.