Knee Extensor Strength is Associated with Femoral Cartilage Thickness in Individuals with ACL Reconstruction

Abstract

PURPOSE: To (1) determine the relationship between quadriceps function and femoral cartilage morphology in individuals with anterior cruciate ligament reconstruction (ACLR), and (2) compare quadriceps function and femoral cartilage morphology between injured and uninjured limbs. METHODS: Quadriceps function and femoral cartilage was assessed with unilateral ACLR in 20 subjects (women=15, age= 22.3±3.3years, time since ACLR=44.9±32.8 months). Quadriceps function was assessed using peak isometric knee extension torque (PT) and rate of torque development (RTD) at 45 degrees of knee flexion, and peak isokinetic knee extensor torque at 60, 180 and 240°/sec. Femoral cartilage morphology (area and thickness) were obtained via ultrasound imaging at 140° of knee flexion. Partial correlations were used to evaluate the associations between indices of quadriceps function, and cartilage area and thickness accounting for time since reconstruction. Paired samples t-test were used to evaluate interlimb differences. RESULTS: The ACLR limb produced smaller isometric peak torque (2.56±0.42 vs. 2.75±0.30 Nm/kg, p=0.04), slower isometric rate of torque development (38.12±13.27 vs. 47.81±17.99 Nm/sec/kg, p=0.03), and isokinetic peak knee extensor torque at 60°/sec (2.38±0.54 vs. 2.80±0.63 Nm/kg, p≤0.01) compared to the uninjured limb. No differences were found in isokinetic peak torque at 180 or 240°/sec (p=0.06 and 0.60, respectively). After accounting for time since ACLR, a positive association was found between isometric peak torque and medial femoral cartilage thickness (r=0.41, p=0.04). CONCLUSIONS: The ACLR limb demonstrated deficits in quadriceps function. We found a moderate association between isometric peak torque and medial femoral cartilage thickness. Our results suggest that restoring quadriceps strength may delay femoral cartilage thinning following ACLR.