Associations Between Muscle Morphology Measured with Ultrasonography and Self-Reported Function Following Anterior Cruciate Ligament Reconstruction

Abstract

Deficits in quadriceps function are common in patients who sustain an anterior cruciate ligament (ACL) injury and undergo subsequent ACL reconstruction (ACLR). Quadriceps atrophy is among the notable changes in muscle tissue after ACLR. The relationship between muscle morphology and self-reported function should be established so treatment options can be targeted to improve function after ACLR. PURPOSE: (1) To evaluate rectus femoris (RF) cross-sectional area (CSA) and intramuscular fat percent (PF) in the injured and uninjured limb from 9 weeks post ACLR to return to activity (RTA) and (2) identify associations between injured limb quadriceps CSA, PF and self-reported function. METHODS: 28 individuals with primary unilateral ACLR (Age=16.6±2.7; Weight=71.8±17.7; 64% female; 18 bone-patellar tendon-bone; 2 quadriceps tendon; 5 hamstring tendon) were recruited for this study. RF was imaged at 15cm proximal of superior border of the patella. Quadriceps CSA and PF of the injured and uninjured limb were used for analysis. Self-reported function was evaluated using the International Knee Documentation Committee score (IKDC). Paired-samples t-tests were used to compare inter-limb differences in CSA and PF and changes from 9 weeks to RTA. Partial correlations adjusting for sex were used to analyze the relationship between RF morphology and IKDC scores. RESULTS: Injured limbs had smaller RF CSA at each time point (4.5±1.6cm2 vs 5.2±1.9cm2, p<.01 and 5.2±1.9cm2 vs 5.6±2.1 cm2, respectively) compared to the uninjured limb. Injured limb CSA increased at RTA (4.5±1.6cm2 vs 5.2±1.9cm2, p<.01) while the uninjured limb did not (p=0.12). No differences in PF were found between limbs (p=0.18, and p=0.43, respectively) or time point (p=0.67, and p=0.92, respectively). After adjusting for sex, larger injured limb CSA was associated with higher IKDC scores at 9 weeks and trended toward significance at RTA (r=0.32, p=0.05, and r=0.26, p=0.09, respectively). Injured limb PF was negatively associated with IKDC scores at both time points (r=-0.55, p=<.01, and r=-0.39, p=0.02, respectively). CONCLUSIONS: Inter-limb differences in RF muscle CSA are not ameliorated at RTA. RF CSA and PF are associated with self-reported function in individuals with ACLR and should be treatment targets to improve patient function following injury.