Rectus femoris and vastus intermedius muscle asymmetries following ACL reconstruction.

Abstract

Anterior cruciate ligament reconstruction (ACLR) induces deleterious neuromuscular alterations. Musculoskeletal ultrasonography provides an accessible method to quantify muscle size and quality in patients with ACLR who suffer from persistent skeletal muscle atrophy. This study compares rectus femoris and vastus intermedius muscle thickness and echo intensity using extended field-of-view ultrasonography in individuals with a history of ACLR versus non-injured controls. Twenty-six individuals with previous ACLR and twenty controls participated. Extended field-of-view ultrasonography was used to analyze muscle thickness at proximal, middle, and distal regions of the thigh, while echo intensity was measured to assess muscle quality. Findings indicate significant asymmetries in muscle thickness (p < 0.01, ηp2 = 0.312) and echo intensity (p = 0.024, ηp2 = 0.111) for the ACLR group, favoring the uninvolved leg, with no site-specific differences between groups. Results show muscle-specific size differences, with greater vastus intermedius than rectus femoris muscle thickness in controls (p < 0.01, d = 0.609), but no difference between muscles in either leg of the ACLR group (p > 0.05, d = 0.094). Overall, these results highlight unique skeletal muscle changes between the biarticular rectus femoris and monoarticular vastus intermedius following ACLR, likely reflecting postoperative deficiencies in knee extension function.