Quantifying Muscle Volume Deficits Among 38 Lower Extremity Muscles in Collegiate Football Athletes After Anterior Cruciate Ligament Reconstruction

Background: Quadriceps dysfunction is ubiquitous after anterior cruciate ligament (ACL) reconstruction (ACLR). Addressing quadriceps dysfunction is crucial to improve function, reduce the reinjury risk, and maintain long-term knee health. While deficits specific to the quadriceps are well documented, less is known about the effect of an ACL injury on other lower extremity muscle groups. Purpose/Hypothesis: The purpose of this exploratory analysis was to quantify and rank lower extremity muscle volume deficits using magnetic resonance imaging in collegiate football athletes after ACLR. It was hypothesized that the quadriceps muscles would present with the greatest deficits and that compensatory hypertrophy of muscles at adjacent joints such as the hip and ankle would be observed. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study is a secondary analysis from an ongoing multicenter prospective cohort study involving Division I collegiate football athletes. Athletes who underwent primary unilateral ACLR (1 [3%] allograft, 2 [7%] quadriceps tendon autograft, 22 [73%] bone–patellar tendon–bone autograft, 5 [17%] hamstring tendon autograft) and magnetic resonance imaging were included. Muscle volumes (mL·kg –1 ·m –1 ) were quantified bilaterally from 38 lower extremity muscles using machine learning technology. Paired-samples t tests were performed between limbs for each muscle, which were then ranked and visualized in a forest plot based on standardized mean differences (surgical – nonsurgical limb). Results: A total of 30 athletes (mean time from surgery, 27.9 ± 19.0 months) were included. The largest muscle volume deficits in the surgical limb were seen in the 3 uniarticular quadriceps muscles, followed by the biarticular triceps surae muscles. The rectus femoris and soleus did not show significant differences between limbs. Conversely, the fibularis muscle group had a greater muscle volume in the surgical limb compared with the nonsurgical limb. Most other muscle groups did not present significant differences between limbs. Conclusion: Persistent quadriceps atrophy in a cohort of high-level athletes over 2 years after ACLR was highlighted in this study. Deficits in the gastrocnemius muscles, but not in the soleus, were also identified. This comprehensive approach examining various lower extremity muscles revealed latent muscle volume deficits present after ACLR.