Not All Muscles Recover Equally: Longitudinal Mri Evaluation Of Quadriceps Muscle Atrophy And Recovery After Anterior Cruciate Ligament Reconstruction

PURPOSE: Quadriceps weakness after anterior cruciate ligament reconstruction (ACLR) have been well documented; however, whether the degree of atrophy varies among the 4 quadriceps muscles and how restoration of muscle size contributes to strength recovery post-ACLR remains unknown. This study examined the differences in atrophy among the 4 quadriceps muscles through MRI and assessed the relationship between muscle hypertrophy and strength recovery over time post-ACLR. METHODS: Thirteen subjects with unilateral ACLR were examined at 6 months and 1 year post-ACLR. Axial MRI was obtained to calculate the volume for each of the 4 quadriceps muscles in each leg: vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), and rectus femoris (RF). Isokinetic (60°/s) strength of the quadriceps muscle group was also assessed. The degree of atrophy and strength deficit was calculated as the % difference of the uninjured leg. A two-way ANOVA with repeated measures was used to compare the differences in atrophy among the 4 muscles across the 2 time points. Pearson correlations were used to assess the relationship between changes in muscle volume and strength of the ACLR legs over the 2 time points. RESULTS: The results of the 2-way ANOVA for the degrees of atrophy indicated a significant main effect for time and muscle (p < 0.001) without a significant muscle-by-time interaction (p = 0.053). For the time effect, subjects exhibited significantly greater atrophy across all muscles at 6 months (22.4 ± 7.2%, 17.3 ± 6.7%, 24.3 ± 6.0%, and 13.4 ± 9.6% atrophy for VL, VI, VM, and RF) compared to the atrophy at 1 year post-ACLR (16.4 ± 6.1%, 13.4 ± 10.0%, 17.7 ± 9.2, and 11.4 ± 9.7% for VL, VI, VM, and RF). The VL and VM had a significantly greater atrophy than the VI (p ≤ 0.045) and RF (p ≤ 0.002). The recovery of quadriceps strength from 6 months to 1 year (by 22.9 ± 24.1%) was not significantly correlated with the recovery of quadriceps volume (by 3.8 ± 8.3%) in the ACLR legs (r = 0.50, p = 0.09). CONCLUSIONS: Persistent quadriceps weakness was found 1-year post-ACLR with greater atrophy in the VL/VM than VI/RF. Limited and heterogeneous hypertrophy over time and the lack of significant association between hypertrophy and strength indicates a need of post-ACLR rehabilitation to facilitate uniform morphological changes across all quadriceps muscles. Supported by: This study was in part supported by the research grants from the Georgia Foundation for Physical Therapy (GFPT).