MRI-Based Volumetric Analysis of the Quadriceps Muscles Correlation With Knee Extension Strength in Patients Undergoing Anterior Cruciate Ligament Reconstruction

Background: Preoperative quadriceps and hamstring muscle weakness may predispose patients to strength deficits and prolonged recovery in the setting of anterior cruciate ligament (ACL) injury. Three-dimensional (3D) magnetic resonance imaging (MRI) analysis has been developed to provide a comprehensive assessment of the thigh musculature. Purpose: To (1) describe the magnitude of quadriceps and hamstring muscle weakness relative to the uninjured limb preoperatively in patients with known ACL tears, and (2) determine if preoperative quadriceps and hamstring muscle volume correlate with quadriceps knee extension strength and hamstring knee flexion strength. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Patients undergoing primary ACL reconstruction (ACLR) underwent MRI scans of the bilateral lower extremities and strength testing preoperatively within 7 days of ACLR. Three-dimensional MRI–based autosegmentation was used to measure the volume of individual quadriceps and hamstring muscles. Preoperative knee extension and flexion strength were assessed isometrically at 90° and isokinetically. Linear mixed-effects models were used to assess muscle volume by limb interaction effect on strength. Pearson correlation coefficients ( r ) were used to assess the association between muscle volume and strength in the injured and uninjured limbs. Results: In total, 72 patients were included (mean age, 26.6 ± 8.8 years; 64% male) with the median time to preoperative strength assessment and MRI within 90 days of injury. Comparing the ACL-injured limb to the uninjured limb, isometric knee extension and flexion strength demonstrated mean limb symmetry indices (LSIs) of 80.1% ± 18.5% ( P < .001) and 83.7% ± 17.7% ( P < .001), respectively. Additionally, measured quadriceps and hamstring volume demonstrated mean LSIs of 89.9% ± 8.8% ( P < .001) and 95.4% ± 4.6% ( P < .001), respectively. There was moderate to strong positive associations between individual muscle volume and strength in both the injured and uninjured limbs, regardless of the mode of strength assessment ( r = 0.43-0.84; all P < .001). Conclusion: Preoperatively, a 20% deficit in isometric knee extension strength and a 10% deficit in quadriceps muscle volume was noted in the ACL-injured knee compared to the uninjured limb. A moderate to strong correlation between quadriceps strength and each individual quadriceps muscle volume measured by a 3D MRI platform was observed before ACLR. Findings suggest the utility of automated 3D MRI volumetric segmentation as an adjunct to complement formal preoperative strength assessment. Additionally, this method may be used to identify patients at risk for delayed and/or degraded functional outcomes after ACLR.