Longitudinal Assessment of Quadriceps Muscle Morphology Before and After Anterior Cruciate Ligament Reconstruction and Its Associations With Patient-Reported Outcomes

Background: Reductions in muscle size are common after anterior cruciate ligament reconstruction (ACLR) and may contribute to suboptimal patient outcomes. However, few studies have quantified postoperative alterations in muscle quality and evaluated its associations with patient-reported function. Hypotheses: Rectus femoris cross-sectional area (CSA) will decrease postoperatively but improve at return to activity (RTA), rectus femoris muscle quality (percentage fat [PF]) will increase postoperatively and be greater at RTA compared with preoperative values, and rectus femoris CSA and PF will be associated with International Knee Documentation Committee (IKDC) scores at both postoperative time points. Study Design: Case series. Methods: A total of 26 individuals who sustained an ACL injury and underwent reconstructive surgery were evaluated preoperatively (T-0), 9 weeks post-ACLR (T-1), and at RTA. Rectus femoris CSA and PF were evaluated bilaterally via ultrasound imaging, and patient-reported function was assessed using the IKDC score. Results: Bilateral reductions in rectus femoris CSA were noted from T-0 to T-1 (P < 0.01). Only the uninvolved limb returned to preoperative CSA (P = 0.80), as the involved limb failed to return to preoperative levels at RTA (P = 0.04). No significant changes in rectus femoris PF were observed across time points (P > 0.05). Lesser PF (P < 0.01) but not CSA (P = 0.75) was associated with higher IKDC score at T-1. Lesser PF (P = 0.04) and greater CSA (P = 0.05) was associated with higher IKDC score at RTA. Conclusion: Substantial atrophy occurs bilaterally after ACLR, and the involved limb does not return to preoperative muscle size despite the patient completing rehabilitation. Quadriceps muscle morphology is associated with patient-reported function and may be an important rehabilitation target after ACLR.