A Comparison of Methods for Tracking Muscle Quality During Early-Phase Rehabilitation Following Anterior Cruciate Ligament Reconstruction

Background: Echo intensity (EI) has emerged as a promising and accessible tool for tracking changes in skeletal muscle quality; however, its utility during early-phase rehabilitation has not been studied. Using an observational cohort design, we examined changes in quadriceps muscle strength, size, and quality, along with self-reported knee function, 2, 6, and/or 10 weeks following anterior cruciate ligament reconstruction (ACLR). Methods: Thirteen participants (4 males, 9 females; mean age = 23 years) were assessed for bilateral isometric peak torque and cross-sectional area (CSA) and corrected EI of the vastus lateralis and rectus femoris. Self-reported knee function was measured using the International Knee Documentation Committee (IKDC) questionnaire. Results: Quadriceps peak torque was significantly lower in the surgical limb at 2 weeks following surgery but increased from weeks 2 to 10, while the nonsurgical limb remained stable. IKDC scores improved significantly over time. Vastus lateralis CSA decreased in the surgical limb between weeks 2 and 6, while rectus femoris CSA increased between weeks 6 and 10 in both limbs. Corrected EI values did not change over time. No significant correlations were observed among changes in muscle strength, size, quality, or self-reported knee function. Conclusions: We conclude that quadriceps strength, size, quality, and self-reported knee function change independently and do not follow a shared recovery trajectory.