Quadriceps Morphology 6- to 60-Months After Anterior Cruciate Ligament Tear.

The purpose of this study was to compare quadriceps morphology between legs and individuals with a first-time anterior cruciate ligament (ACL) tear and uninjured controls. This was an exploratory cross-sectional study. We enrolled participants who were aged 19-35 years, and 6-60 months after a first-time ACL tear as well as uninjured controls. Participants attended two sessions separated by a minimum of 7 days. Bilateral knee extensor concentric and eccentric strength and rate of torque development (RTD) were assessed at the first session, and bilateral vastus lateralis muscle biopsies were obtained at the second. Muscle fiber-type specific cross-sectional area (fCSA), fiber-type proportions, and extracellular matrix area were calculated. Between-limb and between-group differences were estimated using mixed-effects regression. 41 of 47 (87%) participants completed the study (n = 21 ACL, n = 20 control). ACL group participants were a median (range) of 23 months from injury, and 78% had undergone an ACL reconstruction. Uninjured group participants had greater knee extensor concentric strength (-39.3 Nm; 95% CI: -54.2, -20.5), eccentric strength (-30.2 Nm; 95% CI: -53.4, -11.6), and RTD (-0.16 Nm/ms; 95% CI: -0.33, -0.04). No between-group or between-limb differences in muscle fiber-type specific fCSA, fiber-type proportions, or extracellular matrix area were observed. Despite deficits in knee extensor muscle performance, no difference in vastus lateralis fiber-type specific CSA, fiber-type proportion, or extracellular matrix area was detected between individuals 6-60 months after an ACL tear and uninjured controls.