Quadriceps weakness associates with greater T1ρ relaxation time in the medial femoral articular cartilage 6months following anterior cruciate ligament reconstruction

PurposeQuadriceps weakness following anterior cruciate ligament reconstruction (ACLR) is linked to decreased patient-reported function, altered lower extremity biomechanics and tibiofemoral joint space narrowing. It remains unknown if quadriceps weakness is associated with early deleterious changes to femoral cartilage composition that are suggestive of posttraumatic osteoarthritis development. The purpose of the cross-sectional study was to determine if quadriceps strength was associated with T1 rho relaxation times, a marker of proteoglycan density, of the articular cartilage in the medial and lateral femoral condyles 6months following ACLR. It is hypothesized that individuals with weaker quadriceps would demonstrate lesser proteoglycan density.MethodsTwenty-seven individuals (15 females, 12 males) with a patellar tendon autograft ACLR underwent isometric quadriceps strength assessments in 90 degrees of knee flexion during a 6-month follow-up exam. Magnetic resonance images (MRI) were collected bilaterally and voxel by voxel T1 rho relaxation times were calculated using a five-image sequence and a monoexponential equation. Following image registration, the articular cartilage for the weight-bearing surfaces of the medial and lateral femoral condyles (MFC and LFC) were manually segmented and further sub-sectioned into posterior, central and anterior regions of interest (ROI) based on the corresponding meniscal anatomy viewed in the sagittal plane. Univariate linear regression models were used to determine the association between quadriceps strength and T1 rho relaxation times in the entire weight-bearing MFC and LFC, as well as the ROI in each respective limb.ResultsLesser quadriceps strength was significantly associated with greater T1 rho relaxation times in the entire weight-bearing MFC (R-2=0.14, P=0.05) and the anterior-MFC ROI (R-2=0.22, P=0.02) of the ACLR limb. A post hoc analysis found lesser strength and greater T1 rho relaxation times were significantly associated in a subsection of participants (n=18) without a concomitant medial tibiofemoral compartment meniscal or chondral injury in the entire weight-bearing MFC, as well as anterior-MFC and central-MFC ROI of the ACLR and uninjured limb.ConclusionsThe association between weaker quadriceps and greater T1 rho relaxation times in the MFC suggests deficits in lower extremity muscle strength may be related to cartilage composition as early as 6months following ACLR. Maximizing quadriceps strength in the first 6months following ACLR may be critical for promoting cartilage health early following ACLR.Level of evidencePrognostic level 1.