Persistent Biomechanical Alterations After ACL Reconstruction Are Associated With Early Cartilage Matrix Changes Detected by Quantitative MR

BACKGROUND: The effectiveness of anterior cruciate ligament (ACL) reconstruction in preventing early osteoarthritis is debated. Restoring the original biomechanics may potentially prevent degeneration, but apparent pathomechanisms have yet to be described. Newer quantitative magnetic resonance (qMR) imaging techniques, specifically T(1ρ) and T(2), offer novel, noninvasive methods of visualizing and quantifying early cartilage degeneration. PURPOSE: To determine the tibiofemoral biomechanical alterations before and after ACL reconstruction using magnetic resonance imaging (MRI) and to evaluate the association between biomechanics and cartilage degeneration using T(1ρ) and T(2). STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Knee MRIs of 51 individuals (mean age, 29.5 ± 8.4 years) with unilateral ACL injuries were obtained prior to surgery; 19 control subjects (mean age, 30.7 ± 5.3 years) were also scanned. Follow-up MRIs were obtained at 6 months and 1 year. Tibial position (TP), internal tibial rotation (ITR), and T(1ρ) and T(2) were calculated using an in-house Matlab program. Student t tests, repeated measures, and regression models were used to compare differences between injured and uninjured sides, observe longitudinal changes, and evaluate correlations between TP, ITR, and T(1ρ) and T(2). RESULTS: TP was significantly more anterior on the injured side at all time points (P < .001). ITR was significantly increased on the injured side prior to surgery (P = .033). At 1 year, a more anterior TP was associated with elevated T(1ρ) (P = .002) and T(2) (P = .026) in the posterolateral tibia and with decreased T(2) in the central lateral femur (P = .048); ITR was associated with increased T(1ρ) in the posteromedial femur (P = .009). ITR at 6 months was associated with increased T(1ρ) at 1 year in the posteromedial tibia (P = .029). CONCLUSION: Persistent biomechanical alterations after ACL reconstruction are related to significant changes in cartilage T(1ρ) and T(2) at 1 year postreconstruction. Longitudinal correlations between ITR and T(1ρ) suggest that these alterations may be indicative of future cartilage injury, leading to degeneration and osteoarthritis. CLINICAL RELEVANCE: Newer surgical techniques should be developed to eliminate the persistent anterior tibial translation commonly seen after ACL reconstruction. qMR will be a useful tool to evaluate the ability of these newer techniques to prevent cartilage changes.