Degenerative changes in cartilage likely occur in the medial compartment after anterior cruciate ligament reconstruction

Purpose Magnetic resonance imaging with T1 rho mapping is used to quantify the amount of glycosaminoglycan in articular cartilage, which reflects early degenerative changes. The purposes of this study were to evaluate early degenerative changes in knees after anterior cruciate ligament (ACL) reconstruction by comparing T1 rho values before and 2 years after surgery and investigate whether surgical factors and clinical outcomes are related to differences in T1 rho values. Methods Fifty patients who underwent unilateral primary ACL reconstruction were evaluated using T1 rho mapping before and 2 years after surgery. Three regions of interest (ROIs) were defined in the cartilage associated with the medial (M) and lateral (L) weight-bearing areas of the femoral condyle (FC) (anterior: MFC1 and LFC1, middle: MFC2 and LFC2, and posterior: MFC3 and LFC3). Two ROIs associated with the tibial plateau (T) were defined (anterior: MT1 and LT1, and posterior: MT2 and LT2). T1 rho values within the ROIs were measured before and 2 years after surgery and compared using the paired t test. Correlations between the difference in T1 rho values at these two time points and patient characteristics, presence of a cartilaginous lesion, graft type, and postoperative anteroposterior laxity were also evaluated using Pearson's and Spearman's correlation coefficients. Results There was a significant increase in T1 rho before versus 2 years after surgery in the MT1, MT2, LFC1, and LT1 areas, and a significant decrease in the LFC3 and LT2 areas. There was a significant correlation between postoperative anterior-posterior laxity and a postoperative increase in T1 rho values in the MFC3 (r = 0.37, P = 0.013) and MT2 (r = 0.35, P = 0.021) areas. Increases in T1 rho values in the MFC2 area were negatively correlated with KOOS symptoms (rho = - 0.349, P = 0.027) and quality of life (rho = - 0.374, P = 0.017) subscale scores. Conclusion Early degenerative changes in medial articular cartilage were observed with T1 rho mapping at 2 years after ACL reconstruction. Postoperative anterior-posterior laxity is correlated with an increase in T1 rho values in the posteromedial femur and tibia. An increase in T1 rho values in the central medial femoral condyle was associated with knee symptoms.