Females who have undergone anterior cruciate ligament reconstruction exhibit altered patellofemoral joint contact area and alignment.

Abstract

Lateral patella tilt and displacement have been reported to be associated with increased risk for early-onset osteoarthritis post ACL reconstruction. It is conceivable that altered patella alignment may expose these individuals to excessive joint stress owing to a reduction in contact area between the patella and trochlear surface of the femur. Therefore, our study objectives were: 1) to compare patellofemoral joint contact area and patellar alignment between females post-ACL reconstruction and healthy controls, and 2) to assess associations between measures of patellar alignment and contact area. Forty females between the ages of 18-35 (20 post-ACL reconstruction, 20 matched controls) underwent MR imaging of the patellofemoral joint at 0°, 20°, 40°, and 60° of knee flexion under loaded conditions (35 % bodyweight). Patellofemoral joint contact area, lateral patella tilt and lateral patella displacement were compared between groups and knee flexion angles using repeated measures analysis of variance tests. Pearson correlations evaluated associations between patella alignment and contact area at each knee flexion angle. Compared to the control group, females post ACL reconstruction exhibited significantly reduced contact area (differences ranging from 21.6 % to 29.1 %), and elevated lateral patella tilt (differences ranging from 3.7° to 4.9°). No differences in lateral patellar displacement were observed. Lateral patellar tilt was negatively correlated with contact area across all knee angles (r-values ranging from -0.32 to -0.66). Reduced contact area highlights a potential mechanism by which patellar alignment may be contributory to early cartilage changes post ACL reconstruction.