Persons Who Have Undergone ACL Reconstruction Exhibit Altered Patellofemoral Joint Contact Area: Implications For Early Onset Patellofemoral Joint Arthritis

Early onset patellofemoral joint (PFJ) osteoarthritis is prevalent among persons who have undergone anterior cruciate ligament reconstruction (ACLR). Reduced contact between patella and trochlear groove has been associated with increased patellofemoral joint stress and has been proposed to contribute to patellar cartilage pathology. PFJ contact area has been reported to be influenced by patellar alignment, patellar height, and bony morphology. PURPOSE: To compare PFJ contact area in females who have undergone ACLR and healthy age and sex matched controls. A secondary purpose was to identify anatomical and alignment predictor(s) of reduced contact area. METHODS: Magnetic resonance images (1.5-T Signa scanner) were obtained from 30 female participants (15 ACLR, 15 controls). Axial and sagittal plane images were obtained using a 3D SPGR sequence at 20 degrees of knee flexion under loaded conditions (35% bodyweight). Using previously described methods, contact area was measured from the axial plane images. Additionally, structural and alignment variables (lateral patellar tilt and displacement, sulcus angle, lateral trochlear inclination angle, and patellar height (Insall-Salvati ratio) were measured from both axial and sagittal plane images. An independent t-test was used to compare total cartilage contact area between groups. Stepwise regression was used to determine the best predictor of contact area among the alignment and structural measures obtained. RESULTS: The ACLR group exhibited significantly lower total contact area compared to the control group (199.4 mm2 ± 72.4mm2 vs. 274.3 mm2 ± 103.5 mm2, p = 0.003). Stepwise regression revealed lateral patellar tilt was the only predictor of contact area (R2 = 0.40, p < 0.001). CONCLUSION: Females post ACLR exhibit reduced PFJ contact area compared to healthy controls. Increased lateral patellar tilt appears to underlie the reduction in contact area, potentially influencing location and magnitude of patellofemoral joint stress.