Patellofemoral Joint Contact Area During Gait is Significantly Reduced in ACL-reconstructed and Uninjured Contralateral Knees Compared to Healthy Controls.

This study aimed to measure patellofemoral (PF) joint contact area for complete cycles of walking in both knees of individuals who had undergone unilateral anterior-cruciate-ligament reconstruction (ACLR) 6-15 months earlier. Computed tomography, magnetic resonance imaging, and biplane X-ray fluoroscopy were combined to determine PF contact area in the ACLR and uninjured contralateral knees of 15 individuals (26.3 ± 3.9 years) during level walking and downhill walking, and the results were compared to data for 10 healthy controls (29.8 ± 6.1 years). PF contact areas in ACLR and contralateral knees were comparable across the gait cycle for both activities, with total, lateral, and medial PF contact areas all increasing with knee flexion and reaching peak values of 560-595 mm2, 399-424 mm2, and 171-196 mm2 respectively. Lateral contact area was consistently larger than medial contact area in ACLR, contralateral, and healthy knees. However, compared to healthy knees, PF contact areas in ACLR and contralateral knees were substantially smaller (25% - 80% lower) throughout the gait cycle in both activities. On average, total, lateral, and medial PF contact areas in ACLR and contralateral knees were approximately one-half of those in healthy knees (p < 0.001). The primary factor contributing to this reduction was a more superiorly positioned patella on the trochlea (high-riding patella), which correlated strongly with PF contact area (r = - 0.83, p < 0.001). Patellar lateral tilt also contributed to the reduction in PF contact area, showing a moderate correlation (r = - 0.44, p < 0.001). These results may be combined with calculations of PF contact force to evaluate PF joint stress in ACLR, contralateral, and healthy knees during gait.