A High-Riding Patella Is a Feature of Knee Joint Motion During Gait After ACL Reconstruction

Accurate measurements of knee joint motion during gait after anterior cruciate ligament reconstruction (ACLR), especially for the patellofemoral joint, are sparse. The aim of this study was to measure six-degree-of-freedom (6-DOF) patellofemoral and tibiofemoral motion in ACLR and uninjured contralateral knees during gait, and to compare these results to healthy (control) knees. Biplane fluoroscopy was used to measure 6-DOF patellofemoral and tibiofemoral motion in 15 ACLR participants (26.3 +/- 3.9 years) for complete cycles of level walking and downhill walking, and the results were compared to data for 10 healthy individuals (29.8 +/- 6.1 years). Mean patellar superior translation, anterior translation, and flexion over the gait cycle were respectively 4.4-5.6 mm greater, 5.4-6.3 mm greater, and 3.7 degrees-7.0 degrees less in the ACLR and contralateral knees compared to controls across both activities (p < 0.021). Articular contact was 7.6 mm higher on the femoral trochlea in the ACLR and contralateral knees compared to controls. The patellar tendon was 8.9 mm longer (p < 0.001) in the ACLR and contralateral knees compared to controls. Among ACLR participants, 14 out of 30 knees (47%) had an Insall-Salvati ratio >= 1.20, indicating patella alta. Mean tibial external rotation and anterior translation over the gait cycle were respectively 3.4 degrees-3.8 degrees greater and 2.6-3.0 mm greater in the ACLR knee compared to controls across both activities (p < 0.025). A high-riding patella in both knees of the ACLR participants was due to a longer patellar tendon. A change in the load-bearing areas of the femoral trochlea may contribute to the high rate of patellofemoral osteoarthritis seen after ACLR.