Patellofemoral and tibiofemoral joint loading during a single-leg forward hop following ACL reconstruction

Altered biomechanics are frequently observed following anterior cruciate ligament reconstruction (ACLR). Yet, little is known about knee-joint loading, particularly in the patellofemoral-joint, despite patellofemoral-joint osteoarthritis commonly occurring post-ACLR. This study compared knee-joint reaction forces and impulses during the landing phase of a single-leg forward hop in the reconstructed knee of people 12-24 months post-ACLR and uninjured controls. Experimental marker data and ground forces for 66 participants with ACLR (28 ± 6 years, 78 ± 15 kg) and 33 uninjured controls (26 ± 5 years, 70 ± 12 kg) were input into scaled-generic musculoskeletal models to calculate joint angles, joint moments, muscle forces, and the knee-joint reaction forces and impulses. The ACLR group exhibited a lower peak knee flexion angle (mean difference: −6°; 95% confidence interval: [−10°, −2°]), internal knee extension moment (−3.63 [−5.29, −1.97] percentage of body weight × participant height (body weight [BW] × HT), external knee adduction moment (-1.36 [−2.16, −0.56]% BW × HT) and quadriceps force (−2.02 [−2.95, −1.09] BW). The ACLR group also exhibited a lower peak patellofemoral-joint compressive force (−2.24 [−3.31, −1.18] BW), net tibiofemoral-joint compressive force (−0.74 [−1.20, 0.28] BW), and medial compartment force (−0.76 [−1.08, −0.44] BW). Finally, only the impulse of the patellofemoral-joint compressive force was lower in the ACLR group (−0.13 [−0.23, −0.03] body weight-seconds). Lower compressive forces are evident in the patellofemoral- and tibiofemoral-joints of ACLR knees compared to uninjured controls during a single-leg forward hop-landing task. Our findings may have implications for understanding the contributing factors for incidence and progression of knee osteoarthritis after ACLR surgery.