Short-term and long-term in vivo 3D kinematics of the knee joint during split squat after anterior cruciate ligament reconstruction.

BACKGROUND

Early-onset knee osteoarthritis and high reinjury rates after anterior cruciate ligament reconstruction (ACLR) highlight the need to monitor knee joint mechanics over time. Understanding long-term structural changes post-ACLR can clarify mechanisms underlying early degeneration. This study investigated short- and long-term changes in knee arthrokinematics during split squat post-ACLR.

METHODS

Sixteen individuals with ACLR (8 short-term, ∼3 years; 8 long-term, ∼12 years) and 8 healthy controls performed split squats while undergoing single-plane fluoroscopy. Individualized 3D models of the distal femur and proximal tibia were created using computed tomography (CT) scans. The 3D positions and orientations of the femur and tibia were determined via 2D/3D model-image registration. A two-way repeated measures analysis of variance (ANOVA) compared tibial translation and rotation relative to the femur. Contact points of the medial and lateral femoral condyles on the tibial plateau were also compared between groups.

FINDINGS: The long-term group exhibited significantly greater anterior tibial translation relative to the femur compared to controls during the split squat (Mean difference [95% CI]: 4.63 mm [1.77, 7.50]). Additionally, the medial contact point in the long-term group was located more anteriorly than in healthy knees (Mean difference [95% CI]: 5.45 mm [2.46, 8.43]).

INTERPRETATION: Increased anterior tibial translation and altered contact locations suggest persistent structural instability and abnormal joint loading approximately 10 years after ACLR. These findings underscore the importance of long-term surveillance and targeted prevention strategies to reduce the risk of joint degeneration following ACLR.