Early Changes in Knee Center of Rotation During Walking After Anterior Cruciate Ligament Reconstruction Correlate With Later Changes in Patient-Reported Outcomes

Background: Altered knee kinematics after anterior cruciate ligament injury and reconstruction (ACLR) have been implicated in the development of posttraumatic osteoarthritis (PTOA), leading to poor long-term clinical outcomes. Purpose: This study was conducted to determine (1) whether the average knee center of rotation (KCOR), a multidimensional metric of knee kinematics, of the ACL-reconstructed knee during walking differs from that of the uninjured contralateral knee; (2) whether KCOR changes between 2 and 4 years after surgery; and (3) whether early KCOR changes predict patient-reported outcomes 8 years after ACLR. Study Design: Descriptive laboratory study. Methods: Twenty-six human participants underwent gait analysis with calculation of bilateral KCOR during walking at 2 and 4 years after unilateral ACLR. Knee injury and Osteoarthritis Outcome Score (KOOS) and Lysholm score results were collected at 2, 4, and 8 years after ACLR in 13 of these participants. Results: The ACL-reconstructed knee showed greater medial compartment motion because of pivoting about a more lateral KCOR (P = .03) than the contralateral knee at 2 years. KCOR became less lateral over time (P = .047), with values approaching those of the uninjured knee by 4 years (P = .55). KCOR was also more anterior in the ACL-reconstructed knee at 2 years (P = .02). Between 2 and 4 years, KCOR moved posteriorly in 16 (62%) and anteriorly in 10 (38%) participants. Increasing the anterior position of KCOR in the ACL-reconstructed knee from 2 to 4 years correlated with worsening clinical outcomes at 4 years (KOOS-Quality of Life, R-2 = 0.172) and more strongly at 8 years (Lysholm score, R-2 = 0.41; KOOS-Pain, R-2 = 0.37; KOOS-Symptoms, R-2 = 0.58; and KOOS-Quality of Life, R-2 = 0.50). Conclusion: The observed changes to KCOR during walking between 2 and 4 years after ACLR show progressive improvement toward kinematic symmetry over the 2-year follow-up. The correlation between increasingly abnormal kinematics and worsening clinical outcomes years later in a subset of participants provides a potential explanation for the incidence of PTOA after ACLR.