O’Donoghue Award Winner: Early Changes in the Knee Joint Center of Rotation during Walking Following 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 premature osteoarthritis (OA), leading to poor long term clinical outcomes. PURPOSE: This study was performed to determine (1) whether average knee center of rotation (KCOR), a multidimensional metric of knee kinematics, of the ACLR knee during walking differs from that of the contralateral uninjured 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: Prospective Clinical Study. METHODS: Twenty-six human subjects underwent gait analysis with calculation of bilateral KCOR during walking at 2 and 4 years after unilateral ACLR. Knee injury and Osteoarthritis Outcome Scores (KOOS) and Lysholm scores were collected at 2, 4, and 8 years after ACLR in 13 of these subjects. RESULTS: The ACLR knee showed greater medial compartment motion due to pivoting about a more lateral KCOR (P=0.03) than the uninjured contralateral knee at 2 years. KCOR moved medially over time (P=0.047), with values approaching those of the uninjured knee by 4 years (P=0.55). KCOR was also more anterior in the ACLR knee at 2 years (P=0.02). Between 2 and 4 years, KCOR moved posteriorly in 16 (62%) and anteriorly in 10 (38%) subjects. Increasing anterior position of KCOR in the ACLR knee from 2 to 4 years showed no correlation with clinical outcomes at 4 years but correlated with worsening clinical outcomes at 8 years: Lysholm (R2=0.41); KOOS pain (R2=0.37), symptoms (R2=0.58), and quality of life (R2=0.50). CONCLUSIONS: The observed changes to KCOR during walking between 2 and 4 years after ACLR show progressive improvement suggestive of continued graft maturation and neuromuscular recovery. The finding of increasingly abnormal kinematics correlating with reduced clinical outcomes years later in a subset of subjects provides a potential explanation for the incidence of premature OA following ACLR. These findings support progressing to more comprehensive studies of larger cohorts examining the predictive potential of KCOR for OA risk as measured by advanced quantitative imaging and radiographs. CLINICAL RELEVANCE: These results suggest that changes to KCOR during walking as derived from gait analysis, a clinically available metric, may provide early warning of deteriorating knee function after ACLR years before the onset of clinical symptoms.