Poor Performance on Single-Legged Hop Tests Associated With Development of Posttraumatic Knee Osteoarthritis After Anterior Cruciate Ligament Injury

BACKGROUND: The risk for knee osteoarthritis (OA) is substantially increased after anterior cruciate ligament (ACL) injury. Tools are needed to identify characteristics of patients after ACL injury who are most at risk for posttraumatic OA. PURPOSE: To determine whether clinical measures of knee function after ACL injury are associated with the development of radiographic knee OA 5 years after injury. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 76 athletes (mean age, 28.7 ± 11.3 years; 35.5% female) with ACL injury were included. Clinical measures of knee function (quadriceps strength, single-legged hop tests, patient-reported outcomes) were assessed after initial impairment resolution (baseline), after 10 additional preoperative or nonoperative rehabilitation sessions (posttraining), and 6 months after ACL reconstruction or nonoperative rehabilitation. Posterior-anterior bent-knee radiographs were completed at 5 years and graded in the medial compartment by use of the Kellgren-Lawrence system. Logistic regression models were used at each of the 3 time points to determine the ability of clinical measures to predict knee OA at 5 years. RESULTS: Of the 76 patients, 9 (11.8%) had knee OA at 5 years. After adjustment for ACL reconstruction compared with nonoperative management, ipsilateral second ACL injuries, and the presence of contralateral knee OA, clinical measures of knee function at posttraining (6-m timed hop, Knee Outcomes Survey–Activities of Daily Living Scale) explained the most variance in posttraumatic OA development at 5 years (P = .006; ▵R (2), 27.5%). The 6-m hop test was the only significant posttraining predictor of OA at 5 years (P = .023; patients without OA, 96.6% ± 5.4%; patients with OA, 84.9% ± 14.1%). Similar significant group differences in hop scores and subjective knee function were present at baseline. No significant group differences in clinical measures existed at 6 months after ACL reconstruction or nonoperative rehabilitation. CONCLUSION: Poor performance in single-legged hop tests early after ACL injury but not after reconstruction or nonoperative rehabilitation is associated with the development of radiographic posttraumatic knee OA 5 years after injury. Clinical measures of knee function were most predictive of subsequent OA development following an extended period of rehabilitation early after ACL injury.