Patient and Operative Risk Factors for Osteoarthritis After Primary Anterior Cruciate Ligament Reconstruction: A Cohort Study of 41,976 Patients

Background: The reported incidence of posttraumatic knee osteoarthritis (PTOA) after primary anterior cruciate ligament reconstruction (ACLR) varies considerably. Further, there are gaps in identifying which patients are at risk for PTOA after ACLR and whether there are modifiable factors. Purpose: To (1) determine the incidence of PTOA in a primary ACLR cohort and (2) identify patient and perioperative factors associated with the development of PTOA after primary ACLR. Study Design: Cohort study; Level of evidence, 3. Methods: Data from the Kaiser Permanente ACLR Registry were used to conduct a cohort study. Patients who had undergone primary ACLR without a previous diagnosis of osteoarthritis were identified (2009-2020). The crude incidence of PTOA was calculated using the Aalen-Johansen estimator with a multistate model. The association of patient and operative factors with the development of PTOA after primary ACLR was modeled as a time to event using multistate Cox proportional hazards regression. Models stratified by age (<22 and >= 22 years) were also conducted because of the effect modification of age. Results: The study sample included 41,976 cases of primary ACLR. The incidence of PTOA was 1.7%, 5.1%, and 13.6% at 2, 5, and 10 year follow-ups, respectively. Risk factors for PTOA that were consistently identified in the overall cohort and age-stratified groups included a body mass index >= 30 versus <30 and an allograft or quadriceps tendon autograft versus a hamstring tendon autograft. Patients presenting with knee pain after ACLR were further identified when considering postoperative factors. Other risk factors for PTOA in the overall cohort included age >= 22 versus <22 years, bone-patellar tendon-bone autograft versus hamstring tendon autograft, hypertension, cartilage injury, meniscal injury, revision after primary ACLR with concomitant meniscal/cartilage surgery, multiligament injury, other activity at the time of injury compared with sport, and tibial tunnel drilling technique rather than the anteromedial portal. Conclusion: Knee pain after ACLR may be an early sign of PTOA. Surgeons should consider the adverse associations of a higher body mass index and an allograft or quadriceps tendon autograft with the development of PTOA, as these were factors identified with a higher risk, regardless of a patient's age at the time of primary ACLR.