AJSM Webinar Series: ACL Injury and PTOA: Bridging Biology, Imaging, and Machine Learning to Improve Outcomes-Lu Y et al. Posttraumatic Arthritis After ACL Injury: Machine Learning Comparison Between Surgery and Nonoperative Management. AJSM 2025. PMID: 40079334

Lu Y et al. Posttraumatic Arthritis After ACL Injury: Machine Learning Comparison Between Surgery and Nonoperative Management. AJSM 2025. PMID: 40079334

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This study compared long-term knee outcomes after primary ACL injury in patients treated with ACL reconstruction (ACLR) versus nonoperative care, using machine learning–based causal inference methods on a Rochester Epidemiology Project cohort. The final sample included 1,194 patients with at least 7.5 years of follow-up: 974 underwent ACLR and 220 were treated without surgery.<br /><br />At follow-up, symptomatic posttraumatic osteoarthritis (PTOA) developed in 22.1% of the ACLR group versus 63.6% of the nonoperative group. Total knee arthroplasty (TKA) was also less common after ACLR (2.6% vs 22.6%), and occurred later in the surgical group. After adjusting for confounders with targeted maximum likelihood estimation (TMLE), ACL reconstruction was associated with an 11% reduction in the risk of PTOA compared with nonoperative treatment. However, ACLR did not show a significant effect on progression to TKA in the causal inference model.<br /><br />Time-to-event analyses using random survival forests showed that ACLR delayed both the onset of PTOA and progression to TKA. Important risk factors for worse outcomes, regardless of treatment, included older age at injury, higher body mass index, more prior arthroscopic knee surgeries, residual laxity at follow-up, and concomitant meniscal or cartilage injury. Sedentary activity and greater pain at presentation also contributed to risk.<br /><br />The authors conclude that ACL reconstruction has a measurable protective effect against PTOA and delays joint degeneration compared with nonoperative management, though it does not clearly reduce eventual TKA risk. They note that older age, BMI, secondary surgeries, and residual instability remain key predictors of poor long-term knee health.

Keywords

ACL reconstruction

nonoperative treatment

posttraumatic osteoarthritis

total knee arthroplasty

causal inference

targeted maximum likelihood estimation

random survival forests

knee injury outcomes

meniscal injury

body mass index