Predicting risk of unplanned subsequent knee surgery following ACL reconstruction

Following anterior cruciate ligament reconstruction (ACLR), unplanned subsequent knee surgeries are disruptive and costly. The purpose of this study was to identify risk factors associated with any subsequent knee surgery as well as specific surgical procedures, including revision, contralateral ACLR, surgery for meniscus injury, or procedure for loss of motion following primary ACLR using data from the electronic health record (EHR) of a large single-system health network.

Data for individuals (≥14 years old) who underwent primary ACLR between January 2013 and June 2021 were extracted from the EHR. Potential patient and surgical predictors were identified from structured data and/or extracted from the ACLR operative report using natural language processing. Cox proportional hazards models were used to identify factors associated with the overall risk of subsequent knee surgery as well as specific surgical procedures (p < 0.05). Incidence per 100 person-years was reported.

From an initial sample of 6,121 individuals, 3,478 (median 21.8 years old [IQR 17.4, 32.9]; 44.2% female) underwent primary ACLR and were eligible for this study. The incidence rate per 100 person-years was 12.3 for any subsequent knee surgery, 2.7 for revision, 2.3 for contralateral ACLR, 4.3 for subsequent meniscus surgery, and 2.7 for subsequent procedure for loss of motion. No model was successful in identifying risk factors associated with any subsequent knee surgery. Risk factors associated with revision included younger age, medium surgeon volume compared with high volume (12-45 mean cases/year vs. ≥ 46), and sex as a time-varying coefficient (TVC), indicating females were initially at lower risk but risk increased with time. The only significant risk factor identified for subsequent contralateral ACLR was younger age as a TVC. Significant risk factors for subsequent meniscus surgery included younger age, medium surgeon volume compared with high volume, and medial meniscus repair at the time of primary ACLR. Risk factors for subsequent procedure for loss of motion included female sex, Black race, lateral meniscus repair, and quadriceps tendon autograft, while medial meniscectomy was found to be protective compared with no medial meniscus surgery.

Risk factors varied by specific type of subsequent surgery following primary ACLR. Specifically, younger age was a risk factor for future ACL surgery, medium surgeon volume was associated with an increased risk of revision and subsequent meniscus surgery, medial meniscus repair was a risk factor for subsequent meniscus surgery, and lateral meniscus repair was a risk factor for a subsequent procedure for loss of motion. Consideration of risk factors relevant to subsequent surgeries beyond revision alone may better inform patient counseling prior to ACLR, as well as risk stratification and individualized post-operative rehabilitation following ACLR.