Rates of knee arthroplasty in anterior cruciate ligament reconstructed patients: a longitudinal cohort study of 111,212 procedures over 20 years

Background and Purpose
Long-term rates of knee arthroplasty in patients with anterior cruciate ligament (ACL) injury, undergoing ligament reconstruction (ACLr), have been unclear. The purpose of this study was to determine this risk of arthroplasty with comparison to the general population.

Patients and Methods
All patients undergoing an ACLr in England, 1997/98-2016/17, were identified from national hospital statistics. Patients subsequently undergoing a knee arthroplasty were identified and survival analysis was performed (survival without undergoing knee arthroplasty). A cox proportional hazards model was used to identify factors associated with knee arthroplasty. Relative risk of knee arthroplasty (total or partial) in comparison to the general population was determined.

Results
111,212 ACLr patients were eligible for analysis (mean age 29; 77% male). Overall, 0.46% (95% confidence interval [CI] 0.40-0.52) ACLr patients underwent knee arthroplasty within 5-years, 0.97% (CI 0.82-1.2) within 10-years, and 1.8% (CI 1.4-2.3) within 15-years. Knee arthroplasty risk was greater in older age groups and females. In comparison to the general population, the relative risk of undergoing arthroplasty at a younger age was elevated: at 30-39-years (risk ratio [RR] 19.6; CI 11.1-34.7), 40-49-years (RR 7.5; CI 5.5-10.2), and 50-59-years (RR 2.5; CI 1.8-3.5), but not 60-69-years (RR 1.7; CI 0.93-3.2).

Interpretation
Patients sustaining an ACL injury, undergoing ACLr, are at elevated risk of subsequent knee arthroplasty in comparison to the general population. Although the absolute rate of arthroplasty is low, the risk of arthroplasty at a younger age is particularly elevated. When the outcome of shared decision-making is ACLr, this data will help inform patients and clinicians about the long-term risk of requiring knee arthroplasty.