Background
Anterior cruciate ligament (ACL) injury is considered a risk factor for osteoarthritis.
Aim
The primary aim of the study was to investigate the cumulative risk and risk factors associated with a subsequent knee arthroplasty (KA) after an ACL reconstruction. The secondary aim was to compare the relative risk for KA after ACL reconstruction compared with the general population.
Methods
Cumulative risk and possible risk factors for KA after ACL reconstruction were analyzed by combining data from two national registries, the Norwegian Knee Ligament Register and the Norwegian Arthroplasty Register in a Cox regression model. The relative risk of KA for ACL patients compared with the general population was calculated in stratified age groups.
Results
One hundred and one knees underwent KA out of the eligible study population of 25,931 knees. We found a 0.5% (CI: 0.4-0.6) cumulative risk of KA 10 years after ACL reconstruction. The cumulative risk of knee replacement was significantly higher in patients who were older at the time of their index ACL reconstruction. Revision of the ACL (HR: 4.8, CI: 2.6, 8.9), deep cartilage injury, ICRS (International Cartilage Repair Society) 3-4 (HR: 3.9, CI: 2.4, 6.3) and two-year post-operative KOOS Sport/Rec sub-score<44 (HR: 3.6, CI: 1.7, 7.7) were important risk factors for KA surgery. We found a higher risk of KA at the age of 30-39 years after a previous ACL reconstruction compared to the general population (RR: 3.4 (CI: 1.6-7.1))
Discussion
Some comparable studies have found a slightly higher risk of KA after 10 years than our study, but indications for KA may vary between countries.
Conclusion
Ten years after an ACL reconstruction, the overall cumulative risk of KA was 0.5%. Revised ACL reconstruction, cartilage injury at time of ACL reconstruction and KOOS (two years post-operatively, Sport/Rec) <44 were major risk factors for subsequent KA. Patients with previous ACL surgery at age 30-39 had a 3.4 times higher risk of KA than the general population.
Level of Evidence: level II prospective cohort study.