Patient and Operative Risk Factors for Subsequent Knee Arthroplasty After Primary Anterior Cruciate Ligament Reconstruction: A Cohort Study of 52,222 Patients

Background: Knee arthroplasty in patients who have undergone anterior cruciate ligament reconstruction (ACLR) has been associated with a high risk of infection, arthrofibrosis, and longer operative time due in part to difficulty with exposure and retained hardware. Patients who undergo ACLR are at a higher risk of undergoing knee arthroplasty and are at risk earlier than the general population. As patients with ACLR age and as ACLR surgery becomes more prevalent in the older athlete, the rates of knee arthroplasty after ACLR will only increase. Purpose: To determine the incidence of knee arthroplasty after ACLR, as well as identify patient and operative risk factors for knee arthroplasty after ACLR. Study Design: Cohort study; Level of evidence 3. Methods: Data from Kaiser Permanente’s ACLR Registry and Total Joint Replacement Registry were used to conduct a cohort study. Patients with primary ACLR were identified (2005-2022). Patient factors considered included age, body mass index (BMI), sex, race/ethnicity, smoking status, American Society of Anesthesiologists classification, activity at the time of injury, and medical comorbidities. Time from injury to ACLR, concomitant meniscal or chondral injuries, multiligament injury, graft type, and drilling technique were procedure factors evaluated. Postoperative factors included revision surgery, ipsilateral reoperation, and contralateral operation during follow-up. The outcome of interest was a subsequent knee arthroplasty. Patients were followed until the outcome of interest unless censored for membership disenrollment, death, or study end date (December 31, 2022). Multivariable Cox proportional hazards regression was used to determine factors associated with knee arthroplasty after ACLR using a P value <.05 as the threshold for statistical significance. Results: The study sample included 52,222 primary ACLRs. The mean age was 28.6 years, and more patients were male (60.2%). The incidence of knee arthroplasty after ACLR was 1.60% at 15 years of follow-up. The mean age of patients undergoing knee arthroplasty after ACLR was 56 years, which was 12 years younger than the mean age of patients undergoing primary knee arthroplasty in general. Risk factors for knee arthroplasty included increasing age compared with those <40 years (40-49 years: hazard ratio [HR], 8.03 [95% CI, 4.83-13.34]; 50-59 years: HR, 18.24 [95% CI, 10.56-31.52]; ≥60 years: HR, 53.77 [95% CI, 26.24-110.22]), increasing BMI (HR, 1.07 [95% CI, 1.04-1.10]), female sex (HR, 1.60 [95% CI, 1.21-2.12]), trauma-associated anterior cruciate ligament (ACL) injury (HR, 1.71 [95% CI, 1.07-2.74]), a history of hypertension (HR, 1.69 [95% CI, 1.14-2.51]) or other neurological disorders at the time of ACLR (HR, 5.08 [95% CI, 2.15-12.02]), chondral injuries reported during the ACLR (HR, 1.43 [95% CI, 1.04-1.97]), and allograft selection (HR, 2.16 [95% CI, 1.17-4.00]). Revision surgery (HR, 2.19 [95% CI, 1.18-4.08]), ipsilateral reoperation (HR, 3.50 [95% CI, 2.43-5.05]), and contralateral surgery (HR, 4.06 [95% CI, 2.59-6.35]) during follow-up were risk factors for knee arthroplasty. Conclusion: Increasing age was the strongest risk factor for subsequent knee arthroplasty in patients who have undergone prior ACLR. Patients should be counseled that undergoing ACLR with allograft had a 2 times higher risk of future knee arthroplasty compared with patellar tendon autograft. Additional independent risk factors identified included female sex, increasing BMI, a history of hypertension or other neurological disorders, trauma-related injury compared with sports injury, concomitant chondral injury, and revision surgery, ipsilateral reoperation, or contralateral surgery during follow-up.