Predictors of Manipulation Under Anesthesia After Knee Arthroplasty in the United States Military Health System

Background: Stiffness after knee arthroplasty is commonly treated with manipulation under anesthesia (MUA). Previously identified predictors of MUA include younger age, Black race, low body mass index, diabetes, tobacco use, and prior nonarthroplasty knee surgery. Whether these factors persist in a healthcare system with minimal financial barriers remains unclear. We evaluated rates and predictors of MUA in the U.S. Military Health System (MHS). Methods: This retrospective cohort study queried the MHS Data Repository for patients undergoing primary total knee arthroplasty, revision total knee arthroplasty (rTKA), or unicompartmental knee arthroplasty (UKA) from 2016 to 2022 using Current Procedural Terminology. Minimum follow-up was 6 months. Logistic regression evaluated associations between patient factors and MUA. Results: A total of 8223 knee arthroplasties were identified in 7164 patients. Mean age was 62 ± 9 years; active-duty patients (n = 502) averaged 48 ± 7 years. MUA rates were 4.6% after TKA (315/6833), 2.1% after rTKA (19/885), and 1.4% after UKA (7/505). Protective factors included older age (odds ratio [OR] 0.96/year, P < .0001), UKA (OR 0.23, P = .0002), and rTKA (OR 0.41, P = .0002). Risk factors included Black race (OR 1.90, P < .0001), prior nonarthroplasty knee surgery (OR 1.56, P = .04), and diabetes (OR 1.40, P = .01). Tobacco use and active-duty status were not significant predictors. Mean follow-up was 3 years. No statistically significant association between MUA and revision arthroplasty was detected. Conclusions: Previously identified risk factors, including younger age, Black race, diabetes, and prior knee surgery, remained associated with MUA within the MHS. Active-duty status was not associated with increased MUA risk.