Manipulation under anesthesia after unicompartmental knee arthroplasty: incidence and risk factors

Extensive literature exists on the incidence and risk factors for manipulation under anesthesia (MUA) following total knee arthroplasty (TKA); however, data for MUA following unicompartmental knee arthroplasty (UKA) has not previously been reported. The purpose of this study is to describe the incidence and risk factors for MUA after UKA.

This retrospective cohort study using the Medicare Limited Data Set included patients who underwent UKA from 2016 to 2019. The primary outcome was MUA within one year of UKA. A mixed-effects multivariable model measured the association between age, race, sex, hospital location/region, Deyo-Charlson comorbidity index, obesity (BMI > 30), smoking status, and MUA outcomes. Odds ratios (OR) and 95% confidence intervals (CI) were reported.

Of 41,220 total patients, 140 (0.34%) underwent MUA within one year of UKA. Median time from UKA to MUA was 2.02 months (IQR 1.61-2.78). Black patients had higher odds of MUA compared to White patients (OR 3.11, 95% CI 1.54-6.27, P = 0.002). Females had lower odds of MUA (OR 0.63, 95% CI 0.44-0.89, P = 0.008). For each year of increase in age, there was a 5% decrease in odds of MUA (OR 0.95, 95% CI 0.92-0.98, P = 0.001). The Deyo-Charlson comorbidity index, obesity and smoking were not associated with MUA.

The incidence of MUA following UKA is lower than that observed in the TKA literature. Patient age, race, and sex were associated with higher MUA odds while medical comorbidities and modifiable risk factors were not.