Introduction

Unicompartmetnal knee arthroplasty (UKA) can be safely performed as an outpatient procedure or with a limited single night hospital stay. However, a percentage of patients require a prolonged hospital length of stay (LOS) following UKA. With many UKA being performed in ambulatory surgery settings it is important to know which patients are at risk for prolonged LOS and non-home discharge. The purpose of this study was to identify the incidence and risk factors for prolonged LOS and non-home discharge following UKA.

Methods

The American College of Surgeons National Surgical Quality Improvement Program (NSQIP) registry was queried to identify patients who underwent primary UKA from 2011 to 2018. Demographics, comorbidities, preoperative lab values, operative time, discharge destination and LOS were analyzed. Prolonged LOS was defined as patients that were admitted for 2 or more nights and non-home discharge was defined as discharge to rehabilitation facility, skilled nursing facility, or unskilled nursing facility. Multiple logistic regression analyses were performed to identify risk factors for prolonged LOS and non-home discharge, with significance defined as p<0.05.

Results

Overall, 11,227 cases of UKA (49% male) were identified during the study period. The incidence of prolonged LOS was 40% (n=4,444) and non-home discharge was 6% (n=638). The multivariate model identified preoperative functional dependency (Odds ratio [OR]: 2.5, 95% Confidence Interval [CI]: 1.6-3.8, p<0.01), age =80 years (OR: 2.0, 95% CI: 1.6-2.5, p<0.01), and operative time >90 mins (OR: 1.7, 95% CI: 1.6-1.9, p<0.01) as the strongest predictors for prolonged LOS after UKA. Additionally, female sex, obesity, diabetes mellitus, tobacco smoking, spinal anesthesia, and preoperative anemia were independent predictors for prolonged LOS (p<0.05 for all). For the endpoint of non-home discharge, LOS = 2 days (OR: 14, 95% CI: 11-19, p<0.01), age =80 years (OR: 7.6, 95% CI: 4.8-12.3, p<0.01), and functional dependency (OR: 5.8, 95% CI: 3.5-9.6, p<0.01) were the strongest predictors (Fig 2). Additionally, female sex, age =60 years, obesity, diabetes mellitus, general anesthesia, operative time >90 mins, and preoperative anemia were independent predictors of non-home discharge after UKA (p<0.05 for all).

Conclusion

UKA can be safely performed as an outpatient surgery or with a limited single night stay in the hospital. However, this study identified that 40% of patients that underwent UKA required at least 2 days of inpatient care. This study identified multiple predicators of prolonged LOS with preoperative functional dependency, older age and increased operative time being the biggest risk factors. As more surgeon’s transition to outpatient UKA and ambulatory surgery settings, these risk factors should be considered when indicating patients for outpatient UKA.