Predictors of extended length of stay after unicompartmental knee arthroplasty

To identify factors that independently predict extended length of stay after unicompartmental knee arthroplasty (UKA) surgery (defined as length of stay longer than 3 days), and to identify factors predicting early post-operative complications.

A retrospective analysis of all patients undergoing UKA from January 2016-January 2019 at our institution was performed. Clinical notes were reviewed to determine the following information: Patient age (years), gender, American Society of Anesthesiologists (ASA) grade, weight (kg), height (meters), body mass index (BMI), co-morbidities, indication for surgery, surgeon, surgical volume, surgical technique (navigated or patient-specific instrumentation), implant manufacturer, estimated blood loss (ml), application of tourniquet during the surgery, application of drain, hospital length of stay (days) and surgical complications.

Multivariate regression analysis showed that ASA 3-4 vs. ASA 1-2 [OR 4.4 (CI; 1.8-10.8, p = 0.001)] and a history of cardiovascular disease [OR 2.8 (CI; 1.4-5.5), p = 0.004)] were significant independent predictors of prolonged length of stay. Hosmer-Lemeshow goodness of fit of the model showed a p-value of 0.214. Nagelkerke R-Square was 0.2. For complications, multivariate regression analysis showed that ASA 3-4 vs. ASA 1-2 [OR 5.8 (CI; 1.7-20.7)] and high BMI (BMI >30) [OR 4.3 (CI; 1.1-17.1)] were significant independent predictors of complications. Hosmer-Lemeshow goodness of fit was 0.89 and Nagelkerke R-Square was 0.2. Patients treated with robotics (Navio) techniques had shorter length of stay median 51 h (IQR; 29-96) when compared to other techniques 72 h (IQR; 52-96), p = 0.008.

Based on the results of our study, high ASA grade (≥3) appears to be the most important factor excluding eligibility for fast-track UKA. Any number of co-morbidities may increase ASA, but in and of themselves, apart from a history of cardiovascular disease, they should not be seen as contraindications. Appropriate patient selection, technical tools and details during the surgery could facilitate fast track surgery.