Impact of obesity on outcomes after total hip and knee replacement: A study on hospital length of stay and readmission rates in NHS Scotland

Introduction

Obesity presents significant challenges in the perioperative management of patients undergoing total hip replacement (THR) and total knee replacement (TKR). This study investigates the association between BMI and the outcome measures length of stay and 30-day readmission rate, among National Health Service (NHS) patients in Scotland.

Methods

This analysis included data from 50,751 patients who underwent THR or TKR between July 2019 and February 2025. BMI was categorised into six groups then further divided into two categories: “Not Obese” and “Obese”. LOS was classified as short or long. The analysis included a statistical method to visualise the relationship between BMI and the outcomes and logistic regression models that incorporated additional factors to assess their association with the outcomes.

Results

Patients with a BMI ≥40 had a longer mean length of stay (LOS) of 3.44 days and a median of 3 days, compared to a mean of 3.02 days and a median of 2 days among those with BMI <40 (p < 0.001). The odds of experiencing a prolonged hospital stay increased progressively with BMI thresholds: odds ratios were 1.43 for BMI ≥40, 1.53 for BMI ≥45, and 1.89 for BMI ≥50 (all p < 0.001). Patients with higher BMI, particularly those classified as Super Obese, demonstrated elevated 30-day readmission rates, reaching up to 17.5 %.

Conclusion

Higher BMI, especially in the morbidly and super obese ranges, is associated with extended hospital stays and increased 30-day readmission rates following THR and TKR.