# Impact of obesity on early in-hospital postoperative outcomes following total knee arthroplasty in older adults: a comparative study of class I and class II obesity

## TL;DR

This study compares postoperative outcomes in older adults with Class I and Class II obesity after total knee arthroplasty, finding higher risks for Class II patients.

## Contribution

The study provides new evidence on the differential impact of Class I and Class II obesity on early postoperative outcomes following TKA in older adults.

## Key findings

- Class II obesity is associated with higher in-hospital mortality and complications like acute kidney injury and pneumonia.
- Class II obesity patients had a 3.3% lower risk of blood loss anemia compared to Class I patients.
- No significant differences were found in several other complications like heart failure or pulmonary embolism.

## Abstract

The rising prevalence of obesity has increased the demand for total knee arthroplasty (TKA), but the impact on outcomes, particularly in Class I and II obesity, remains inconclusive. This study aimed to compare early in-hospital post-TKA outcomes in older patients with Class I (BMI 30–34.9 kg/m²) and Class II obesity (BMI 35–39.9 kg/m²).

Using data from the Nationwide Inpatient Sample (2016–2019), patients aged 65 and above who underwent TKA were categorized into Class I (n = 133,425) and Class II obesity groups (n = 122,432). Propensity score matching balanced baseline characteristics. Primary outcomes included in-hospital mortality and early postoperative complications.

Post-matching, a higher prevalence of type 2 diabetes was found in the Class II obesity group (32.5% vs. 29.5%, P = 0.001). The Class II group had a significantly higher risk of in-hospital mortality (9.004-fold, 95% CI: 3.57–22.68, P < 0.001), acute kidney injury (45.8% increase, 95% CI: 1.383–1.537, P < 0.001), and postoperative pneumonia (32.5% increase, 95% CI: 1.095–1.604, P = 0.004). The risk of blood loss anemia was 3.3% lower in the Class II group (95% CI: 0.946–0.988, P = 0.002). No significant differences were found in heart failure, acute coronary artery disease, pulmonary edema, venous thromboembolism, pulmonary embolism, and blood transfusion.

More intensive monitoring and preventive measures may be necessary for patients with Class II obesity to mitigate the heightened risks associated with TKA compared to those with Class I obesity.

The online version contains supplementary material available at 10.1007/s00402-025-05763-6.