Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science




Vasarhelyi, Edward


The demand for revision total knee arthroplasty (RTKA) is increasing due to obesity and an aging population. The purpose of this study is to evaluate the effect of different body mass index (BMI) categories on RTKA using a retrospective cohort analysis. The first part was to assess patients’ functionality post-RTKA. The second part was to determine the survival of RTKA and re-revision rate. The third part was to explore the complication and readmission rates, and to estimate the 90-day costs of RTKA. We found the most common indication for RTKA in super obese patients is infection, unlike other BMI categories, whose most common indication is aseptic loosening. The improvement after RTKA is comparable across all BMI cohorts. Our analysis showed that a BMI ≥45 kg/m2 increases the risk of infection and re-revision, but only super obese patients are at an increased risk of readmissions and therefore have higher 90-day costs.

Summary for Lay Audience

The prevalence of obesity is increasing worldwide. Its hazardous effect on people’s health has led to investigations of its impact on arthroplasty. The literature documents an increased complication rate of primary and revision total knee arthroplasty (RTKA) due to obesity, which consequently has caused many surgeons to avoid operating on patients whose body mass index (BMI) is above a certain threshold, in order to avoid harming their and the hospitals’ reputation. Therefore, many patients are prohibited from the benefits of RTKA due to perceived higher risks and costs based on an arbitrary threshold. This study investigates the effect of obesity on RTKA by classifying it into several categories and looking into its influence on gain in quality of life (QoL), RTKA survival, complication rate, re-revision rate, readmission rate and costs within 90 days of operation. The six weight categories used in the study are in an ascending manner: normal weight, overweight, obesity, severe obesity, morbid obesity and super obesity. It was found that RTKA improves QoL similarly across all BMI classes. Morbid and super obese patients, however, present at a younger age for RTKA, are at an increased risk of postoperative infection and the survival of their RTKA is less, necessitating more re-revision. Super obese patients are also at an increased risk for readmission, which in turn boosts their total 90-day costs by 25%. Thus, only patients whose BMI is ≥45 kg/m2 are at increased risk of complications and may need further evaluation prior to RTKA, while those below this threshold must be operated on for the benefits of RTKA and the similar risk profile to patients with normal weight.

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