The influence of Obesity on outcomes following Total Knee Arthroplasty

Abstract

With the rising obesity and the increasing age of the population, a large proportion of patients who undergo Total Knee Arthroplasty (TKA) are obese. Knowing the health risks associated with obesity, it is important to determine if the outcomes of a TKA is compromised in obese patients. Significant discrepancies in the findings of previous studies assessing the effect of body mass index (BMI) on TKA outcomes were observed in a literature review, thus making it difficult to confirm an effect of obesity measured as BMI on the outcomes after TKA. This thesis comprises two studies which further explored the effects of BMI and other body composition measures on the outcome of TKA. 1. The aim of a retrospective epidemiological study was to assess the effect of BMI on patient reported outcomes after TKA. 2. The aim of the prospective cohort study was to assess the effect of body composition, measured by waist circumference (WC), waist to hip ratio (WHR), bioelectrical impedance analysis (BIA), ultrasonography (US) and BMI, on patient reported outcomes after TKA. It was concluded from these two studies that group division of obesity based on the classification of BMI greater or less than 30 kg/m2 could not identify an effect of obesity on outcomes. However, on using BMI as a continuous variable, an adverse effect of BMI on knee function and overall physical health was evident for higher BMI ranges. Body composition measures of BIA and US did not detect an effect of obesity for any outcomes. Effect of obesity detected by BMI and WC was similar. The negative association of BMI and outcomes observed was very weak across BMI ranges of 25-30 kg/m2and a significant association was achieved due to poorer patient reported physical function (indicated by Short Form 12 and Oxford Knee Score questionnaires) in some cases with very high BMI values (> 40 kg/m2). In addition to this finding, the lack of group difference when outcomes were evaluated across a BMI of 30 kg/m2in the two studies and the disparity between studies in the results when using a BMI classification of 30 kg/m2 supported the conclusion that a BMI classification across a cut-off value of 30 kg/m2 does not predict a poor result in obese after TKA. However, because of the limited number of highly obese (> 35kg/m2) participants in both studies of the thesis and often in previous studies, no definite conclusions regarding the effect of higher obesity levels on the outcome of TKR can be drawn from the studies in this thesis. Adequately powered future studies with more morbidly obese participants could give more definitive answers to the effect of BMI and other measures of body composition on outcomes following TKA.