Obesity continues to be more prevalent in the United States, which contributes to the risk of developing osteoarthritis that leads to an increased demand for THA. Obesity rates are also steadily increasing, and, by 2030, are expected to exceed 50% . Previous literature has shown an increase in obesity rates over time for patients undergoing THA, and that THA patients have a significantly higher average BMI compared to the overall United States population . Additionally, patients with obesity may require THA at a younger age and are at a higher risk for perioperative complications after THA, including infection, wound complications, and aseptic loosening, which are more profound for THA vs. TKA [10,11,12,13]. Despite lower objective outcomes, obese patients are shown to benefit significantly from THA, as large studies demonstrated significant improvement after THA for all weight classes [14, 15]. Thus, more evidence is needed to evaluate protocols around THA in patients with obesity. The introduction of value-based payments in the most recent decade has shown an increased focus on such protocols like weight optimization and weight assessment for THA patients. Therefore, the goal of this study was to investigate change in obesity rates from 2013–2020 for patients receiving THA at a large urban academic health system relative to a population receiving annual physicals at the same institution. Our findings suggest that while THA patients are significantly more obese than the general population of patients, there have been stable trends in BMI and obesity rates over time among these patients compared to increasing trends seen in our general population.
Prior research has shown increasing prevalence of obesity in the United States, and that those who receive THA have higher BMI than the average American [5, 9]. Our findings corroborated this finding. Average BMI for the general patient population at our institution has steadily increased over the last decade. Those who received THA had higher average BMI than the APG group in every year studied. However, while prior studies have shown increase, over time, of average BMI for THA patients , our analysis showed that in the last eight years, there has been no significant positive or negative trend in obesity rates for our patients who undergo THA. In 2013, our institution was one of the first to enter into a value-based care contract through BPCI. These programs penalize institutions for poor outcomes and encourage preoperative optimization of modifiable risk factors like obesity. While there is substantial evidence for increased complications and worse outcomes for THA in patients with morbid obesity, studies have also shown that these patients benefit significantly from THA [17,18,19]. In this study period, our THA patients did not show the upward trend in prevalence of obesity demonstrated by historical data and our own general patient population over the same period. Although the average BMI among our THA was greater than the APG cohort at all-time points. Further study of the effects of optimization and future direction for THA in patients with obesity may be warranted.
A more granular analysis separating patients in to underweight, normal weight, Class I obesity, Class II obesity, and Class III obesity found proportion of THA patients in all five weight classes was stable during the study period. Conversely, the APG cohort had progressively higher proportions of patients in all obese classifications, and lower proportions of patients in the underweight category. Previous literature has shown that Class III obese THA patients have longer LOS and higher readmission and major complication rates than patients without obesity [20, 21]. A study by Fu et al. investigating THA in patients with obesity found that malnutrition is more prevalent in patients with Class III obesity than in Class I obesity, and portends worse outcomes than obesity itself . Katakam et al. analyzed 1256 THAs and found that obesity Class III patients were 2.5 times more likely not to achieve minimal clinically relevant improvement in patient-reported outcome measures after surgery . As a result, hospitals and surgeons will need to enhance optimization and patient selection for THA.
While previous literature has clearly linked obesity to worse outcomes and increased risk of complications after THA, there is less consensus regarding outcomes for underweight THA patients. Studies have shown that underweight patients who undergo primary THA require longer LOS and are readmitted more often than patients in normal weight categories, but they do not have higher rates of complications [24,25,26]. Possible explanations for these findings include prevalence of malnutrition among underweight patients . Studies have also shown a relatively low rate of THA in patients who are underweight . Our findings concurred with this result, as underweight patients were the only weight category studied where proportions were consistently lower for the THA cohort than for the APG cohort over the study period.
As a retrospective study extracted from electronic medical records, our data are limited, depending on accurate documentation such as ICD coding of physical exams and THA. Additionally, specifically selecting patients who have received an annual physical exam at our healthcare network to represent the general public may be biased towards those with more health access or may not account for those seeking care for a wide range of reasons, which could have influenced the lower obesity rates observed in our APG. The generalizability of our data is further limited due to the regional differences in obesity trends observed as the levels of obesity in our metropolitan urban area may differ from other areas of the country with higher or lower levels. Finally, the BMI of the general public may not be reflected in patients who self-select to undergo annual physical examinations. Despite these limitations, our observational study used sound design and statistical methodology, which, combined with access to a comprehensive patient record database, allows us to be confident in the reliability and validity of our data.