The Role of Body Mass Index in Perioperative Complications Among Patients Undergoing Total Hip Arthroplasty

Introduction: Osteoarthritis is a degenerative joint disease characterized by the breakdown of cartilage and underlying bone, often resulting in significant pain and disability, particularly in weight-bearing joints such as the hips, knees and spine. Obesity is a wellestablished risk factor for osteoarthritis, as it increases mechanical stress on the joints and contributes to systemic inflammation. While total hip arthroplasty (THA) is an effective treatment for end-stage osteoarthritis, the impact of body mass index (BMI) on perioperative and postoperative outcomes remains a topic of debate, with some studies suggesting increased complications in obese patients, with other studies reporting no significant difference. This variability highlights the need for more research in understanding this relationship. This paper aims to evaluate the effect of BMI on perioperative outcomes in THA. Methods: A retrospective cohort study of the TriNetX US Collaborative Network, an electronic health record repository of United States healthcare organizations including over 117 million patients, was conducted. Current Procedural Terminology codes were used to identify a cohort of patients who received THA between January 1, 2020 and January 1, 2025. Patients were stratified into five BMI categories: underweight (< 18.5 kg/m2 ), normal (18.5–24.9 kg/m2 ), overweight (25–29.9 kg/m2 ), Obesity Class I (30–34.9 kg/m2 ), Obesity Class II (35 - 39.9 kg/m2 ) and Obesity Class III (> 40 kg/m2 ). Outcomes were compared between each BMI group to normal weight and post-operative outcomes and BMI were evaluated for clinical significance. Cohorts underwent 1:1 propensity score matching based on sex, BMI, and medical comorbidities. Postoperative medical and surgical complications were assessed between 0-30 days. Differences between groups were assessed by Student’s t-test. Odds ratios (OR) were calculated. Significance was defined as p < 0.05. Postoperative outcomes examined in this study included: acute myocardial infarction, acute kidney failure, pneumonia, acute embolism, anemia, sepsis, pulmonary embolism and cerebral infarction. Results: During the study period 110,282 patients underwent a total hip arthroplasty. After 1:1 propensity score matching, patients with Class II to were less likely to develop acute kidney failure (5.2% vs 7.8%, OR 0.641, p= 0.000) and more likely to develop cerebral infarction (16.1% vs 59.26%, OR 3.089, p = 0.000) and anemia (10.6% vs 13.56%, OR 1.203, p= 0.003). For Class III obesity, there was a statistically significant difference in developing acute kidney failure (3.3% vs 5.6%, OR 0.436, p=0.025) and acute embolism (4.3% vs 9.8%, OR 0.645, p=0.037). Discussion/Conclusion: Our study focuses on total hip arthroplasty in osteoarthritis and the relationship between a patient’s BMI and postoperative outcome. Obesity is known to be associated with increased surgical risks; our study indicates a nuanced relationship between BMI and specific postoperative outcomes. We found higher BMI categories demonstrated a lower incidence of acute kidney failure but had a greater likelihood of anemia and cerebral infarction. Limitations of the study included the inability to perform a multivariate analysis with the data set. Further research is needed to develop preoperative management strategies and guidelines to reduce patient morbidity.