The Burden of Weight on Joint Replacement: A 1.6 Million-Patient Analysis of BMI and Hip Arthroplasty Outcomes

Background: THA is a gold-standard intervention for end-stage hip osteoarthritis, historically performed in older adults. However, the growing global obesity epidemic is reshaping this landscape. Emerging evidence suggests that elevated body mass index (BMI) may not only worsen perioperative outcomes but also accelerate the need for surgery at a younger age. Understanding how BMI influences both the timing and safety of THA is crucial to optimizing care in this evolving patient population. Methods: We conducted a retrospective analysis of 1,626,965 elective THA hospitalizations from the Nationwide Inpatient Sample. Patients were stratified by BMI into three categories: <29.9, 30–34.9, and ≥35. Fracture- and oncology-related cases were excluded. ICD-10 codes identified comorbidities and complications. Primary outcomes included age at surgery, in-hospital mortality, length of stay (LOS), complications, and hospitalization costs. Statistical analysis used Pearson correlation, linear regression, chi-square tests, and t-tests via SPSS version 26.0.0.0. Results: Higher BMI was significantly associated with younger age at THA (r = −0.187, p < 0.001). Each 5-unit BMI increase corresponded to a ~2-year decrease in age at surgery. Obese patients had higher rates of hypertension, diabetes, dyslipidemia, and sleep apnea. Complications including blood loss anemia, acute kidney injury, venous thromboembolism, and postoperative infections were more common in higher BMI groups. LOS increased with BMI, though total hospital charges showed minimal clinical variation. Conclusions: Obesity is a key driver of earlier THA and elevated perioperative risk. These findings underscore the need for BMI-tailored surgical planning and risk stratification. As younger, high-BMI patients increasingly undergo THA, future strategies must focus on preoperative optimization, complication prevention, and long-term implant durability.