Morbid Obesity May be Associated With Increased Odds of Prosthetic Joint Infection After Anterior-Based Total Hip Arthroplasty

Background Obesity increases perioperative risk after total hip arthroplasty (THA), particularly with anterior-based approaches. However, outcomes among patients with class II versus class III obesity remain poorly defined. This study compared early complications and patient-reported outcomes (PROMs) between these obesity classes. Methods We retrospectively reviewed patients with BMI ≥35 kg/m² undergoing elective anterior-based primary THA from January 2022 to January 2025. Patients were stratified into BMI 35-39.9 kg/m² (Class II) and BMI ≥40 kg/m² (Class III) cohorts. Firth penalized logistic regression evaluated the association between BMI group and prosthetic joint infection (PJI) requiring operative irrigation and debridement (I&D). Results 193 patients were included (BMI ≥40: n=53; BMI 35–39.9: n=140). The BMI ≥40 kg/m² cohort had a greater proportion of females (77.4% vs 57.1%; P = .015) and higher ASA classification ( P = .02). PJI occurred more frequently in the BMI ≥40 cohort (7.5% vs 1.4%; P = .049). Unadjusted odds of PJI were higher with BMI ≥40 kg/m² (OR 5.03, 95% CI 1.08-29.6), but the association was no longer statistically significant after adjustment for age, sex, and surgical approach. Both cohorts demonstrated significant improvement in WOMAC and SF-12 Physical scores at 3 months without between-group differences. Conclusions Patients with BMI ≥40 kg/m² demonstrated higher observed PJI rates after anterior-based THA while achieving comparable early functional improvement. These findings suggest a clinically important risk signal warranting confirmation in larger studies rather than establishing BMI ≥40 kg/m² as an independent risk threshold.