Are Morbidly Obese Patients Undergoing Total Hip Arthroplasty at an Increased Risk For Component Malpositioning?

Acetabular cup positioning is a critical factor in determining adverse clinical outcomes in THA. This evaluation was performed to determine if morbid obesity (BMI ≥35 kg/m²) is a contributing risk factor to cup malpositioning. Two groups of patients were obtained from a local arthroplasty registry and match-controlled for gender, age, and diagnosis (n = 211 morbidly obese; n = 211 normal). Intraoperative data and postoperative AP pelvis and cross-table lateral radiographs were obtained for each patient. The Martell Hip Analysis Suite was used to calculate cup positioning (successful positioning defined as 30°–45° of abduction, and 5°–25° of anteversion), as well as varus–valgus alignment of the femoral stem. There was a significant correlation between morbid obesity with respect to underanteversion; using multivariate analysis, there was a trend toward a combined underanteversion/overabduction of the acetabular cup. Of all variables considered, high BMI was the most significant risk factor leading to malpositioning.