Primary Total Hip Arthroplasty in Patients Who Have Morbid Obesity: A Propensity-Weighted Analysis of Dual Mobility and Standard Fixed-Bearing Implants.

Abstract

Dual mobility (DM) bearings in total hip arthroplasty (THA) are designed to offer enhanced stability compared to traditional fixed-bearing constructs. However, the stability and durability of DM implants subjected to increased forces in the setting of morbid obesity remain underexplored. This study aimed to compare outcomes of DM and fixed-bearing constructs among morbidly obese patients following primary THA. We retrospectively reviewed patients who had a body mass index (BMI) greater than 40 and underwent primary THA between 2005 and 2022 using an institutional total joint registry. Those who had less than two years of follow-up and fixed-bearing head sizes less than 36 mm were excluded. There were 69 patients who received DM and 943 who received fixed-bearing implants that were included, achieving a mean follow-up of 6.0 years (range, 2.0 to 17.2). Dual mobility patients were older (mean age 63.0 versus 60.8 years, P = 0.032), more commonly women (73.9 versus 43.6%, P < 0.001), had higher BMI (mean 45.5 versus 44.5, P = 0.019), and more frequently underwent posterior approach THA (91.3 versus 59.9%, P < 0.001). Using propensity weighting to adjust for age, sex, BMI, surgical approach, surgical indication, spine disease, and spine surgery, Kaplan-Meier analyses assessed survivorship free from instability, revision, reoperation, and nonoperative complication. Rates of instability were low in both DM and fixed-bearing groups (1.4 versus 0.6%). There were no revisions that occurred following DM THA, whereas 43 fixed-bearing constructs required revision (0 versus 4.6%, P = 0.070), including five (0.5%) for instability. Reoperation (1.4 versus 7.1%; P = 0.070) and nonoperative complication (5.8 versus 5.5%; P = 0.921) rates were similar. Propensity-weighted five-year survivorship free from instability, revision, reoperation, and nonoperative complication was 98.6, 100.0, 98.5, and 94.2% for DM and 99.4, 96.8, 94.1, and 92.3% for fixed-bearing implants. In morbidly obese patients, DM implants demonstrated excellent five-year survivorship with outcomes comparable or slightly superior to fixed-bearing constructs. These findings suggest DM implants may provide stability without increasing complication rates in this high-risk population.