Contemporary Dual Mobility Head Penetration at Five Years: Concern for the Additional Convex Bearing Surface?

Background: Dual mobility (DM) bearings are increasingly popular and second-generation designs contain highly cross-linked polyethylene. The purpose of this study is to report head penetration rates in modern DM bearings. Methods: A review of 63 consecutive DM bearings was performed. Radiographs were analyzed for head penetration using Martell methodology at regular postoperative intervals. Results: Thirty-four DM bearings were analyzed. Mean linear head penetration was 1.59 mm/y at 1 year, 1.07 mm/y at 2 years, and 0.27 mm/y at 5 years following an exponential regression model (R ² = 0.999). Mean volumetric wear was 783 mm ³ /y at 1 year, 555 mm ³ /y at 2 years, and 104 mm ³ /y at 5 years following an exponential regression model (R ² = 0.986). Conclusion: Initial head penetration of DM bearings is larger than contemporary cross-linked polyethylene bearings; however, rates approach steady state after 2 years, analogous to traditional bearings. The larger “bedding-in” head penetration may be due to the additional convex bearing surface, creating 2 surfaces for deformation/wear.