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

Abstract

BackgroundDual 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. MethodsA review of 63 consecutive DM bearings was performed. Radiographs were analyzed for head penetration using Martell methodology at regular postoperative intervals. ResultsThirty-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 (R2 = 0.999). Mean volumetric wear was 783 mm3/y at 1 year, 555 mm3/y at 2 years, and 104 mm3/y at 5 years following an exponential regression model (R2 = 0.986). ConclusionInitial 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.