The effect of acetabular shell and liner design on posterior horizontal dislocation distance in modern dual-mobility implants.

Abstract

The posterior horizontal dislocation distance (PHDD) is a 3-dimensional jump distance measurement that is relevant to the risk of dislocation. There are a number of dual-mobility (DM) constructs with varying designs available. The present study identifies design factors associated with increased PHDD and evaluates the PHDD of 3 DM implants. 3 different computer-aided implant designs were virtually implanted within a 3-dimensional CT-derived pelvic model. Each design represented an analogue of a DM system (MDM, OR3O, and G7) according to specific variations in acetabular liner rim build-up and femoral head centre location. The effective head diameters and PHDD values were calculated for each size acetabular shell and DM design. The positive rim build-up design (MDM) showed higher PHDD values as compared to the other 2 hemispherical rim designs with no build-up, across all studied shell sizes. Specifically, the MDM design analogue had 16.4-29.0% greater PHDD values than the OR3O design analog and 15.2-30.5% greater PHDD values than the G7 design analogue The effect of a sfemoral head centre location relative to the liner head centre (OR3O) was negated by a larger effective head diameter to shell diameter ratio of the G7 design, resulting in similar PHDD values. Design parameters affect the PHDD values of DM cups. The use of an elevated rim was associated with greater PHDD values. A medialised femoral head centre should also improve PHDD values, but the effect was nullified due to consecutive lower effective head diameters.