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

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.