Influence of Acetabular Shell Position and Component Design on Hip Dynamic Dislocation

Dislocation is a major complication following total hip arthroplasty, with risk factors such as surgical technique, implant positioning, and implant design. Literature has suggested the distance the femoral head must travel before dislocation to be a predictive factor of dislocation where smaller travel distance has increased dislocation risk. The purpose of this study was to compare 3 designs (hemispherical, metal-on-metal, and dual mobility [DM]) in terms of the dynamic dislocation distance and force required to dislocate.

This dynamic dislocation distance model used a material testing system that defined acetabular component inclination (30°, 45°, and 60°), anteversion angles (0°, 15°, and 30°), and pelvic tilt (5° [standing] and 26° [chair rise]). Testing groups included a hemispherical shell with a modular polyethylene liner and 32-mm head, a metal-on-metal hip resurfacing cup design with a 40-mm CoCr head, and a DM design with a 42-mm outside diameter articulating liner and an inner 28-mm articulating head.

The dynamic dislocation distance of the DM hip was greater than that of the other designs for all inclination, anteversion, and pelvic tilt angles tested with the exception of 60° inclination/0° anteversion. At 26° pelvic tilt, it was observed that dislocation distance increased with greater anteversion and decreased with larger inclination.

Clinical results have shown the DM design may reduce dislocation. These data support those findings and suggest that if instability is a concern preoperatively or intraoperatively, using a DM implant increases the dynamic dislocation distance.