Steep cup abduction angles with adverse joint loading may increase traditional polyethylene bearing wear in total hip arthroplasties. However, there have been few reports evaluating the effect of cup inclination on the wear of dual-mobility devices. In a hip joint simulation, we compared the short-term wear of two-sizes of modular highly cross-linked dual-mobility bearings (28 mm femoral head diameter/42 mm polyethylene insert outer diameter/54 mm acetabular shell diameter; 22.2 mm femoral head diameter/ 36 mm polyethylene insert outer diameter/48 mm acetabular shell diameter) at 50 and 65˚of cup inclination with modular 28 mm femoral head on 54 mm cup diameter metal-on-highly cross-linked polyethylene bearings. Increasing inclination from 50-65˚had no changes in volumetric wear of 28/42/54 mm (mean, 1.7 vs. 1.2 mm 3 /million cycles, respectively; p ¼ 0.50) and 22.2/36/48 mm (mean, 1.7 vs. 1.2 mm 3 /million cycles, respectively; p ¼ 0.48) dual mobility bearings. At 65˚, 22.2/36/48 mm dual-mobility bearings had lower volumetric loss (mean, 2.2 vs. 6.3 mm 3 ; p ¼ 0.03) and wear rates (mean, 1.2 vs. 2.7 mm 3 /million cycles; p ¼ 0.02) compared to metal-onhighly cross-linked polyethylene bearings. Modern-generation dual-mobility designs with highly cross-linked polyethylenes may potentially withstand edge-loading from steeper cup-inclinations without substantial decreases in wear. ß
Static, three-dimensional computerized simulation studies suggest differences that may influence the risk of dislocation among components with varying geometries, favoring anatomic and modular dual-mobility designs. Clinical studies are needed to confirm these observations.
Our results indicate that the jumbo cup technique results in hip center elevation despite placement of the cup adjacent to the inferior acetabulum. For a hypothetical increase from a 54-mm socket to a 72-mm socket, as one might see in the context of the revision of a failed THA, our model would predict an elevation of the hip center of approximately 5 mm and loss of approximately 15 mm of anterior column bone. This suggests that an increase in femoral head length may be needed to compensate for the hip center elevation caused by the use of a large jumbo cup in revision THA. A jumbo cup may also result in protrusion through the anterior wall.
Background Dislocation remains common after total hip arthroplasty. Efforts have been made to identify and minimize risk factors. One such factor, jump distance, or the distance the femoral head must travel before dislocating, has been poorly characterized with respect to threedimensional kinematics.Questions/purposes We therefore determined: (1) the three-dimensional stability of four different component designs; (2) whether the degree of abduction and anteversion affects the stability; (3) whether pelvic inclination angles affected stability; and (4) which combination of these three factors had the greatest stability. Methods We created a positionable three-dimensional model of a THA. Acetabular components were modeled in various abduction and anteversion angles and in two different pelvic inclinations which simulate standing and chair-rising activities.
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