J Wegrzyn, A Antoniadis, E Sarshari, M Boubat, A Terrier
(Lausanne, Suisse)
Introduction:
Although dual mobility cups demonstrate a marked increase in use to achieve stability during primary and revision total hip arthroplasty (THA), concerns remain about potential increased wear related to the multiple articulations involved in this specific design of implant. Therefore, a better understanding, quantification and prediction of wear with dual mobility cup is needed. This finite element analysis study aimed to compare polyethylene (PE) wear between dual mobility cup and conventional acetabular component, and between the use of conventional ultra-high molecular weight PE (UHMWPE) and highly cross-linked PE (XPLE).
Methods:
Patient-specific finite element modeling were developed for 15 patients undergoing primary THA. Five acetabular components were 3D modeled and compared in THA constructs replicating existing implants: a dual mobility cup with a 22.2 mm diameter femoral head against UHMWPE or XLPE (DM22PE or DM22XL), a conventional cup with a 22.2 mm diameter femoral head against UHMWPE (SD22PE), and a conventional cup with a 32 mm diameter femoral head against UHMWPE or XLPE (SD32PE or SD32XL).
Results:
DM22PE produced 4.6 times and 5.1 times more volumetric wear than SD32XL and DM22XL (p<0.0001, Cohen’s d=6.97 and 7.11; respectively). Even if significant, the differences in volumetric wear between DM22XL and SD32XL as well as between DM22PE and SD22PE or SD32PE were small according to their effect size (p<0.0001, Cohen’s |d|=0.48 to 0.65), and could be therefore considered as clinically negligible. Regarding the wear repartition during the simulated walking cycle, the ratio of volumetric wear of the convex outer bearing surface by the concave inner bearing surface was 1/187 for DM22PE and 1/353 for DM22XL.
Conclusion & perspectives:
This numerical study demonstrated that, when using XLPE instead of UHMWPE, a dual mobility cup with a 22.2 mm diameter femoral head produced a similar amount of volumetric wear than a conventional cup with a 32 mm diameter femoral head against XLPE. For both DM22PE and DM22XL, motion and volumetric wear predominated at the small articulation during level walking gait. Therefore, the convex outer bearing surface of PE mobile component did not represent a significant source of wear in dual mobility cup. In conclusion, the use of XLPE is advocated in dual mobility cup to improve its wear performance especially in young, active and high functional demand patients.