Polyethylene wear of dual mobility cups: a comparative analysis based on patient-specific finite element modeling

Abstract

Purpose: Concerns remain about potential increased wear with dual mobility cups related to the multiple articulations involved in this specific design of implant. 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 was developed for 15 patients undergoing primary total hip arthroplasty (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). However, 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.

Conclusion: When using XLPE instead of UHMWPE, dual mobility cup with a 22.2-mm-diameter femoral head produced a similar amount of volumetric wear than conventional acetabular component with a 32-mm-diameter femoral head against XLPE. Therefore, XLPE is advocated in dual mobility cup to improve its wear performance.

Keywords: Dual mobility cup; Highly cross-linked polyethylene; Patient-specific modeling; Polyethylene mobile component; Polyethylene wear.

Fig. 1

Workflow of the patient-specific modeling using patient’s hip anatomy, weight and height to predict joint reaction force (JRF) and joint angle (JA), which were used as boundary conditions of the finite element models of dual mobility (DM22PE and DM22XL) and conventional (SD22PE, SD32PE and SD32XL) cup constructs to evaluate polyethylene wear

Fig. 2

Hip angles and joint reaction force during the walking cycle. The gray area represents the minimum and maximum values over the 15 patients

Fig. 3

Volumetric (A) and linear (B) wear rates of polyethylene components for dual mobility cup with a 22.2-mm-diameter femoral head against UHMWPE (DM22PE), conventional cup with a 22.2-mm-diameter femoral head against UHMWPE (SD22PE), conventional cup with a 32-mm-diameter femoral head against UHMWPE (SD32PE), conventional cup with a 32-mm-diameter femoral head against highly cross-linked PE (SD32XL) and dual mobility cup with a 22.2-mm-diameter femoral head against highly cross-linked PE (DM22XL). The boxplots show quartiles and mean (circle)

Fig. 4

Volumetric wear of SD22PE, SD32PE and DM22XL (y-axis) compared to DM22PE (x-axis) for the 15 simulated patients

Fig. 5

Wear repartition onto the concave inner (A) and convex outer (B) bearing surfaces of the polyethylene mobile component (DM22PE). Note: the color scales are different

Fig. 6

Correlations between the volumetric wear of DM22PE and DM22XL and maximum joint reaction force (A) and BMI (B) for the 15 simulated patients (gray area represent 95% CI)