Abstract
Introduction
Polyethylene (PE) wear is clearly linked to total hip arthroplasty (THA) failure, leading to osteolysis and decreasing survivorship rates. Dual mobility cups (DMC) are widely used to prevent or treat THA instability. However some studies have pointed PE wear risk as a “dual wear” risk. Hip wear simulation is usually used to understand factors influencing wear and to differentiate design, PE types and materials performances. To date, few works have been published studying dual mobility insert wear.
Objectives
Our objective was to evaluate wear of DMC with comparison with a fixed single articulating hip design and to measure wear under same conditions (loading cycle, temperature, sterilization, material and surface roughness).
Methods
The test bench includes one station for a control sample and one for dynamic test. Those are driven independently one from the other. Two electrical actuators applied the forces and two forces sensors putted on the fixing plate of the acetabular part gave the corresponding values. On the dynamic station, the angular movements are generated by an electric motor. Sleeves are installed on the bowls containing the testing liquid and on the supports of acetabular parts, in order to get a tight volume that excludes contaminant particles. Wear is measured by a gravimetric method. The simulator is stopped and implants have been removed from the simulators in order to achieve weighting and observations at 0.5, 1, 2, 3, 4 and 5 millions cycles. At the end, the sample PE insert and the control one are removed from their cup in the aim to measure the mass loss.
Results
Under same conditions the gravimetric wear and the linear penetration of the head are perfectly comparable between a conventional and a dual mobility cup.
Conclusion
In vitro, DMC wear is equal or less important than a standard single fixed cup and volumetric wear is lower than published data. Wear of the two joints of a DMC is not increased thanks to the recruitment phenomenon and the freedom induced by the concept.
