May the surface roughness of the retrieved femoral head influence the wear behavior of the polyethylene liner?

Wear testing of a canine hip resurfacing implant that uses highly cross-linked polyethylene

Hip resurfacing offers advantages for young, active patients afflicted with hip osteoarthritis and may also be a beneficial treatment for adult canines. Conventional hip resurfacing uses metal-on-metal bearings to preserve bone stock, but it may be feasible to use metal-on-polyethylene bearings to reduce metal wear debris while still preserving bone. This study characterized the short-term wear behavior of a novel hip resurfacing implant for canines that uses a 1.5 mm thick liner of highly cross-linked polyethylene in the acetabular component. This implant was tested in an orbital bearing machine that simulated canine gait for 1.1 million cycles. Wear of the liner was evaluated using gravimetric analysis and by measuring wear depth with an optical scanner. The liners had a steady-state mass wear rate of 0.99 ± 0.17 mg per million cycles and an average wear depth in the central liner region of 0.028 mm. No liners, shells, or femoral heads had any catastrophic failure due to yielding or fracture. These results suggest that the thin liners will not prematurely crack after implantation in canines. This is the first hip resurfacing device developed for canines, and this study is the first to characterize the in vitro wear of highly cross-linked polyethylene liners in a hip resurfacing implant. The canine implant developed in this study may be an attractive treatment option for canines afflicted with hip osteoarthritis, and since canines are the preferred animal model for human hip replacement, this implant can support the development of metal-on-polyethylene hip resurfacing technology for human patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1196-1205, 2018.

Quantification of Wear and Deformation in Different Configurations of Polyethylene Acetabular Cups Using Micro X-ray Computed Tomography

Wear is currently quantified as mass loss of the bearing materials measured using gravimetric methods. However, this method does not provide other information, such as volumetric loss or surface deviation. In this work, we validated a technique to quantify polyethylene wear in three different batches of ultrahigh-molecular-polyethylene acetabular cups used for hip implants using nondestructive microcomputed tomography. Three different configurations of polyethylene acetabular cups, previously tested under the ISO 14242 parameters, were tested on a hip simulator for an additional 2 million cycles using a modified ISO 14242 load waveform. In this context, a new approach was proposed in order to simulate, on a hip joint simulator, high-demand activities. In addition, the effects of these activities were analyzed in terms of wear and deformations of those polyethylenes by means of gravimetric method and micro X-ray computed tomography. In particular, while the gravimetric method was used for weight loss assessment, microcomputed tomography allowed for acquisition of additional quantitative information about the evolution of local wear and deformation through three-dimensional surface deviation maps for the entire cups’ surface. Experimental results showed that the wear and deformation behavior of these materials change according to different mechanical simulations.