The Significance of Nonlinear Motion in the Wear Screening of Orthopaedic Implant Materials

Abstract

Linear reciprocating pin-on-plate-type wear testing has been a standard technique for the screening of orthopaedic implant materials since the early 1980s. This investigation compares a wear screening technique based on linear motion with a modern hip joint simulator based on multi-axial motion. Two groups of differently sterilized UHMWPE samples were tested. The first group of samples was sterilized by ethylene oxide (EtO) gas that caused no structural changes in the UHMWPE. The second group of samples was sterilized in nitrogen by gamma-irradiation and then subjected to a stabilization treatment that resulted in a significant level of crosslinking in the UHMWPE. When tested on the linear reciprocating wear machine, the EtO sterilized specimens (non-crosslinked linear polyethylene) showed an approximately 30% lower wear rate than the gamma-irradiated and stabilized specimens (crosslinked polyethylene). When tested on the hip simulator, the EtO sterilized specimens exhibited two to three times higher wear rates than the gamma irradiated and stabilized specimens. The ranking of wear resistance obtained with the hip simulator was strikingly different than that obtained with the linear reciprocating wear machine. This study indicates that screening wear machines based on linear motion do not correlate with multi-axial joint simulators and may produce misleading results in the prediction of clinical wear performance of UHMWPE bearing materials.

Finite Element Simulations of Hard-On-Soft Hip Joint Prosthesis Accounting for Dynamic Loads Calculated from a Musculoskeletal Model during Walking

“…It is well known that wear tests that are close to the in vivo conditions have a long duration and elevate costs [ 1 , 10 , 11 ]. The wear simulation is run for several million cycles, considering that one million cycles corresponds to one year in vivo [ 12 , 13 , 14 ]. The running-in period encompasses approximately the first half a million cycles; the steady-state wear is assessed by measuring the wear after the running-in period [ 15 ].…”

Microtextured CoCrMo alloy for use in metal-on-polyethylene prosthetic joint bearings: Multi-directional wear and corrosion measurements

“…Borjali et al [26] recently demonstrated significantly reduced wear of UHMWPE, highly-crosslinked polyethylene (HXPE), and vitamin E-infused highly-crosslinked polyethylene (VEXPE) pins articulating with a microtextured CoCrMo surface specifically designed to create microhydrodynamic bearings. However, only uni-directional shear between the polyethylene pins and the CoCrMo surface was evaluated, whereas multidirectional shear is well-known to increase polyethylene wear [27]. In addition, none of the works documented in the literature have evaluated the effect of laser surface texturing on corrosion resistance of the CoCrMo alloy.…”

Multidirectional Pin-on-Disk Testing Device to Evaluate the Cross-shear Effect on the Wear of Biocompatible Materials

“…The first wear testers relied on Archard's law, where the wear rate only depends on load and sliding distance [16]. From different studies [17,18], wear rates obtained from reciprocating and unidirectional motion were lower, by two to three orders of magnitude compared to in vivo wear rates of UHMWPE. Since very early, it was stated that multidirectional motion was a large accelerator of UHMWPE wear, and there was a necessity for multidirectional pin-on-disk testing to obtain physiologically realistic levels of wear in artificial joints with UHMWPE bearings [15,19,20].…”