Comparison of in vitro with in vivo characteristics of wear particles from metal–metal hip implants

Abstract

The purpose of the present study was to compare wear particles isolated from metal-metal (MM) hip implants worn in an orbital bearing simulator with particles from similar MM total hip replacement (THR) implants worn in vivo. Comparison of these particles is important because it will help to assess the overall suitability of this type of hip simulator for reproducing in vivo wear and for producing physiological wear particles suitable for biological studies of in vitro cellular response. Commercial grade components made of ASTM F75 (cast) alloy were evaluated. Simulator tests were performed in 95% bovine calf serum with a 28-mm-diameter implant. Wear particles were collected from 0 to 0.25 million cycles (run-in wear period) and 1.75 to 2 million cycles (steady-state wear period). Tissues from seven patients with MM implants (surface replacement or stem type) were harvested at revision surgeries (after 1-43 months). Metal wear particles were isolated from serum lubricant or tissues using an enzymatic protocol that was previously optimized to minimize particle changes due to reagents. After isolation, particles were centrifuged, embedded in epoxy resin, and characterized by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDXA). Results of EDXA on particles from the hip simulator primarily indicated a predominance of particles containing Cr and O but no Co (most likely chromium oxide particles), and fewer CoCrMo particles presenting varying ratios of Co and Cr. Image analysis of TEM micrographs demonstrated that the majority of the particles from the simulator were round to oval, but a substantial number of needle-shaped particles were also found, especially from 0 to 0.25 Mc. The particles generated from 0 to 0.25 Mc had an average length of 53 nm, whereas those generated from 1.75 to 2 Mc had an average length of 43 nm. In vivo, EDXA and TEM analysis of particles that were retrieved from two patients at 23 and 43 months respectively, revealed that they were the most comparable in composition, average length (57 nm), and shape to particles generated in the hip simulator during the run-in wear period. Because a large clinical retrieval study in the literature suggested that a run-in wear regime might occur in vivo for some 6-36 months, the fidelity of the simulator of the present study was strongly supported. However, some uncertainties existed, including the finding that the particles isolated from the other five patients generated from 1 month up to 15 months (shorter implantation times than the other two patients) were smaller and mostly contained only Cr and O (no Co). In the opinion of the authors, this particular very short term patient group was somewhat atypical. Therefore, despite these uncertainties, the present study was deemed to support the ability of the orbital bearing hip simulator to produce physiological wear particles.

Trivalent and Hexavalent Chromium Issues in Medical Implants

“…These corrosion products could then change the macrophage cell behavior [13,14,20]. Their data support the hypothesis that macrophage cells and their RCS affect alloy corrosion and that changes in alloy corrosion by cells may be important in the development of host responses to the alloy and its corrosion products.…”

Wear of CoCrMo alloys used in metal-on-metal hip joints: A tribocorrosion appraisal

“…The number of loading cycles varies typically from 3 up to 10 Mcycles at frequencies of 1 or 1.13 Hz. Table 2 summarizes the key features of published papers on the characterisation of metal on metal CoCrMo artificial hip joints using simulators [12,[46][47][48][49][50][51][52][53][54][55][56][57][58]. Among the authors, only Yan [49] measured the evolution of open circuit potential during a simulator test.…”

Wear debris from hip prostheses characterized by electron imaging

“…For the former, wear debris has been isolated from periprosthetic tissue. To digest the tissue, alkaline, acid [18,19] and enzyme digestion techniques have been used [20][21][22]. When using acid or alkaline chemical reagents, however, metal particle size and shape may change [18].…”