Biological effects of clinically relevant wear particles from metal-on-metal hip prostheses

Abstract

The problems of osteolysis and late aseptic loosening associated with ultra-high molecular weight polyethylene (UHMWPE) particles has lead to a renewed interest in metal-on-metal prostheses. Wear particles generated by modern Co-Cr-on-Co-Cr prostheses are nanometre in size (range: 10-120 nm; mean: about 40 nm), an order of magnitude smaller than the size of UHMWPE known to be critical for activation of osteolytic cytokines by macrophages. Co-Cr wear particles will induce osteolytic cytokine production by human macrophages, but only at high volumetric concentrations. Unlike UHMWPE, Co-Cr particles are not inert. Co-Cr particles have the potential to release metal ions; they may be toxic to cells, induce deoxyribonucleic acid damage or cause host hypersensitivity. The nanometre size range of Co-Cr wear particles means that they may be disseminated widely in the body. The potential for metal-on-metal bearings to induce adverse effects clinically will be dependent upon the rate of wear. What constitutes a safe wear rate for modern metal-on-metal bearings is unknown. However, the wear of metal-on-metal prostheses is critically dependent upon the design and, in particular, the carbon content of the alloy, the radial clearance, and the head diameter. Thus, the potential for adverse biological reactions associated with metal-on-metal bearings can be reduced by selection of appropriately designed implants.

Reduced Articular Surface of One-piece Cups: A Cause of Runaway Wear and Early Failure

“…Elevated chromium and cobalt levels have been found in both the serum and remote organs of patients with metal-on-metal bearings [1,2,10]. Studies have also demonstrated excessive wear with onepiece metal shells in women with smaller diameter components as well as in hips in which the shell is oriented more vertically in the pelvis (a higher abduction angle) [5,11,13,16,19].…”

Perivascular Lymphocytic Infiltration Is Not Limited to Metal-on-Metal Bearings

“…Ions can be generated from not only corrosion but also repassivation, modular components, delaminated metal coatings, impingement, and fixation screws [24,30]. Although metal ions disseminate throughout the reticuloendothelial system at less than toxic levels [1,8], metal particles can concentrate locally in the periprosthetic soft tissue [16] causing metallosis [9] and frank tissue necrosis [3]. Histologic studies of MoM periprosthetic tissue have identified a characteristic pattern of DLI in the inner neocapsular layer and PVLI in the intermediate vascular layer [39,40] suggestive of a DTH reaction.…”

Hypersensitivity Reactions to Implanted Metal Devices: Facts and Fictions

“…MoP implants generally produce a higher volume of wear particles than MoM implants, but the latter generate a larger number of particles, as metal particles are an order of magnitude smaller [55][56][57][58][59]. The adaptive immune system reacts differently to MoM and MoP implants: unlike MoM implants, a specific cell-mediated response to ultrahigh molecular weight polyethylene (UHMWP) does not appear to play a major role in MoP implant loosening.…”