Translational Characterization of Macrophage Responses to Stable and Non-Stable CoCrMo Wear and Corrosion Debris Generated In-Situ for Total Hip Replacement.

Metal wear and corrosion debris remain a limiting factor for long-term durability of total hip replacement (THR). Common wear particle production techniques for research differ from the actual tribocorrosion processes at the implant site, potentially causing loss of valuable information. The aim of this study was to investigate reactions to freshly generated and time-stabilized particles and ions released from CoCrMo-alloy using a bio-tribometer, which mimics conditions of the periprosthetic environment. THP-1 macrophages were challenged with freshly produced or time-stabilized wear debris. Wear generation took place in a custom-built bio-tribometer inside a CO2 incubator operating with a reciprocating rotation of an Al2O3 ball against a CoCrMo disc. Two different electrochemical conditions with increasingly forced corrosion rates were tested: +0.45 V (passive domain) and +0.67 V (transition to transpassive domain). Cell viability, proinflammatory cytokines, electrochemical measurements and ICP-MS metal ion content analyses were performed. Cobalt/ chromium concentrations were 6.6/ 1.6 ppm in the passive domain and almost doubled to 11.4/ 3.0 ppm in the passive-transpassive domain. Under those electrochemical conditions, freshly produced and time-stabilized CoCrMo wear decreased cell viability to the same extent. Secretion of proinflammatory cytokines were not significantly different for freshly produced and time-stabilized debris. This study suggests that freshly generated and time-stabilized metal particles/ions cause similar toxicity and inflammatory reactions in macrophages, indicating that standard practices for generating wear debris are valid methods to evaluate wear particle disease. Other cell types, materials, and corrosion potentials need to be studied in the future to solidify the conclusion.

Local Biological Reactions and Pseudotumor-Like Tissue Formation in relation to Metal Wear in a Murine In Vivo Model.

Metal wear debris and released ions (CoCrMo), which are widely generated in metal-on-metal bearings of hip implants, are also found in patients with metal-on-polyethylene bearings due to the mechanically assisted crevice corrosion of modular taper junctions, including head-neck and neck-stem taper interfaces. The resulting adverse reactions to metal debris and metal ions frequently lead to early arthroplasty revision surgery. National guidelines have since been published where the blood metal ion concentration of patients must consistently be monitored after joint replacement to prevent serious complications from developing after surgery. However, to date, the effect of metal particles and metal ions on local biological reactions is complex and still not understood in detail; the present study sought to elucidate the complex mechanism of metal wear-associated inflammation reactions. The knee joints in 4 groups each consisting of 10 female BALB/c mice received injections with cobalt chrome ions, cobalt chrome particles, and ultra-high-molecular-weight polyethylene (UHMWPE) particles or PBS (control). Seven days after injection, the synovial microcirculation and knee joint diameter were assessed via intravital fluorescence microscopy followed by histological evaluation of the synovial layer. Enlarged knee diameter, enhanced leukocyte to endothelial cell interactions, and an increase in functional capillary density within cobalt chrome particle-treated animals were significantly greater than those in the other treatment groups. Subsequently, pseudotumor-like tissue formations were observed only in the synovial tissue layer of the cobalt chrome particle-treated animals. Therefore, these findings strongly suggest that the cobalt chrome particles and not metal ions are the cause for in vivo postsurgery implantation inflammation.