Abstract

Objective/Aim/Hypothesis: Aseptic prosthetic loosening is a major problem of total hip arthroplasty (THA). In addition to the considerable suffering of the affected patient, it usually leads to a complex prosthetic replacement requiring long-term rehabilitation with considerable costs involved. An inflammatory reaction within the periprosthetic tissue due to wear particles is considered a main contributing factor of aseptic loosening of the prosthesis. While the mechanisms are understood incompletely, it is known that wear particles of different materials are able to trigger different inflammatory reactions. Particularly, wear debris of metal-on-metal bearings have caused heavy tissue reactions and periprosthetic pseudotumorous. The aim of the present study was the in vivo investigation of the inflammatory activity of metallic degradation products. The focus was to elucidate the reaction of cobalt and chromium ions, as well as of CoCr29Mo6 metal wear particles and of ultra-high-molecular-weight polyethylene (UHMWPE) compared to the reaction to a control group (PBS). Design/Approach/Methods: Data from the present study were collected using an established murine in vivo inflammatory. The Balb/c mice were randomized in four treatment groups of 10 animals each. 50µl of CoCr29Mo6 metal particles [0,1 Vol.-% - 8,3 mg/ml], metal ions [200 µg / l], UHMWPE particles [0,1 Vol.-%] suspension or physiological PBS solution [0,1 Vol.-%] for the control group were injected into the knee joints of the animals on day 1. After one week of incubation, the patellar tendon was partially resected to visualize the synovial tissue. To assess the synovial microcirculation, the fluorescent markers FITC-dextran and rhodamine 6G were injected intravenously and the in vivo imaging via fluorescence microscopy was performed. A histological examination after hematoxylin-eosin using an established inflammatory score and measuring the thickness of the synovial membrane followed this procedure. Results: There was a significant enhanced leukocyte-endothelial cell interaction as reaction to metal (p<0.001) and polyethylene particles (p<0.001) in comparison to the control group, but no significant difference between PBS and the metal ion group (p=0.190). The functional capillary density was significantly increased after exposure to polyethylene particles (p=0.003) and tendentially increased after the incubation with metal particles (p=0.023) compared to the control group. There was no difference detectable between the control and the metal ion group (p=0.247). After the exposition to metal ions (p<0.001), and polyethylene particles (p<0.001), a significant, but moderately thickening of the synovial membrane occurred. Within the metal particle group, a massive proliferated synovial membrane was found (p<0.001). The inflammatory score increased over all groups in comparison to PBS. For the metal ion (p=0.003) and polyethylene groups (p=0.002) to the same extent, but to a much higher extent for the metal particle group (p<0.001). Conclusions: The results of this experimental study suggest, that metal particles are strong inducers of an inflammatory reaction and able to cause pseudotumor-like tissue formations. It can be also concluded, that metal ions by themselves are capable to evoke an inflammatory reaction, independent of metal particles. Suggesting that metal ions play an important role in the periprosthetic reaction to metallic wear. (UHMW-) polyethylene particles trigger an inflammatory reaction, too and we could detect histologically osseous changes.