• Hip and knee surgery

Abstract Degenerative joint diseases constitute an increasing problem in public health and are among the most prevalent diseases that affect humans. In Denmark approximately 500.000 people live with the disease, and hip osteoarthrosis alone accounts for 8000 primary joint arthroplasties yearly [1,2]. The present treatment of end-stage degenerative joint disorder relies on replacement surgery using joint arthroplasties. While joint replacement provides compelling pain relief and restoration of function, there is great room for improvement. Despite major advances during the last decades serious problems exist concerning long-term durability and rejection of the artificial joint implants. Ten percent of patients undergoing hip joint replacement will develop periprosthetic bone destruction within 10 years of surgery [3,4]. As an answer to these demands very durable bearings are being developed such as metal-onmetal hip replacements made of CoCrMo alloy. But biocompatibility may be compromised because of macrophage interaction with alloy bulk, particulate wear-debris, and metal ions liberated from the alloys. Aim of the experimental studies The aim of the presented experimental studies was to evaluate the biocompatibility of CoCrMo alloy in light of the macrophage mediated (dissolucytosis) metal release [5]. The alloy was studied in three different experimental models. First, an in vivo study investigating the release and spreading of metal ions from implants not subjected to any mechanical wear. Secondly, in vitro studies isolating the impact of the alloy on macrophages, and thirdly, an in vivo study investigating the influence of the alloy on implant osseointegration. Hypotheses We hypothesized that intraperitoneal and intramuscularly implanted CoCrMo wire would release metal ions that would be accumulated in kidney and liver. We further hypothesized that the increased metal ion levels would increase metallothioneine expression in kidney and liver. We hypothesized that CoCrMo alloy would prove less biocompatible and generate a larger macrophage pro-inflammatory response compared to TiAlV alloys. We further hypothesized, that adding hydroxyapatite would increase biocompatibility and decrease macrophage proinflammatory response. We hypothesized that Titanium PoroCoat® would prove a superior overall performance compared to CoCrMo PoroCoat®. Results Animals with intramuscular CoCrMo implants accumulated metal in liver and kidney and metallohionein I/II were elevated in liver tissue. We observed that as-cast high carbon CoCrMo reduced the pro-inflammatory macrophage cytokine response, and that hydroxyapatite coating increased the pro-inflammatory response. Osseointegration was not statistically significant affected by CoCrMo; however, a statistical significant decreased mechanical implant fixation, could be recognized. Conclusion In conclusion, these results substantiate considerations regarding the use of CoCrMo. The short-term biocompatibility was affected by a decreased mechanical implant fixation; however, the osseointegration was not affected. The long-term biocompatibility is still to be revealed. A continuous burden of wear particles and metal ions should be encountered, and theoretically many untoward effects may exist.

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