Biological effects of metal degradation in hip arthroplasties.

Metals and metal alloys are the most used materials in orthopedic implants. The focus is on total hip arthroplasty (THA) that, though well tolerated, may be associated with local and remote adverse effects in the medium-long term. This review aims to summarize data on the biological consequences of the metal implant degradation that have been attributed predominantly to metal-on-metal (MoM) THA. Local responses to metals consist of a broad clinical spectrum ranging from small asymptomatic tissue lesions to severe destruction of bone and soft tissues, which are designated as metallosis, adverse reactions to metal debris (ARMD), aseptic lymphocytic vasculitis associated lesion (ALVAL), and pseudotumors. In addition, the dissemination of metal particles and ions throughout the body has been associated with systemic adverse effects, including organ toxicity, cancerogenesis, teratogenicity, and immunotoxicity. As proved by the multitude of studies in this field, metal degradation may increase safety issues associated with THA, especially with MoM hip systems. Data collection regarding local, systemic and long-term effects plays an essential role to better define any safety risks and to generate scientifically based recommendations.

Serum levels of osteoprotegerin and receptor activator of nuclear factor-kappaB ligand as markers of periprosthetic osteolysis.

BACKGROUND: Previous studies have suggested that the balance between receptor activator of nuclear factor-kappaB ligand (RANKL) and its decoy-receptor osteoprotegerin (OPG) in local tissue seems to play a crucial role in the loosening of the total hip replacement. The aim of this study was to evaluate whether the circulating levels of OPG and RANKL, as well as their ratio, could be different in patients with aseptic loosening compared with patients with stable implants. METHODS: One hundred and twenty-eight subjects were recruited. They included thirty-nine patients with osteoarthritis who had not yet undergone total hip arthroplasty, thirty-three patients who had undergone total hip arthroplasty and had clinically and radiographically stable implants, thirty-six patients with aseptic loosening of total hip arthroplasty components, and twenty healthy volunteers. Serum levels of OPG and RANKL were measured with use of an immunoenzymatic method, and in each individual the OPG-to-RANKL ratio was calculated. RESULTS: In every group, a significant correlation was detected between OPG concentration and age (r = 0.58, p < 0.0001), especially in individuals older than fifty years, while gender and underlying disease were not found to influence serum levels of the tested parameters. In comparison with the levels in healthy donors and patients with a stable total hip replacement, the serum levels of OPG were increased in the patients who had not yet had an arthroplasty, those with aseptic loosening of a total hip replacement, and those with a cemented total hip replacement. Moreover, the OPG serum level provided good diagnostic accuracy in detecting the implant failure. A correlation was found between the sum of the osteolytic areas seen radiographically around the femoral stem and the RANKL level (r = 0.38, p = 0.02) and the OPG-to-RANKL ratio (r = -0.29, p = 0.04). CONCLUSIONS: An increase in OPG levels may reflect a protective mechanism of the skeleton to compensate for the osteolytic activity that occurs in severe osteoarthritis and in aseptic loosening. Prospective studies are needed to determine whether serum OPG levels could be used as markers for monitoring the stability of the implant, as well as for predicting aseptic loosening. LEVEL OF EVIDENCE: Diagnostic study, Level III. See Instructions to Authors for a complete description of levels of evidence.