Metallosis Corrosion

Metallosis corrosion-related conditions are mainly focused on the hip joint and related to cobalt ions. At present, cobalt has been studied most, while other metal ions such as titanium and aluminum have not been extensively researched due to their benign reactions to humans. Cobalt–chromium–molybdenum prosthesis is a widely used metal material in orthopedics due to its excellent mechanical properties. These prostheses include the femoral head, cementing the femoral stem and knee components. The cobalt–chromium–molybdenum alloy can form a surface layer of oxide after being exposed to air, which reduces exposure and release of the metal. Nevertheless, after implantation, the ions will be released through physical and chemical reactions, resulting in increased serum cobalt concentration. The metal release of hip prosthesis comes not only from the head–socket interface (like in metal-on-metal (MoM) prosthesis) but also from other metal components. These include the femoral head–stem junction as a fretting interface of the metal parts of modular prosthesis, the collision of metal prosthesis and other parts, the motion of prosthesis inside the cement sleeve or bone when loosening, and the direct reaction of the metal prosthesis in body fluids. Cobalt mainly presents as ions in the human body and is excreted through the kidney. The normal concentration of cobalt ions in the human population is 0.19 μg/L, and the upper limit of 95% confidence interval is 0.42 μg/L. A peripheral blood concentration of 1 μg/L is the limit for industrial overexposure, and a concentration over 5 μg/L is considered harmful. The significant adverse reaction of cobalt in the human body has drawn attention to the extensive implantation of metal-on-metal prosthesis. Our institution conducted relevant studies from January 2016 to December 2018 among revision total hip arthroplasty (THA) patients. Preoperative serum cobalt ion concentration was tested for revision patients with cobalt–chromium–molybdenum prosthesis, among which 27.7% of patients revealed over 0.9 μg/L (38/137). Although higher cobalt concentration alone cannot be considered as an indication of revision THA, understanding the sources of metal ion release and the incidence of abnormal ion concentration is of great significance for the comprehension of THA failure patterns, grasp of surgical indications, surgical decision-making, and the selection of prosthesis for surgeons. Bradberry et al. summarized 18 cases of systemic toxicity related to elevated cobalt ion concentration, which mainly involved heart, thyroid, nervous, and visual systems. There were two main categories: one group used the MoM prosthesis of eight patients with initial THA, of which the ASR prosthesis of Johnson & Johnson was the majority. The cobalt ion concentration of patients was 34.5 (ref range: 13.6–6521) μg/L. For patients with metal-on-metal prosthesis using cobalt–chromium–molybdenum material for the friction interface, the change in serum cobalt concentration is associated with various factors, including prosthesis design, femoral head diameter, and the placement of the prosthesis during operation. DeHaan et al. reported that the serum cobalt ion concentration of patients with well-functioning MoM prosthesis was 2.4 μg/L, while that of patients with prosthesis malposition was 9.8 μg/L. Due to the damage to the bone matrix and soft tissue, revision THA related to adverse reactions to metal has a higher chance of developing complications, associated with a higher rate of infection, prosthesis instability, and loosening. Crawford et al. conducted a follow-up examination of 203 MoM hip revision cases, in which the Harris score improved from 53.6 (preoperative) to 73.5 (postoperative). Notably, 14% of the patients (28 cases) required reoperation, and 16 cases required multiple revisions. Patients with pseudotumors had a significantly increased risk of revision. The survivorship at 4.2 years was 90.5%. Therefore, detailed communication with patients before the operation is necessary. They must be informed of perioperative risks and long-term effects. Fortunately, the revision of adverse reactions to metal related to metal-on-metal friction interface has been undergoing renovation for more than a decade. With the withdrawal of many MoM prostheses and the declined application, serious adverse reactions related to metal ions will not be reported in large amounts. Lainiala et al. reported that of 730 metal-on-metal revision cases in the JOA journal in 2019, the largest number of revision cases appeared between 2011 and 2013, and then the number decreased each year. There are corresponding guidelines on the use of MoM prosthesis and follow-up examinations in countries such as the UK and the US. Due to the late introduction to the domestic market, patient numbers with MoM prosthesis are relatively few. Although there have been no published guidelines for a follow-up examination, it is necessary to conduct a corresponding follow-up examination referring to the experience and data from other countries in order to avoid serious complications. The second category was revision of ceramic component fracture with metal head, ten cases in total. The serum cobalt ion concentration was 506 (353–6521) μg/L. There was an abnormal increase in serum cobalt concentration caused by direct contact between the femoral head and the cup due to PE wearing through, which suggested that follow-up examination should be intensified, especially for patients who underwent an operation before 10 years or more. PE liner wearing through, fracture, and dislocation should be early detected at follow-up.