Chromium

Chromium in metal implants and prostheses

Complications from the use of metal implants and prostheses can arise because of biochemical and histological reactions to some of the materials used [ ]. These include titanium, stainless steel (10–14% nickel, 17–20% chromium), and cobalt chrome alloys (27–30% chromium, 57–68% cobalt, and up to 2.5% nickel). All of these metals can produce sensitization or elicit toxic reactions when they are solubilized and come into contact with tissues; it can be difficult or even impossible to differentiate between hypersensitivity and toxic reactions.

Metals from prostheses can continue to be released into the system for many years. The development of hypersensitivity takes time, and allergic reactions are usually delayed for weeks, months, or 1–2 years. The symptoms can assume a variety of forms. Local reactions can cause loosening of the device or local pain. Dermatological reactions include eczema, bullous pemphigoid, urticaria, and “muscle tumors”.

Attempts continue to predict metal sensitivity in the individual patient so that the choice of material can be made accordingly. In vitro tests for metal allergies have been developed on the basis of lymphokine (MIF) release from sensitized T lymphocytes exposed to metal-protein complexes [ ]. About 6% of patients without a previous metal implant had positive reactions to nickel, chromium, or cobalt. However, it is still not clear whether such a positive reaction is a reliable predictor of clinical problems. In practice few patients have either local or systemic reactions; when symptoms occur and other causes are ruled out, the implant should be removed. Some workers recommend removal of an implant whenever there is both a positive MIF test and a positive skin test, even in the current absence of a serious reaction. Allergic dermatitis will clear up as soon as the metal has begun to be cleared from the tissue. The type of metal and the amount released into the tissue will affect the time taken for the disappearance of toxic dermatological phenomena.

Observational studies

The potential human health effects of occupational exposure to cobalt and chromium contaminants with exposure from surgical devices such as orthopedic joint replacements have been reviewed [ ]. Both industrial and surgical exposure cause inflammatory and other immune reactions in the directly exposed tissues. There is a well-established risk of lung cancer after long-term exposures to hexavalent chromium; however, sarcoma in the connective tissues adjacent to implants in response to metal particles is rare. Both types of exposure are associated with changes in the peripheral blood, including evidence of oxidative stress and altered numbers of circulating immune cells. There is dissemination of cobalt and chromium to sites distant to the orthopedic implant, but less is known about systemic dissemination of these metals away from the lung.

There is increasing concern about the health effects (hypersensitivity, osteolysis, carcinogenicity) of metal-to-metal surgical implants. Long-term wear and dissolution of the material can lead to internal exposure. The blood concentrations of chromium and cobalt were followed at 3, 6, 12, and 24 months after a metal-on-metal surface replacement hip arthroplasty using a high carbon content chromium–cobalt alloy implant in 64 patients [ ]. The blood concentrations of chromium and cobalt were significantly increased 3 months postoperatively but gradually fell. At 1 year, mean whole blood ion concentrations were 1.61 μg/l (0.4–5.5) for chromium and 0.67 μg/l (0.23–2.09) for cobalt, both of which are above the reference ranges. The preoperative ion concentrations, component size, female sex, and the inclination of the acetabular component were inversely proportional to the chromium and/or cobalt ion concentrations at 1 year postoperatively. Other factors, such as age and activity, did not correlate with the metal ion concentrations. The authors concluded that these concentrations may be specific to the hip resurfacing implant and have diagnostic value.