METAL (HARDWARE) IMPLANT "ALLERGY"

An essential attribute of all implanted surgical material must be an inherent inertness. Whereas "allergic" reactions to surgical implants are at times suspected, definitive association of a reaction caused by implant material is only rarely documented. Because there is no single source describing the incidence, clinical manifestations, pathogenesis, diagnosis, and management of such reactions, this article reviews the literature and attempts to interpret such "reactions" in light of the present knowledge of allergic and irritant contact metal reactions of the skin and bone. Although the true incidence of contact allergy from orthopedic implants may be rare, contact allergy to metals is one of the most common causes of allergic contact dermatitis (ACD), as reported by both the North American Contact Dermatitis Group (NACDG) and the International Contact Dermatitis Research Group (ICDRG). 45 Nickel, cobalt, and chromium are the most constant offenders of all the allergenic metals. Nickel is the most frequent of all reported metal allergies 10 ; 10% of females are reported to be allergic to nickel. Dotterud and Falk 10 noted an increasing prevalence of nickel sensitivity in 201 school girls, which they ascribed to the higher incidence of ear piercing. They found the prevalence of nickel allergy in girls with pierced ears to be twice as high as in girls without pierced ears (30.8% versus 16.3%, respectively). Nickel sensitivity in 223 boys was much lower, with but a few boys having pierced ears (11/223, or 5%). Nickel allergy has also been reported to be one of the most frequent causes of occupational dermatoses. Of 853 hard-metal workers (485 males and 368 females), approximately 5% (2 males and 38 females) were positive to nickel on patch testing. Eighty-eight percent of the positives reported a history of "costume jewelry allergy" prior to their employment in the hard-metal industry. Forty percent of those allergic to nickel developed a recalcitrant hand eczema during the first year of employment, and 36 of 38 nickel-sensitive women had pierced ears. 43 Not only does nickel produce an eczematous (delayed-type hypersensitivity) reaction, but it has also been reported to cause immediate-type (IgE/mast-cell-induced) allergic reactions. The divalent nickel ion can be antigenic via contact, by ingestion, or by inhalation. The latter antigenic presentations may also cause clinical reactions, such as urticaria, with or without wheezing. Cobalt compounds can produce a wide range of immunologic reactions, plus pose an "irritant-type" problem of skin toxicity, especially in the workplace. Cobalt allergy has been noted to occur concomitantly with nickel allergy. Rystedt and Fisher 43 report an incidence of 25% of nickel-sensitive individuals were also allergic to cobalt. Chromium is one of the less toxic heavy metals, but its salts can induce an irritant contact dermatitis (ICD). Trivalent chromium is the least reactive because of its relative inability to penetrate the skin. Hexavalent chromium, however, is the compound mostly associated with ICD. Many hexavalent chromium compounds are corrosive irritants, sensitizers, and respiratory carcinogens. 19 Sensitization to chromium enhances cobalt sensitization, which frequently occurs in nickel-sensitive individuals. These are not considered to be cross-reactions, but more likely distinctive, unique sensitizations to each individual metal. 24 The prevalence of these metals in the environment is high.