Orthopaedic metallic implants in extremity fractures and contact allergy

Indications for and Risks Associated With Implant Removal After Pediatric Trauma

A wide range of implants are used in the treatment of pediatric fractures, including wires, plates, screws, flexible rods, rigid rods, and external fixation devices. Pediatric bones differ from adult bones both mechanically and biologically, including the potential for remodeling. Implants used in pediatric trauma patients present a unique set of circumstances regarding indications, risks, timing of implant removal, weight-bearing restrictions, and long-term sequelae. Indications for implant removal include wire/pin fixation, when substantial growth remains, and infection. When considering implant removal, the risks and benefits must be assessed. The primary risk of implant removal is refracture. The timing of implant removal varies widely from several weeks to a year or more with the option of retention depending on the fracture, type of implant, and skeletal maturity of the patient.

Allergic or Hypersensitivity Reactions to Orthopaedic Implants

Allergic or hypersensitivity reactions to orthopaedic implants can pose diagnostic and therapeutic challenges. Although 10% to 15% of the population exhibits cutaneous sensitivity to metals, deep-tissue reactions to metal implants are comparatively rare. Nevertheless, the link between cutaneous sensitivity and clinically relevant deep-tissue reactions is unclear. Most reactions to orthopaedic devices are type IV, or delayed-type hypersensitivity reactions. The most commonly implicated allergens are nickel, cobalt, and chromium; however, reactions to nonmetal compounds, such as polymethyl methacrylate, antibiotic spacers, and suture materials, have also been reported. Symptoms of hypersensitivity to implants are nonspecific and include pain, swelling, stiffness, and localized skin reactions. Following arthroplasty, internal fixation, or implantation of similarly allergenic devices, the persistence or early reappearance of inflammatory symptoms should raise suspicions for hypersensitivity. However, hypersensitivity is a diagnosis of exclusion. Infection, as well as aseptic loosening, particulate synovitis, instability, and other causes of failure must first be eliminated.

Inhalation toxicity of 316L stainless steel powder in relation to bioaccessibility

The Globally Harmonized System for Classification and Labelling of Chemicals (GHS) considers metallic alloys, such as nickel (Ni)-containing stainless steel (SS), as mixtures of substances, without considering that alloys behave differently compared to their constituent metals. This study presents an approach using metal release, explained by surface compositional data, for the prediction of inhalation toxicity of SS AISI 316L. The release of Ni into synthetic biological fluids is >1000-fold lower from the SS powder than from Ni metal, due to the chromium(III)-rich surface oxide of SS. Thus, it was hypothesized that the inhalation toxicity of SS is significantly lower than what could be predicted based on Ni metal content. A 28-day inhalation study with rats exposed to SS 316L powder (<4 µm, mass median aerodynamic diameter 2.5–3.0 µm) at concentrations up to 1.0 mg/L showed accumulation of metal particles in the lung lobes, but no signs of inflammation, although Ni metal caused lung toxicity in a similar published study at significantly lower concentrations. It was concluded that the bioaccessible (released) fraction, rather than the elemental nominal composition, predicts the toxicity of SS powder. The study provides a basis for an approach for future validation, standardization and risk assessment of metal alloys.

Correlation between metal allergy and treatment outcomes after ankle fracture fixation

PURPOSE

To determine correlation between metal hypersensitivity and long-term foot and ankle function and pain after internal fixation using stainless steel implants.

METHODS

60 men and 46 women (mean age, 47 years) who underwent internal fixation for ankle fractures completed a questionnaire 13 to 38 (mean, 26) months after surgery to assess their existing medical condition, history of metal hypersensitivity, problems and outcome of the implant (revision or removal), and the American Academy of Orthopaedic Surgeons (AAOS) foot and ankle score. A subset of 12 men and 15 women then underwent patch testing for metal hypersensitivity to molybdenum, chromium, iron, manganese, and nickel. Patients with positive and negative reactions were compared.

RESULTS

21 of the 106 patients underwent removal of the metal implants. The AAOS score was not associated with any of the variables, except for a history of metal hypersensitivity from dental implants and irritation around the surgical scar. Multiple linear regression analysis showed that only irritation around the surgical scar remained associated with poorer AAOS scores. Five of the 27 tested patients had a positive reaction. The mean AAOS scores did not differ significantly between patients with positive and negative reactions (34 vs. 31, p=0.73). Gender was not associated with the test results (p=0.63). None of the 5 patients with a positive reaction underwent revision surgery or reported any history of asthma or metal hypersensitivity. Of the 27 patients, one of the 8 who reported itching, irritation, redness or rash around the surgical scar had a positive reaction, compared to 4 of 19 patients who reported no such symptoms (p=1). Two of the 27 patients reported development of eczema after fixation, one of whom had a positive reaction. Only one of the 27 patients reported a history of metal hypersensitivity to jewellery, but had a negative reaction..

CONCLUSION

Neither a history of metal hypersensitivity nor positive patch testing correlated with poor outcomes after internal fixation for ankle fractures using stainless steel implants.

Metal sensitivities and orthopaedic implants revisited: the potential for metal allergy with the new metal-on-metal joint prostheses

The potential of metal-containing orthopaedic prostheses to induce problems through metal allergy taxes dermatologists and orthopaedic surgeons alike. Metal-on-plastic joint replacements are not thought to induce metal allergy but wear products, principally polypropylene particles, produce a foreign body reaction in bone and may lead to aseptic loosening of the joint. Orthopaedic surgeons are increasingly using metal-on-metal joint replacements, particularly for younger patients, as some evidence suggests that there is less wear debris and hence less aseptic loosening. The original metal-on-metal hip joints of the 1960s were associated with sensitivities to cobalt, nickel and chromate when loosening occurred. The potential for modern metal-on-metal joint prostheses, with their lower production of wear debris, to sensitize the recipient to metals or to induce a problem in subjects already allergic to metals, is unclear. One uncontrolled series suggested an association between nickel allergy and prosthesis loosening in some subjects, but the question has yet to be addressed in a prospective study and to date there is no other observation in the orthopaedic literature to suggest a problem.