Systemic allergic dermatitis caused by cobalt and cobalt toxicity from a metal on a metal hip replacement

An 84-year-old woman with a complex orthopaedic history was referred for patch testing with a severe, generalized pruritic eczematous rash. She had undergone a metal-on-metal (MoM) right total hip replacement (Smith and Nephew R3 acetabular system, R3 acetabular liner Co–Cr, femoral head Co/Cr, and standard stem with titanium) for a fractured femur neck in May 2009. The components of her prosthetic hip included a cobalt–chromium metal head articulating against a cobalt–chromium acetabular insert. Prosthesis misalignment was diagnosed on the basis of poor hip abductor strength, a large prosthetic head (40 mm), and a cup inclination angle of 64◦ (ideally 40–50◦ to optimize wear rates). She subsequently underwent further surgery involving a right abductor muscle repair, which was