What is metallosis?
Metallosis is a complication of metal-on-metal implants used predominantly for THAs. It occurs in 1% of patients by 5 years. The metal implants contain chromium and cobalt which can be released as wear particles during use. The metal debris (particularly cobalt) is highly reactive and attracts lymphocytes more than macrophages. This can cause a cytotoxic local tissue effect and/or a hypersensitivity reaction. This can lead to necrosis/fibrosis of periprosthetic tissue leading to muscle necrosis, osteolysis with loosening, effusions, solid soft tissue masses, and aseptic cysts. Metal ion blood levels (>7 ppb), skin patch testing, and lymphocyte transformation tests are used for diagnosis but give inconsistent results so infection should always be ruled out first.
In addition, metal ions can gain entry to the blood stream and cause heavy metal poisoning characterized by skin rashes, cardiomyopathy, hearing and vision problems, depression, cognitive difficulties, renal impairment, and thyroid dysfunction. These patients typically have high metal ion blood levels (>17–20 ppb) with this complication. Treatment of metallosis requires revision arthroplasty with removal of the metal on metal implant.