According to the FDA, metal-on-metal hip implants have unique risks beyond those of all artificial hip implants. In a metal-on-metal hip implant, the metal ball and the metal cup of the device slide against each other during everyday motions such as walking or running. This friction may cause tiny metal particles to wear off. Corrosion at the connection between the metal ball and taper of the stem may also occur, causing metal ions (e.g. cobalt and chromium) to enter the bloodstream and build up in the soft tissue surrounding the device, causing metal toxicity. This type of metal poisoning is often called metallosis.
While patients may react to metal poisoning differently, over time, the metal particles often cause a reaction around the joint that results in tissue damage. Adverse events such as hip/groin pain, swelling, numbness, difficulty walking, skin rash and auditory or visual impairments may occur. These side-effects can lead to bone loss, implant loosening, early device failure, and even revision (replacement) surgery to prevent further injury.
Implant recipients experiencing symptoms should make an appointment to see their orthopedist, the FDA advises. To evaluate patient symptoms, orthopedic surgeons may order blood tests (including checking levels of metal ions in the blood), perform soft tissue imaging, or extract fluid from around the joint. The FDA also recommends that even asymptomatic patients with metal-on-metal hip implants should follow-up with their orthopedic surgeon every 1 to 2 years to monitor potential damage.