Follow-up of patients who have received a metal-on-metal hip implant should include periodic physical examinations and imaging tests, and in some cases, measurements of metal ion levels in the blood, according to the Food and Drug Administration update on the safety these devices.
The update, released in January, states that these devices – made up of a metal ball, stem, and socket – "have unique risks in addition to the general risks of all hip implants," and include soft tissue damage caused by the release of tiny metal particles from the metal surfaces sliding against each other over time. This soft tissue damage can be associated pain, loosening of the implant, and may require revision surgery.
The release of metal ions (which may include cobalt and/or chromium) into the bloodstream may cause a systemic reaction, but at this time, "the FDA does not have enough scientific data to specify the concentration of metal ions in a patient’s body or blood necessary to produce adverse systemic effects," the statement said, adding that this reaction "seems to be specific to individual patients, with different patients having different reactions to the metal wear particles."
The recommendations in the safety update are largely directed at orthopedic surgeons, who are advised to follow-up with patients who are asymptomatic metal-on-metal hip implant recipients with a physical exam and routine x-rays every 1 to 2 years, paying close attention to the signs and symptoms that these implants may cause. Patients who are symptomatic should be followed at least every 6 months.
But since people who have these implants and are experiencing systemic symptoms are more likely to see their primary care physician or rheumatologist, it is "important for all health care providers to be aware of metal ion adverse events that may occur in metal-on-metal hip implant patients," the FDA statement said.
These adverse events, which the statement says are based on case reports, "may include" a general hypersensitivity reaction (skin rash), cardiomyopathy, neurologic changes (including sensory changes such as auditory or visual impairment), renal function impairment, and thyroid dysfunction (including neck discomfort, fatigue, weight gain, or feeling cold).
Other recommendations include consideration of metal ion testing in patients with symptoms or physical signs that the device may not be functioning properly.
The safety update and recommendations are based on the agency’s evaluation of the published literature, and recommendations made at a June 2012 Orthopaedic and Rehabilitation Devices Advisory Panel meeting.
The metal-on-metal hip resurfacing systems became popular in younger active patients who had healthier bone and were thought to last longer, but their use has declined in reaction to increased revision rates and reports of adverse events, and has resulted in FDA recalls of some devices. The orthopedic surgeons on that panel indicated that they rarely or never used these implants anymore.
In December 2012, the American Academy of Orthopaedic Surgeons, the American Association of Hip and Knee Surgeons, and the Hip Society issued a statement on these devices, which said that recent reports from national joint registries have reported that the failure rates of total hip replacement surgery using metal-on-metal implants are two- to threefold higher than "contemporary" total hip replacement surgery using non–metal-on-metal devices. More than 10,000 metal-on-metal implants have been implanted worldwide since 1996, the statement said.
To view the FDA safety statement, click here. Adverse events associated with metal-on-metal hip implants should be reported to the FDA’s MedWatch program online or at 800-332-1088.