The FDA issued a proposed order requiring manufacturers of metal-on-metal total hip replacement systems to submit premarket approval (PMA) applications. Metal-on-metal total hip replacement systems were marketed in the U.S. prior to 1976 legislation that gave the agency premarket authority over medical devices. As “preamendment devices,” they were designated as Class III (higher risk) devices but were regulated under the 510(k) premarket notification program.
The FDA is providing updated safety information based on its current assessment of metal-on-metal hip implants, including the benefits and risks, the evaluation of the published literature, and the results of the June 2012 Orthopedic and Rehabilitation Devices Advisory Panel meeting. On May 6, 2011, the FDA instructed manufacturers of metal-on-metal total hip replacement (THR) systems to conduct a postmarket surveillance study of these devices. Five manufacturers currently market metal-on-metal hip implants in the U.S. and all five have approved postmarket surveillance study plans. Data from these studies will provide patients and health care providers with additional information about the safety profiles of the implants, including the effect of metal ion concentrations in the bloodstream. On June 27-28, 2012, the FDA convened the Orthopaedic and Rehabilitation Devices Panel of the Medical Devices Advisory Committee to seek expert scientific and clinical opinion on the benefits and risks of metal-on-metal hip systems. Information from this panel meeting has helped form these recommendations.
Hip joint deterioration can lead to pain, stiffness or difficulty walking. When these symptoms do not respond to conservative treatment, such as physical therapy, patients may be advised to undergo total hip replacement or hip resurfacing. As part of this treatment, they may receive a “metal-on-metal” hip implant in which the “ball and socket” of the device are both made from metal. Metal-on-metal hip implants consist of a ball, stem and shell, all made from cobalt-chromium-molybdenum alloys. There are two types of metal-on-metal hip implants: traditional total hip replacement systems and resurfacing hip systems.
All artificial hip implants carry risks including wear of the component material. Metal-on-metal (MoM) hip implants have unique risks in addition to the general risks of all hip implants.
In MoM hip implants, the metal ball and the metal cup slide against each other during walking or running. Metal can also be released from other parts of the implant where two implant components connect. Metal release will cause some tiny metal particles to wear off of the device into the space around the implant. Wear and corrosion at the connection between the metal ball and taper of the stem may also occur. Some of the metal ions (e.g. cobalt and chromium) from the metal implant or from the metal particles will enter the bloodstream.
Orthopedic surgeons take several precautions before and during hip replacement surgery to try to optimize the way in which the ball and socket rub against each other so that fewer wear particles are produced. However, there is no way to fully avoid the production of some metal particles.
Different people will react to these metal particles in different ways. At this time, it is not possible to predict who will experience a reaction, what type of reaction they might have, when the reaction will occur, or how severe the reaction will be.
Over time, the metal particles around some implants can cause damage to bone and/or tissue surrounding the implant and joint. This is sometimes referred to as an “adverse local tissue reaction (ALTR)” or an “adverse reaction to metal debris (ARMD).” Soft tissue damage may lead to pain, implant loosening, device failure, and the need for revision surgery in which the old device is removed and replaced with another one. Patients with a progressing ALTR may be considered for earlier revision to prevent extensive damage to bone, muscle and nerves.
International regulatory agencies have issued alerts and safety communications related to MoM hip implants. In April 2010, the United Kingdom's Medicines and Healthcare products Regulatory Agency (MHRA) issued a medical device alert that included specific follow-up recommendations for patients with MoM hip replacements. The recommendations included blood tests and imaging for patients with painful MoM hip implants. In February 2012, MHRA published a medical device alert and updated it in June 2012 with advice on the management and monitoring of patients with MoM hip systems. In May 2012 Health Canada issued a public health communication to orthopedic surgeons and patients regarding MoM hip implants. The Therapeutic Goods Administration of Australia published their safety information for healthcare professionals on MoM hips in September 2012.
There are also reports in orthopedic literature, data from international orthopedic implant registries and presentations from professional/scientific meetings that have increasingly noted complications and potential problems of early failure of MoM hip systems, often requiring revision surgery. Much of the available data are from countries outside the U.S., and the data may not be directly applicable to the experience in the U.S. For example, some of the devices available outside of the U.S. are not marketed in the U.S. For this reason, recommendations from international regulatory agencies may not necessarily apply to U.S. patients with MoM hip systems.
If patients with MoM hip implants develop any symptoms that may indicate that their device is not functioning properly, it is very important for them to make an appointment with their orthopedic surgeons promptly for further evaluation. Aside from a physical exam of the hip, the orthopedic surgeon may consider several tests to evaluate these symptoms including using a needle to remove fluid from around the joint, known as joint aspiration; soft tissue imaging; and blood tests, including checking levels of metal ions in the blood.
Patients who receive MoM hip implants should also pay close attention to changes in their general health including new or worsening symptoms outside their hip. If they are referred to a doctor to evaluate new conditions, they should let their physician know they have a MoM hip implant. There have been some case reports and articles in the medical literature that suggest patients with a MoM hip implant may have certain symptoms or illnesses elsewhere in the body. These systemic reactions include:
- General hypersensitivity reaction (skin rash)
- Neurological changes including sensory changes (auditory, or visual impairments)
- Psychological status change (including depression or cognitive impairment)
- Renal function impairment
- Thyroid dysfunction (including neck discomfort, fatigue, weight gain or feeling cold
Metal-on-metal implant patients with systemic symptoms are more likely to visit their primary care practitioner than their orthopedic surgeon, which makes it important for all health care providers to be aware of metal ion adverse events that may occur in metal-on-metal hip implant patients. Patients with systemic findings that are thought to be related to a metal-on-metal hip implant should be advised to follow-up with his or her orthopedic surgeon to determine the appropriate course of action.
Presently, 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. In addition, the reaction seems to be specific to individual patients, with different patients having different reactions to the metal wear particles. At the current time, there is not enough evidence to support the routine need for checking metal ion levels in the blood or soft tissue imaging if patients with MoM hip implants have none of the signs or symptoms described above and the orthopedic surgeon feels the hip is functioning properly.
The FDA recommends that asymptomatic patients with MoM hip implants continue to follow-up with their orthopedic surgeon every 1 to 2 years to monitor for early signs of change in hip status. These periodic follow-ups of asymptomatic patients with metal-on-metal hip implants, should include physical examinations and routine radiographs. If the hip is functioning properly, the FDA does not believe there is a clear need to routinely perform additional soft tissue imaging or assess metal ion levels in the blood.
The FDA recommends that orthopedic surgeons select a metal-on-metal hip implant for their patients only after determining that the benefit-risk profile of using a metal-on-metal hip implant outweighs that of using an alternative hip system (metal-on-polyethylene, ceramic-on-polyethylene, ceramic-on-ceramic or ceramic-on-metal). Factors to consider include the patient’s age, sex, weight, diagnosis, and activity level. A 2012 FDA advisory panel of experts identified young males with larger femoral heads as the best candidates for hip resurfacing systems.
Additionally doctors should inform patients about the benefits and risks of metal-on-metal hip implants, including the risk that the hip implant may need to be replaced. They should also discuss the patient’s expectations and review the potential complications of surgery with a metal-on-metal hip implant.
Orthopedic surgeons need to pay close attention to patient populations for which metal-on-metal hip systems are contraindicated and be aware of the risk factors that may predispose a device to excess wear and early failure. There are certain patients who are at risk for increased device wear and/or adverse local tissue reactions (ALTR) and should be followed more closely. They may include:
- Patients with bilateral implants
- Patients with resurfacing systems with small femoral heads (44mm or smaller)
- Female patients
- Patients receiving high doses of corticosteroids
- Patients with evidence of renal insufficiency
- Patients with suppressed immune systems
- Patients with suboptimal alignment of device components
- Patients with suspected metal sensitivity (e.g. cobalt, chromium, nickel)
- Patients who are severely overweight
- Patients with high levels of physical activity.
Doctors should conduct a thorough evaluation if a patient with a metal-on-metal hip experiences local symptoms such as pain or swelling at or near the hip, a change in walking ability or a noise from the hip joint more than three months after metal-on-metal hip implant surgery.
Doctors should follow symptomatic patients with metal-on-metal hip implants at least every six months. For some symptomatic patients with metal-on-metal hip implants, additional diagnostic imaging is required to assess and diagnose soft tissue findings surrounding the implant. If the doctor determines that an MRI of a metal-on-metal hip implant patient is appropriate, the FDA recommends the following:
- Consult with the radiologist to evaluate the benefits and risks of utilizing MRI with metal artifact reduction;
- Review the available device-specific labeling from manufacturers for MRI Conditions; and
- Inform the MRI site that the patient has a metal-on-metal hip implant.
Several factors can impact the accuracy, reproducibility, and clinical interpretation of metal ion test results. The FDA does not believe there is a clear need to routinely check metal ion levels in the blood if the orthopedic surgeon feels the hip is functioning properly and the patient is asymptomatic. Patients with metal-on-metal hip implants who develop any symptoms or physical findings that indicate their device may not be functioning properly should be considered for metal ion testing.
A doctor measuring metal ions, should consider obtaining and following serial measurements (using the same sample type, the same measurement method, and preferably the same laboratory) in determining metal ion levels in symptomatic patients. At this time, the FDA is not recommending a specific metal ion level as a trigger for revision or other medical intervention. The metal ion concentration values, including increases in metal ion levels over time, should be considered in addition to the overall clinical scenario including symptoms, physical findings, and other diagnostic results when determining further actions. Currently, the most reliable test results are available for cobalt in EDTA-anticoagulated blood. For chromium testing, a validated method that resolves potential interferences must be used.
The decision to revise a metal-on-metal hip implant should be made in response to the overall clinical scenario. In case of adverse local tissue reactions (ALTR), revision of a metal-on-metal hip implant may have a worse prognosis than revision of other types of bearing surfaces.
In selecting components for revision:
- Consider the benefits and risks of all bearing surfaces for each patient.
- Check the specific device labeling for compatibility of device components.
- If a patient is suspected to have developed metal sensitivity, carefully select the materials of the revision components (potentially avoiding materials with nickel or chromium).
See the FDA Safety Communication
See a related FDA Safety Communication
See the FDA Metal-on-Metal Hip Implant Webpage