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Metal-on-Metal Hip Implants > Concerns about Metal-on-Metal Hip Implant Systems.

Concerns about Metal-on-Metal Hip Implant Systems

All artificial hip replacement systems have risks related to implant or material wear. Metal-on-metal hip (MoM) replacement systems have unique risks in addition to the general risks of all hip implant systems.

Because the metal ball and the metal cup slide against each other during walking or running, some tiny metal particles may wear off of the device and enter into the space around the implant. Some of the metal ions from the metal implant or from the metal particles may even get into the bloodstream.

Orthopaedic surgeons take several precautions before and during the implantation 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 metal particles.

Different people will react to these metal particles in different ways. At this time, it is not possible to know who will experience a reaction, what type of reaction they might have, when the reaction will occur, or how severe the reaction will be. However, it is known that 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).” Such a reaction may cause the implant to become loose or cause pain. Ultimately this can require a revision surgery where the old device is removed and replaced with another one.

In addition to these reactions to metal near the joint and implant, there are some case reports in the literature of a small number of patients in which high levels of metal ions in the bloodstream may have caused other types of symptoms or illnesses elsewhere in the body, including effects on the heart, nervous system, and thyroid gland.

Patients who have MoM hip implants should be aware of potential symptoms which may occur after surgery and indicate that their device is not functioning properly. Common symptoms may include:

  • Pain in the groin, hip or leg
  • Swelling at or near the hip joint
  • A limp or change in walking ability

There are many reasons why any of these symptoms may arise or worsen after surgery and it does not necessarily mean that a reaction to the metal particles from the device is taking place. A thorough evaluation by an orthopaedic surgeon is needed to determine the actual cause. Besides a physical exam of the hip, the orthopaedic surgeon may consider several tests to evaluate these symptoms including:

  • Special imaging tests
  • Using a needle to remove fluid from around the joint (joint aspiration)
  • Blood tests, including checking levels of metal ions in the blood

Patients who receive a MoM hip implant should also pay close attention to changes in their general health or new symptoms outside their hip including symptoms related to their:

  • Heart (chest pain, shortness of breath)
  • Nerves (numbness, weakness, change in vision or hearing)
  • Thyroid (fatigue, feeling cold, weight gain)
  • Kidney (change in urination habits)

In April 2010, the United Kingdom’s (U.K.) Medicines and Healthcare products Regulatory Agency (MHRA) issued a medical device alert that included specific follow-up recommendations for patients implanted with MoM hip replacements. The recommendations included blood tests and imaging for patients with painful MoM hip implants.

There are several differences between the U.K. and U.S. regulatory systems and some of the U.K. data may not be directly applicable to the experience in the US. For example, some of the devices available in U.K. are not marketed in U.S. Therefore, the frequency of the reactions described above, in the U.S. is unknown. For this reason, FDA is in the process of gathering additional information about adverse events in people with metal-on-metal hip implants.

At the current time, there is no evidence to support the need for checking metal ion levels in the blood or special imaging if patients with MoM hip implants have none of the signs or symptoms described above and the orthopaedic surgeon feels the hip is functioning properly. The FDA is recommending that asymptomatic patients with MoM hip implants continue to follow-up with their orthopaedic surgeon as prescribed.

If patients with MoM hip implants develop any of the symptoms above, it is very important for them to make appointments with their orthopaedic surgeons promptly for further evaluation.

If patients with MoM hip implants develop any new or worsening symptoms outside of their hips, or if they are referred to doctors to evaluate new conditions, they should let the doctors know that they have MoM hips.