Metal on Metal Hip Implants
The hip replacement prosthesis consists of two basic components: the socket and the ball (usually attached to a stem that is impacted into the thigh bone)
These components can be constructed of various types of materials. These materials can be the same or different.
Metal on metal replacement, both for total hips and resurfacing hip procedures consists of a metallic ball articulating with a metal socket. They have been shown to be more durable and potentially last longer than many other implants. Also the ball is typically larger providing increased ROM for activities with much improved stability (decreased dislocation risk). Thus they may be advantageous for younger more active individuals with higher functional demands.
The most important fact, is that the vast majority of patients with these implants have had NO major problems
However, recent information about the wear of certain metal-on-metal devices have raised concerns about their use
When there are problems with these implants, they typically produce increased wear debris, (metal ions secondary to corrosion) which may cause a local soft tissue reaction with pain and swelling, and occasionally loosening of the total hip components. Very rarely, symptoms elsewhere in the body can occur from metal ions in the blood stream.
What is the problem? No one can say with 100% certainty but there are basically 3 areas of concern
- Certain implant designs have been shown to have increased problems and have been withdrawn from the market
- Alignment of the total hip components is important, especially the socket. With a larger metal ball and increased ROM, impingement of components can occur. (e.g. when the shoulder of the femoral stem rubs against the socket, rather than the ball)
- Allergic and hypersensitivity reactions to the metal, implant rejection These are rare
We certainly discuss all of these concerns and joint replacement options prior to any surgical procedure
The FDA statements on these devices can be accessed at: www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/MetalonMetalhipImplants.