Materials Used in Orthopaedic Implants

Physical Characteristics—Material Resistance to Wear and Corrosion and Biocompatibility

Resistance to Wear

Some of the parts that make up an orthopaedic implant must touch each other or rub together, especially in the case of an artificial joint. Any time two parts rub together, friction is created and the parts may possibly wear over time. When an implant wears, tiny particles of the material are removed from the surface and remain in the tissues that surround the implant. In some patients, these particles may cause a reaction that could lead to inflammation. If the inflammation is severe, or continues for too long, the implant may become loose.

Generally, the harder the material, the more resistant it is to wear. Also, the choice of the two materials that rub together in an implant is important in minimizing wear. Many combinations of materials are used today for implants, including metal on polyethylene, metal on metal, ceramic on ceramic, and ceramic on polyethylene.

Resistance to Corrosion

Some of the normal chemicals that make up the fluids in your body can damage certain materials. Corrosion occurs as these chemicals react with the implant material, creating particles similar to small wear particles. Not only can corrosion weaken the implant, but the particles produced can remain in the tissues that surround the implant. This could eventually lead to implant failure or, in severe cases, damage to the bone.

Biocompatibility

Biocompatibility refers to the way materials interact with your body. Some materials, lead and mercury for example, are naturally harmful when taken into the body, so are not suitable for implanting. Other materials are not suitable to implant because the body fluids cause them to break down, either weakening them, or causing corrosion or other byproducts. Some materials may cause irritation or, rarely, may cause an allergic reaction. If this happens, the implant site may experience some inflammation which may involve swelling, redness and pain. Fortunately, all biomaterials used in medical devices, in the U.S. and in most other countries, must be extensively tested for biocompatibility before they are approved for use.

Because some few people may have an allergic reaction, even to materials that are generally safe for the general public, it is important to tell your doctor about any allergies you may have.