What is my hip or knee implant made of?

Many people have questions about implant materials.  This is especially important in light of past problems with certain types of metal implants.

It is important first of all to distinguish between the implants themselves and the bearing surface.  The bearing surface is the part of the hip or knee implant that moves against other parts of the implant.

In hip replacement, most of the implants which are inserted against the bone, and have bone grow on to them, are made from titanium.  Occasionally, an alloy of cobalt and chromium is used.  These metals of the hip stem and socket are separated from contact with each other by the bearing surface.  Typically, the bearing surface consists of a ceramic ball and a polyethylene liner.  In this fashion, metals do not contact each other, and the concern for metallosis (metal ions getting into tissue or blood) is significantly lower. 

In the past, metal balls and sockets were sometimes used, coming into contact with each other as a bearing surface.  Some of these designs did very well, but others did lead to metal problems.  These types of bearings are used rarely today.

In knee replacement, most systems use a cobalt and chromium alloy for the femur (upper part) and titanium for the tibia (lower part).  These metals are separated by a piece of polyethylene which sits into the lower titanium implant.  In this fashion, metals do not contact each other.

New Joint Commission regulations encourage patients to have implant discussions with their surgeons.  We are happy to provide you with any information that you would like about your specific implant.