What is my implant made out of?

Patients often ask what their implants are made of. The answer depends on many things including if the patient had a total hip replacement or a total knee replacement.

Total hip replacements usually are made of a titanium alloy. The total hip replacement consists of a stem that goes into the femur and a cup that is impacted into the hip socket. Both of these materials are made of titanium with smaller amounts of other metals. 

The bearing surface of the hip replacement can vary based on patient and surgical factors. The ball on the femoral stem (in the ball-in-socket joint) can be composed of either ceramic or cobalt chrome. There has been a push to ceramic recently as this has better long-term wear characteristics. The socket also has a bearing surface. The socket can be lined with either high molecular weight polyethylene or ceramic. Most surgeons use the polyethylene, which is in essence extremely hard and durable plastic. 

Knee replacements are similar, but different. This has to do with the forces that distribute across the hip and the knee. The knee experiences a vareity of forces like sliding or sheer, whereas the hip has a fairly constant vector of force. 

Knee replacements are composed of the tibial implant, the femoral implant and a bearing surface in the middle. For the most part, the femoral implant is composed of coblat chromium and the tibial implant is titanium. Knee replacements also have a bearing surface, or a "shim" to help get ligament tension correct. This shim is composed of high molecular weight polyethylene. 

There are other variations to this include ceramic knees or the entire tibial component of a knee replacement composed of polyethylene.  For the most part though, the description above is what makes up most hip and knee replacements.