New Implant Materials

Most people know that the metal used in implants is Titanium. However, pure Titanium is hardly used today. The Titanium used is usually an alloy. By adding different metals into Titanium, an alloy is formed. An alloy is stronger than the pure metal. The first Titanium alloy used in orthopedic implant has the formula of 90% Titanium, 6% Aluminum and 4% Vanadium. This metal is used for making the metal shell of the hip socket.

The femoral stem is also made of a newer Titanium alloy. This alloy contains 80% Titanium, 12% Molybdenum, 6% Zinc and 2% Iron. The reason this alloy is used for making the femoral implant is that it is 25% less stiff than the 90% Titanium, 6% Aluminum and 4% Vanadium but 20% stronger in its strength. The top portion of the femoral stem is also coated with hydroxylapatite, a material similar in chemistry to bone. This allows bonding of the metal implant to bone.

The liner of the socket is made of either plastic or ceramic. The newer plastic liner is made from a highly cross-linked ultra high molecular weight polyethylene. When a plastic liner is used, it is usually used with a highly polished metal ball made of a Cobalt-Chromium alloy that is used for making the turbine blades of jet engines.

The liner can also be a highly polished ceramic one. This is the latest in implant material for total hips. When a ceramic liner is used, it must be used with a highly polished ceramic ball. This combination has the least amount of wear in all the materials used in artificial total hips. Why is wear important, it is like the tires of a car, when the tires get bald, they have to be replaced. In fact, the natural hip also gets bald with use. When the cartilage is worn off, the hip needs to be replaced.

These new materials are intended to provide the patient with a longer service life.