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.
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.