The modern total hip replacement was invented
in 1962 by Sir John Charnley,
an orthopedic surgeon working in a small country hospital
in England. His work has been one of the great triumphs
of Twentieth Century surgery. Two revolutionary features
of the Charnley hip replacement were 1) the combination
of metal gliding on plastic, and 2) the use of methacrylate
cement to attach the artificial components to the bone.
A Canadian orthopedic surgeon (Gunston) working with
John Charnley applied the principles of hip replacement
to the knee. His knee replacement was received with some
enthusiasm by many surgeons. Other surgeons quickly began
to work on newer designs for an improved knee replacement.
| The operation
has become fairly routine and is successful
around 96% of the time. |
One of the first American surgeons to perform knee replacement surgery was the professor of orthopedic surgery at UCLA, Charles Bechtol. His knee replacement was widely used around the world. Dr. Huddleston studied hip and knee surgery with him for a year, and the two later became partners in the first private practice in Los Angeles restricted to hip and knee surgery. When Bechtol retired Dr. Huddleston took over the practice, which he later merged into the Southern California Orthopedic Institute.
The biggest challenge with a joint replacement is making it last a lifetime. A good knee replacement can be expected last longer than a good hip replacement. The emphasis is on the word “good”. The knee is far more complicated than the hip, and a knee replacement operation is way more complicated than a hip replacement. There are ten times more steps in performing a knee replacement compared to a hip replacement, and every detail of the operation has to be near perfect for the new knee to have good motion, and have a chance to last a lifetime.
The term “knee replacement” sounds like a more
radical procedure than it actually is. Most patients
imagine that 3 inches of bone is removed from each
of the knee bones and that a large metal and plastic
device is installed in its place. In actual fact,
the procedure is more akin to dentistry and a better
term would be Knee Resurfacing. A thin layer
of bone is removed from the damaged surface of the
femur (thigh bone) using special instruments which
remove the correct thickness of bone. The removed
bone is then replaced by a thin layer of metal, approximately
the same thickness as the bone which was removed.
In a similar fashion the upper end of the tibia (shin
bone) is removed and replaced with a thin sandwich of metal and plastic. The back part of the knee cap (patella)
is also be resurfaced with a wafer of plastic.
| The
three parts are attached to the bone by means
of a “bone cement” (methylmethacrylate).
When this cement is first mixed it develops a
dough-like consistency. This dough is pressed
into the bone and the parts of the Prosthesis
are pressed into the dough. The cement then hardens
over 10 to 15 minutes into a plastic-like consistency.
After the knee has been replaced, the metal “cap” covering
the end of the femur rubs against the plastic
covering on the end of the tibia, preventing
bone from rubbing on bone and giving relief from
pain. The plastic is high density polyethylene a
material which has a very low wear-rate and a
very low frictional resistance when rubbing against
the highly polished metal surface. |
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