The patent's inventors are Nevelos, James (Chippenham, GB); Krikler, Steven J. (Coventry, GB); Stachniw, Myron B. (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "Conventional Total Hip Replacement (THR) is a very successful procedure for the treatment of arthritis of the hip, a condition which causes considerable pain and loss of movement. As is well known, the hip is a ball and socket joint which allows the upper leg to move from side to side, back to front, and to rotate. The joint is made up of the head of the femur (the ball) which fits into the acetabulum (the socket). In a healthy hip, both the head of the femur and the acetabulum are covered with cartilage which provides a smooth surface allowing the joint to move freely.
"The earliest Total Hip Replacement (THR) procedure, in 1938, involved an implant in which both surfaces were made from metal and was known as a metal-on-metal bearing. During the 1950's and early 1960's, a number of surgeons developed hip implants using this type of bearing, although many of these designs had a tendency to work loose early on as the techniques used to anchor them to the bone were not very successful. However, the implants that did not loosen early on have generally lasted well.
"In the early 1960's, a British Surgeon, Sir
"The plastic used to form the cup 16 is inert and so is well tolerated by the body. Nevertheless, as the metal ball 10 rubs against the plastic cup 16, tiny particles of the plastic are worn away. This plastic debris causes an irritation. Furthermore, as the particles get between the bone and the artificial joint, this irritation causes surrounding bone to be absorbed by the body, leading to a loosening of the artificial joint. In older people, with a lower activity level, this may not happen for twenty or more years, but in younger, more active patients, this may happen much sooner.
"To overcome these problems in younger, more active patients requiring hip replacement, a different type of implant was needed. In 1991 a procedure for metal-on-metal (MoM) resurfacing of the hip was proposed. This has two major differences from a conventional THR. The first is that both components are made from metal, typically Cobalt Chrome. By eliminating the plastic cup of a conventional THR, and making both parts of the bearing surface of metal, the resurfaced hip is expected to last much longer and therefore to be more suitable for higher demanding patients. The second difference is that the procedure is very bone conserving, since the head of the femur is simply reshaped and 'resurfaced', rather than removed. Accordingly, should the device need replacing at some time in the future, this may provide better options for the surgeon at that time as a conventional THR can then be used.
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