The concept of hip resurfacing as opposed to replacing the joint has been attractive to hip surgeons for a long time. The first attempts at doing so were carried out many years before the advent of hip replacement surgery as we know of it now. The main attraction has been the feeling that the procedure attempted to duplicate nature and that only a little amount of bone had to be removed from the hip joint to accomplish the resurfacing. Whereas in hip replacement systems, the whole of the femoral head (the ball of the upper end of the femur or thigh bone) has to be discarded, the resurfacing enables, as the name would suggest, the placement of a new surface onto the femoral head. Only a minimal amount of bone has to be removed from the femoral head -just the amount necessary to reshape the head and machine it to accept accurate seating of the new surface component. Another advantage with the resurfacing procedure is that the ball used in the system is similar to the natural ball and that in turn confers biomechanical advantages to the hip. The force transmission is advantageous and the range of movement possible is greater than when a smaller ball is used.
Hip resurfacing was first attempted in a big way in the early 1980s in the United States. Unfortunately, the failure rate was extremely high and the procedure was abandoned within a few years. The technique appeared to be good in theory, but it did not work in practice and there seem to have been a number of reasons for the failures. The most important cause of failure appears to have been the thin layer of UHMWP (the plastic liner) used in the system. Surgeons at that time were forced into using the thin layer of UHMWP because they had to work with only a small disparity between the size of the socket implanted and the size of the femoral head. They had no control on the size of the femoral head or "cap" being used as it had to match the natural size of the femoral head. They could not use a very big socket as that would have meant sacrificing a lot of good bone on the acetabular (natural socket of the pelvis) side. Had they been able to use a large socket, then that would have allowed those surgeons to use a thick UHMWP component.
The surgeons in the 80s were not aware of the particular problems associated with the use of thin UHMWP components. We know now that these thin components are very prone to wear and breakdown. The particles produced during the wearing out process provoke a particular type of reaction from the bone around the hip joint not very dissimilar to the bone "dissolving". When the bone weakens in this manner it can no longer support the artificial implant which then loosens.
Interest in the concept of resurfacing was reawakened when surgical experience and advances in materials and metallurgy meant that it was possible to produce joint systems that did away with the intervening layer of UHMWP. These newer systems comprised simply of a metal ball articulating with a metal socket. As the metal socket has considerably greater resistance to wear than the polyethylene, there is no difficulty in using the thin metal shells in resurfacing systems. It was apparent that the original concept of resurfacing might work with the newer materials using modern systems and the higher quality finishes obtainable nowadays for metal on metal couplings.
Much of the credit for the renewal of interest in the newer form of hip resurfacing goes to Mr. D. McMinn and Mr. R. Treacy, Orthopaedic Surgeons in Birmingham who have carried out most of the modern research into this system. That probably explains why one of the commonly used resurfacing joints is known as the Birmingham hip.
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