Current state of total joint replacement.

Abstract

The hip joint was the first to be totally replaced. The procedure was first carried out in Britain by McKee of Norwich, who used a prosthesis of which both the acetabular and femoral compo nents were of cobalt-chrome and were fixed to the skeleton without using polymethylmethacrylate cement. This technique proved unsuccessful-as in the long run has the combination of cobalt chrome against cobalt-chrome. In the late 1960s Charnley introduced the use of polymethylmethacrylate cement to bond prosthetic components to the skeleton. This technique has stood the test of time and is almost universally used as the bonding technique today. Charnley's first total replacement of the hip used stainless steel for the femoral component and teflon for the acetabular component. The wear-rate of Teflon proved un acceptably high, and in 1962 Charnley switched to using ultra high molecular weight polyethylene. This material has proved satisfactory in clinical use, and it is now almost universally used as one of the two components of total joint replacement prostheses. There are currently many slightly different prostheses com posed of an implantable metal alloy for the femoral component and ultra-high molecular weight polyethylene for the acetabulum. The various prostheses and the procedures by which they are inserted have certain advantages and disadvantages, but all of these are relatively minor and do not broadly affect the clinical outcome. The choice between one prosthesis and another and one surgical approach and another is very much a matter of surgical training and habit. Broadly, replacement of the hip should now provide a comfortable, mobile joint on which a patient can carry out all everyday activities including non contact sports, such as golf, without pain. The actual range of movement obtained depends to some extent on the range pre operatively while obviously the patient's exercise capacity depends on various factors other than the affected hip. In the absence of preoperative local infection, almost every hip can be replaced regardless of the nature of the original condition. The only important disadvantage to the currently available prostheses for total hip replacement is that they transgress the general principle of surgery that healthy tissue should not be sacrificed. On the acetabular side this principle is met since relatively little bone from the pelvis has to be removed. On the femoral side, however, the whole of the femoral head and neck are removed, and the prosthesis is attached via an intermedullary stem to the proximal third of the femoral shaft. Attachment in this way means that not only are the head and neck sacrificed, but that the upper third of the femur is prejudiced should the prosthesis become infected or need to be removed for some other reason. In Britain and other countries in the past few years prostheses have been developed that replace the hip to give clinical results that appear similar to those of conventional prostheses but without sacrifice of bone on the femoral side; such prostheses simply resurface the head of the femur. It is as yet too early to say whether they will function as satisfactorily in the long term as do the conventional implants.