Revision Surgery
The synovial joints of the body last the lifetime of most individuals. During this period they generally serve the person well, allowing him, or her, to undertake many different activities with relative ease and comfort. During these physical activities the joints, like the rest of the body, sustain various strains and knocks which can damage them to some extent but, being made of living tissue, they have the capacity to heal themselves.
This capacity for repair however is limited and, for a variety of reasons, (which include excessive force, infection, diminished blood supply, inflammation or just an inherited predisposition) the smooth articulating cartilaginous surface of the joint becomes irreparably damaged. When this occurs the bone underneath becomes exposed and hardened, the action of the joint becomes stiff and irregular, and its movement becomes painful for the individual. A joint thus affected is termed 'arthritic' and the result is a marked restriction in the function of both the joint and often the limb..
Over the years, a system of artificial joints has been developed which can replace many of the joints of the body if they become arthritic, and emulate their function to a greater or lesser extent. In doing so these artificial joints (or prostheses) move in the same way as the natural joints and bear the same loads. There are, however, two innate problems with them.
• Not being of living tissue the first problem is for the artificial joint to bond to the living bone in order to transmit the forces passing up or down the limb through the joint. This bonding takes place at the junction of the prosthesis with the bone. A common method of fixing the prosthesis to the bone is to use a 'bone cement'. This 'cement' is inserted in a soft form, just before the prosthesis is introduced, and penetrates the bone substance. After introduction the 'cement' hardens and firmly grips the prosthesis in place. The other method to obtaining a bond between the prosthesis and the bone is to encourage the bone itself to grow onto the surface of the prosthesis. This is achieved by using materials which do not irritate the bone and texturing or coating its surface of the prosthesis in a way which allows the surrounding bone to adhere to it.
• Artificial joints, like natural joints are subject to wear but, unlike natural joints, do not have the capacity to repair themselves. Because of this the artificial joint has a finite lifespan and ultimately will fail. The articulating surfaces may simply wear away or, more commonly, the components loosen from the bone because the bonding breaks down. This loss of bonding arises from either a breakdown of the 'cement' or from a loss of the bone itself, which is often a response to materials released by the mechanical wear. Rarely does the joint fail, these days, as a result of a component breakage.
With these problems in mind, artificial joints are presently constructed with a view not only to obtaining adequate functioning of the joint but also to obtaining as much 'life' from the prosthesis as possible. This is done by addressing those areas where it is known that a prosthesis can fail by improving the strength and wear characteristics of the materials which make up the prostheses, and techniques to improve the bonding of the prosthesis with the bone. Unfortunately even the most durable artificial joint may ultimately fail and, if this occurs, need revision.
The revision operation is much more demanding than that undertaken to insert the primary prosthesis. The individuals are generally older than those undergoing a joint replacement for the first time. As a result they are often suffering from a miscellany of coincidental medical problems. The tissues around the joint are scarred and stiff from the previous surgery. The bone required to support the new prosthesis may be deficient and the bone which is present may be weak. There is a higher incidence of infection with secondary operations. All these measures make a joint revision operation somewhat hazardous for the person undergoing it and much care and thought is required before embarking on such a procedure.
