Arthroplasty is the operation for construction of a new movable joint. It is not applicable to every joint: in practice, its use is almost confined to the shoulder, the elbow, the hip, the knee, certain joints in the hand, and the metatarso-phalangeal joints in the foot.
The indications for arthroplasty are not well defined, for there is considerable diversity of opinion among different surgeons. Broadly, it has a use in the following conditions:
Methods of arthroplasty.
Three methods are in general use:
Excision arthroplasty. In this method one or both of the articular ends of the bones are simply excised, so that a gap is created between them (Fig. 13). The gap fills with fibrous tissue, or a pad of muscle or other soft tissue may be sewn in between the bones. By virtue of its flexibility the interposed tissue allows a reasonable range of movement, but the joint often lacks stability. The method is applicable to all the joints for which arthroplasty is practicable except the knee and ankle. It is used most commonly at the metatarso-phalangeal joint of the great toe, in the treatment of hallux valgus and hallux rigidus. At the hip it may be used as a salvage operation after failed replacement arthroplasty.
Three methods of arthroplasty, as exemplified at the hip. Figure I 3 Excision arthroplasty. Note the interposed soft tissue. Figure I 4-Half-joint replacement arthroplasty: the femoral head is replaced by a metal prosthesis. Figure I5 Total replacement arthroplasty. The femoral head is replaced by a metal prosthesis and the acetabulum by a plastic socket. Both are held in place by acrylic filling compound or 'cement'.
Half-joint replacement arthroplasty.
In half-joint replacement arthroplasty one only of the articulating surfaces is removed and replaced by a prosthesis of similar shape. The prosthesis is usually made from metal (as in replacement of the femoral head), occasionally from silicone rubber (as in replacement of A carpal bone); and when appropriate it may be fixed into the recipient bone with acrylic filling compound or cement'. The opposing, normal articulating surface is left undisturbed. The technique has its main application at the hip, where prosthetic replacement of the head and neck of the femur is commonly practised for femoral neck fracture in the elderly (Fig. I 4). It has rather a limited use elsewhere, an example being the replacement of the lunate bone by a silicone-rubber ('Silastic') prosthesis in Kienbock's disease.
Total replacement arthroplasty. In this technique both of the opposed articulating surfaces are excised and replaced by prosthetic components (Fig. I 5). In the larger joints one of the components is normally of metal and the other of high-density polyethylene, and it is usual for both components to be held in place by acrylic 'cement'. In small joints such as the metacarpo-phalangeal joints a flexible one-piece prosthesis made from silicone rubber may be used.
Total replacement arthroplasty has proved very successful at the hip and to a lesser extent at the knee. It has been extended, so far with only moderate success, to many other joints including the shoulder, elbow, ankle, metacarpo-phalangeal joints and metatarso-phalangeal joints. A disadvantage which applies also to half-joint replacement arthroplasty-is that there is a tendency for the prosthesis to work loose after a variable time that cannot be predicted. A well-fitted replacement joint may, however, give good service for many years, especially in the case of the hip.