Silastic metacarpophalangeal joint arthroplasty

Abstract

Of all the joints of the hand arthroplasty of the metacarpophalangeal joint of the fingers has been most widely undertaken and probably the most successful procedure. The success is in no small matter due to the success of silicone hinged implants at this site, combined with this joints frequent involvement in patients with rheumatoid arthritis. As a consequence the replacement of this joint in this group of patients has become the operation of choice, with long term benefits reported over many years. In 1968 Swanson and Niebauer reported the use of a silicone rubber spacer metacarpophalangeal joint replacement (Fig. 1). At that time they reported good to excellent short term results, which have ultimately been reproduced throughout the world. From that time there have been a number of further developments of this type of implant with an improvement in the materials used, and also the design. The use of this type of silicone-based implant has been so successful that it is now hard to envisage that any hand surgery unit does not use this type of implant on a routine basis. As stated previously the indication par excellence for arthroplasty of the metacarpophalangeal joint is inflammatory arthritis, particularly rheumatoid arthritis and it is in this situation that the hinged silastic implant has been proved to be ideal. For other indications however, particularly trauma or osteoarthritis, silastic has been less successful, the principal reason being that in the otherwise normal hand the forces applied to the implant quite quickly result in failure of the silastic. As a consequence of this newer two-part prosthesis has been developed that is often made of titanium or cobalt chrome with high density polyethylene, the designs often mimicking normal anatomy. More recently a newer material, pyro-carbon, has become available. With these new implants, however, have come changes in surgical technique. For the silastic implants essentially the procedure is one of an excision arthroplasty with the silastic acting as an internal splint, allowing the soft tissues to rebalance. Plainly this is not the case with the two-part implants and as such greater care has to be taken with regard to bone resection and realignment as instability can be a significant problem.