Metacarpophalangeal joint replacement with osseointegrated endoprostheses.

A new type of endoprosthesis for reconstruction of the metacarpophalangeal (MCP) joint has been tested. The novel arthroplasty consists of a joint mechanism with two screw-shaped fixtures for bone anchorage. These fixtures, of commercially pure titanium, are gently screwed into the anchoring bone on each side of the diseased joint, the aim being to achieve osseointegration, i.e. a direct contact between implant and bone without interposed soft tissue layers. The hand was immobilized in a dorsal splint for 8-10 days post-operatively after which a carefully controlled mobilization program was initiated. In principle, the titanium fixtures, the surgical technique and the primary immobilization represent an approach similar to that previously used in various reconstruction procedures of the jaw. This paper describes 5 case histories of reconstructions required because of osteoarthrosis in a single MCP joint. Prior to the operation, all patients suffered from severe problems resulting from their arthrotic joints and they had not been able to work for several months. After surgery they were evaluated by a clinical assessment program and X-rays were taken at various times of follow-up. As well as visual inspection all radiograms were subjected to densitometry by means of a computer-based image-analysis system in order to provide information on the development of bone density in the bone-to implant interface region. From a functional point of view the treatment with osseointegrated prostheses must be regarded as being successful. All patients were able to go back to their original work and their hands had a satisfactory range of movement and grip strength with no signs of impaired function on longer follow-up time. Clinical problems were one re-operation, one case of implant fracture and one case requiring exchange of the joint mechanism. The computer-assisted evaluation of the radiograms revealed the presence of calcified tissue in many sections where the naked eye was not capable of differentiating any bone. In conclusion, it seems possible to establish osseointegration of MCP-endoprostheses in the arthrotic human joint in complicated cases which were regarded as contraindicated for any other joint arthroplasty.