[The aetiology of arthrosis of the first metacarpophalangeal joint and its treatment with joint-replacement (author's transl)].

The first metacarpo-phalangeal joint is assumed to be exposed to incongruent functional demands, when gripping. They may lead to pre-arthrotic deformity and frequent arthrosis. A new special prosthesis, its insertion and first results are described. It fulfills all functional demands and can be used also for younger patients.