The authors studied the characteristics that would be desirable for a metacarpo-phalangeal joint prosthesis to be used in patients with rheumatoid disease. In these patients the severe destruction of the capsulo-ligamentous structures of the joint often makes prosthetic substitution dissatisfactory, particularly for the index finger.

Such a prosthesis should be restricted in its range of motion, actually abolishing any ulnar deviation. Axial rotaion should be coupled to flexion-extension and radial deviation to gain an adequate stress dissipation at the interface. Both distal and proximal stems should be conical, for the best possible distribution of shear stresses at the interface. A flattening surface should accommodate properly the externsor apparatus without interfering with it. The greatest possible congruence should be required for the articulated components.

The rationale of such a design for a rheumatoid patient lies in the fact rheumatoid arthritis is the most important indication for a metacarpo-phalangeal joint arthroplasty, due to the highly incapacitating condition that may ensue. Then, despite limitations required by the proposed design, an improvement in the functional ability of the rheumatoid patient will be obtained.