A long-term clinical study of 41 Flatt metallic hinged prostheses inserted in the metacarpophalangeal joints of ten rheumatoid patients was completed to provide a historic and clinical perspective of the ongoing clinical performance of this prosthesis. Postsurgical analysis performed an average of 138 months after operation demonstrated an average active range of metacarpophalangeal joint motion of 24 degrees, with average maximum active extension of 16 degrees and flexion of 40 degrees. Motion through this device in the metacarpophalangeal joint was relatively well preserved with time and was within a functional range. Recurrent digital ulnar deviation was observed in 58% of patients, digital malrotation in 50%, and extensor tendon redislocation in 45%. The prosthesis failed by screw or prong failure (47%). Periprosthetic radiolucency was common (87%), indicating poor host bone tolerance. With net bone resorption the prosthesis migrated, often perforating the cortex of the metacarpal (44%) or proximal phalanx (59%). Patient satisfaction, despite suboptimal clinical results, was high. All patients considered the appearance of the operated hand and pain relief improved. These advantages must be considered relative to the disadvantages of recurrent digital deformity, poor host tolerance, and unpredictability of clinical results.