Metacarpophalangeal Joint Implants: I. Roentgenographic Study on the Silastic® Finger Joint Implant, Swanson Design

Abstract

A roentgenographic study was carried out on 104 Silastic® Finger Joint Implants, Swanson design. Sixty-two of the implants were examined in the anterio-posterior-projection (AP) from 4 months to 5 1/2 years postoperatively, a total of 116 examinations. Forty-two implants were examined in the AP-projection and in the lateral projection by tomography in maximum active extension and flexion from 9 days to 42 months postoperatively, a total of 110 examinations. Stem fractures were found in 11/104 implants: two of these preceded by a laceration of the implant surface visualized by tomography. Fragmentation of the midsection was found in 14/104 implants. Cortical erosion was seen radially in the phalanx and the metacarpal bone in some joints showing ulnar deviation, predominantly MCP joints II and III. On the tomograms a cortical erosion dorsally in the metacarpal bone could be demonstrated. Particularly around the distal stem was found an intramedullary bone lamella, varying in distance from the stem as well as in density and regularity. Bone resorption was found at the site where the midsection bore on the metacarpal bone and the proximal phalanx, resulting in a migration of the implant in a proximal and/or distal direction. The migration of the implant was evaluated on the tomograms with maximum active extension and classified into 4 Grades. Concomitant with the migration in the proximal direction a bony spur developed volarly at the resected end of the metacarpal bone, also seen in the AP-projection. The degree of maximum joint flexion was measured on the tomograms by drawing a line along the dorsal contour of each bone. In some cases flexion was found to decrease as a consequence of implant migration in the distal direction or the development of a bony spur. In several cases the range of flexion was maintained by gliding of the stems, particularly the distal one.