Metacarpophalangeal Joint Implants: II. Roentgenographic Study of the Niebauer™ Cutter Metacarpophalangeal Joint Prosthesis

Abstract

A roentgenographic study was carried out on 41 Niebauer^T-^MCutter Metacarpophalangeal Joint Prosthesis from 1 to 36 month; postoperatively, a total of 105 examinations. The examinations were performed in the AP-projection and in the lateral projection by tomography in maximum active extension and flexion. The tomographic examinations revealed implant damage of three kinds: cracking within the midsection; fragmentation of the midsection; fracture of the hinge. Cracking within the midsection was found in 8 implants between 6 and 12 months postoperatively and in 1 implant later than 12 months. Later examinations revealed fragmentation of the midsection in 2 implants previously showing cracks. Hinge fracture was observed in 22 implants. Implant damage was found in a total frequency of 26/41. Bone reaction was found on the tomograms in all the operated joints, and could not be evaluated on the AP-projections. A bony spur was found to develop on the metacarpal bone volarly at the site of the osteotomy in 35 joints. In 2 of these the bony spur reached the base of the proximal phalanx, causing anchylosis. Bone resorption was found in 23 joints, constantly dorsally in the metacarpal bone and volarly in the proximal phalanx. The mechanism of the implant damage is discussed with respect to the shearing forces in the joint and the two materials of differing elasticity constituting the implant. The bone reaction is discussed with respect to the intended fixation of the intramedullary stems.