Die in-vitro-stabilität des langfingergrundgelenkes nach endoprothetischer versorgung mit silastik-implantaten (sutter) und oberflächenersatz (avanta)

Objective: The requirements for metacarpophalangeal prosthesis are high. Ideally it should fulfil the criteria of strength, adequate mobility, absence of pain and stability, which, however, have to date been reached over the long term with one surface replacement implant made of pyrocarbon. The purpose of this study was to examine the stability of a silastic interposition implant (Sutter) and a surface replacement implant (Avanta, Mayo-current) in comparison with an intact metacarpophalangeal joint (MCP) in eight hand specimens. Material and Methods: Eight fresh-frozen normal human cadaveric hands were used to compare the kinematics of MCP using the magnetic Isotrak system (Polhemus Navigational Systems, Colchester, VT). The lateral and rotational stability of the MCP joint were determined after implantation of the two prostheses, after dissection of the collateral ligament and subsequent reconstruction, followed by dissection of the collateral ligament and reconstruction of the extensor tendon apparatus. Results: The stability of the MCP joint after Sutter and Avanta replacements was similar to that of the normal joint. The maximum angular displacement was 39 (Sutter) and 43 (Avanta) degrees for lateral deviation and 22 (Sutter) and 37 (Avanta) degrees for rotation during the passive flexion and extension motion. A significant difference regarding stability was generally found between the intact and the implanted specimens.There was no significant difference noted between the intact situation and the reconstruction of the extensor apparatus. Conclusions: The results suggest that the collateral ligament is of essential importance for the stability of the MCP joint. Its preservation or reconstruction, which is rather difficult in the rheumatoid hand, enables flexion and stability that are approximately the same as those of an intact joint. Due to the attachment of the extensorhood to sagittal bands that lifts the proximal phalanx and provides stability a reconstruction of the extensor apparatus most closely matched the stability of the intact joint. However, collaterals are generally more essential with respect to stability. By using new materials and taking the anatomic and biomechanical requirements into consideration, the endoprosthesis of the finger joints has created an option to achieve good long-term results. The inadequate results of earlier and current prostheses are a consequence of their mechanical construction and their materials. The success of the new implants needs to be proven by preferably long-term, controlled studies with a longer period of observation.