Biomechanical testing of a new plate system for the distal humerus compared to two well-established implants

Purpose: A biomechanical study was performed to test the hypothesis that a new anatomically preformed, thinner, soft-tissue protecting plate system for distal humeral fractures (Tifix®-hybridplate [HP]) would show comparable results in the quasi-static and dynamic testings compared to two conventional implants: The 3.5-mm reconstruction plate (RP) providing primary stability with normal bone mineral density (BMD), and a multidirectional locking plate (Tifix®-plate [P]) which can be used with poor bone quality. Methods: The Tifix®-HP was developed by the working group. The biomechanical testing was performed on a C2-fracture-model in 24 synthetic humeri. Three groups, each with eight bone-implant-constructs, were analysed in quasi-static and dynamic tests. Results: The quasi-static measurements showed that under extension loading both locking plates (Tifix®-P, Tifix®-HP) were significantly stiffer than the reconstruction plate, and that the Tifix®-HP had a significantly lower stiffness than the two other implants under flexion loading. In the dynamic tests the Tifix®-P allowed significantly less fracture motion compared to the Tifix®-HP and the reconstruction plate. In an osteopaenic bone model locking plates failed only under much higher dynamic force than the reconstruction plate. The reconstruction plate and the Tifix®-P always failed through screw loosening, whereas the newly developed Tifix®-HP showed screw loosening in only one third of cases. Conclusion: The hypothesis that the newly designed plate system showed comparable results in the quasi-static and dynamic tests compared to the conventional implants with a significantly lower implant volume and thickness was confirmed.