Anatomical plate configuration affects mechanical performance in distal humerus fractures.

BACKGROUND Because of strong loads acting in the elbow joint, intraarticular fractures with a methaphyseal comminuted fracture site at the distal humerus demand a lot from the osteosynthetic care. Ambiguities arise concerning to the anatomic position of the implants and the resulting mechanic performance. The aim of this biomechanical study was to compare the performance of different anatomical plate configurations for fixation of comminuted distal humerus fractures within one system. METHODS In an artificial bone model two perpendicular and one parallel plating configuration of a dedicated elbow plating system were compared with respect to system rigidity (flexion and extension) and dynamic median fatigue limit (extension). The flexion tests were conducted under 75° and the extension tests under 5°. Furthermore, the relative displacements were recorded. As a fracture model an AO C 2.3-fracture on an artificial bone (4th Gen. Sawbone) was simulated via double osteotomy in sagittal and transversal plane. FINDINGS Large differences in mechanical performance were observed between flexion and extension loading modes. In extension the parallel configuration with lateral and medial plates achieved the highest bending stiffness and median fatigue limit. In flexion the highest bending stiffness was reached by the construct with a medial and a postero-lateral plate. Failure of the implant system predominantly occurred at the screw-bone interface or by fatigue of the plate around the screw holes. INTERPRETATION All three plate configurations provided sufficient mechanical stability to allow early postoperative rehabilitation with a reduced loading protocol. Although the individual fracture pattern determines the choice of plate configuration, the parallel configuration with lateral and medial plates revealed biomechanical advantages in extension only.