Finite Element Analysis of the Mechanical Strength of Phalangeal Osteosynthesis Using Kirschner Wires

Background: Kirschner wire (K-wire) fixation is widely used to repair metacarpal and phalangeal fractures. In this study, we simulated K-wire osteosynthesis of a 3-dimensional (3D) phalangeal fracture model and investigated the fixation strength at various K-wire diameters and insertion angles to clarify the optimal K-wire fixation method for phalangeal fractures. Methods: The 3D phalangeal fracture models were created by using computed tomographic (CT) images of the proximal phalanx of the middle finger in five young healthy volunteers and five elderly osteoporotic patients. Two elongated cylinders representing K-wires were inserted according to various cross-pinning methods; the wire diameters were 1.0, 1.2, 1.5 and 1.8 mm, and the wire insertion angles (i.e. the angle between the fracture line and the K-wire) were 30°, 45° and 60°. The mechanical strength of the K-wire fixed fracture model was investigated by using finite element analysis (FEA). Results: The fixation strength increased with increasing wire diameter and insertion angle. Insertion of 1.8-mm wires at 60° achieved the strongest fixation force in this series. Fixation strength was generally stronger in the younger group than the elderly group. Dispersion of stress to cortical bone was a critical factor to increase fixation strength. Conclusions: We developed a 3D phalangeal fracture model into which we inserted K-wires; using FEA, we clarified the optimal crossed K-wire fixation method for phalangeal fractures. Level of Evidence: Level V (Therapeutic).