A biomechanical analysis of intramedullary nailing for humeral shaft fractures using 3D-finite element method

Mun-Sik Ko, Gyong-Ryol Kang, Ju-Song Kim, Ho-Nam Pak, Gwang-Rim Choe, Jin-Myong Ra


Background: Intramedullary nailing by antegrade and retrograde technique was introduced in humeral shaft fractures after interlocking nailing of femoral and tibial fractures achieved excellent results. The aim of this study was to evaluate biomechanical properties of antegrade and retrograde nailing in diaphyseal fractures according to levels of the humerus.
Methods: To estimate and compare biomechanical stability of antegrade and retrograde nailing, 3D geometrical and finite element method (FEM) models of the humeral fractures and intramedullary nails were formed using Solidworks software, based on CT scans of the humerus and analyzed with ANSYS 15.0 program. Biomechanical analysis was performed under three types of loads: anterior-posterior (AP) bending, torsion and axial compression.
Results: The bending properties of antegrade nailing were higher than those of retrograde nailing in any site of the humeral shaft fractures. During the testing under torsion, antegrade nailing showed that the displacements of fracture sites were lower compared to those retrograde nailing in the proximal and distal diaphyseal fractures. Under axial compression, antegrade intramedullary nailing demonstrated that the stiffness and displacement were found to be lower than those by retrograde nailing in the distal shaft of the humerus and there were no significant differences in stiffness and displacement between antegrade and retrograde nailing in the proximal diaphyseal and midshaft fractures.
Conclusions: For the proximal and distal shaft fractures of the humerus, the stability of antegrade nailing was higher than the stability of retrograde nailing. In the midshaft fractures of the humerus, there was no biomechanical difference between antegrade and retrograde technique.