Finite element simulation of humeral intramedullary nailing: the case of torsion loading
Virginie Astier,1, 2, * Pierre-Jean Arnoux,1 Lionel Thollon,1 Frédéric Mouret2 and Christian Brunet1
1 Laboratoire de Biomécanique Appliquée (LBA), UMRT24, INRETS & Université de la Méditerranée (Faculté Médecine Secteur Nord), 13916 Marseille, France
2 PROTOMED, Faculté de Médecine Secteur Nord, 13916 Marseille, France
Humerus midshaft fractures may lead to non-union or other complications. Current surgical techniques (nail, plate, external fixator, immobilization) are not considered optimal. Yet the intramedullary nail offers many advantages (haematoma preservation, early mobilization) and is commonly employed. Understanding the failure mechanisms of an intramedullary nail is complex. A finite element (FE) model of the humerus was used in order to compare the biomechanical behaviours of intact and implanted bones. The FE model allows local stress to be estimated (not available from in vitro experimentation), provides understanding of the nail–bone interaction and the bone rehabilitation process and finally allows the consequences of retaining the nail after total bone healing to be investigated. The humerus model was built from a computer tomography (CT) scan and a standard nail design was introduced into the bone. Models were then loaded in torsion to compare intact bone and intramedullary fixed bone. Several stages of the healing process were simulated and bones were stressed to failure. The results showed relevant failure processes on intact bone with failure profile and force level similar to biomechanical and clinical data. Nailed bone results were also compared with experimental studies. Simulation revealed local damage effects at the bone–nail interface that were coherent with clinically observed complications.
Keywords: finite element model, healing process, humerus shaft fracture, intramedullary nail, torsion test