Osteosynthesis Metal Plate System for Bone Fixation Using Bicortical Screws: Numerical-Experimental Characterization.

Abstract

Simple SummaryThis study addresses an important issue concerning the evaluation of stresses in bone shafts stabilized by osteosynthesis metal plates, following routine surgical procedures to repair severe fractures in bone. It is recognized that bone regeneration following fracture is highly dictated by the stress state in the damaged regions. Since metallic inserts, like plates and screws, are usually employed to assure the stabilization of fractures in bone, it is important to evaluate the effect of those parts on the developed stresses in bone tissue. In the present work fracture was induced in a femoral bone of an animal model, which was suitably stabilized with a dynamic compression plate (DCP) using bicortical screws. This system was submitted to bending to trigger damage in bone tissue in the vicinity of metal inserts. Finite element modelling was then performed to mimic damage initiation and propagation in bone, thus simulating the results observed experimentally. Stress distributions in the vicinity of the screwed regions due to fastening of DCP allowed to identify very significant differences, which can affect bone hilling processes. It can be concluded that the developed procedure may be used to help surgeons to support decisions regarding bone repair using standard DCP.This study reports the numerical and experimental characterization of a standard immobilization system currently being used to treat simple oblique bone fractures of femoral diaphyses. The procedure focuses on the assessment of the mechanical behavior of a bone stabilized with a dynamic compression plate (DCP) in a neutralization function, associated to a lag screw, fastened with surgical screws. The non-linear behavior of cortical bone tissue was revealed through four-point bending tests, from which damage initiation and propagation occurred. Since screw loosening was visible during the loading process, damage parameters were measured experimentally in independent pull-out tests. A realistic numerical model of the DCP-femur setup was constructed, combining the evaluated damage parameters and contact pairs. A mixed-mode (I+II) trapezoidal damage law was employed to mimic the mechanical behavior of both the screw–bone interface and bone fractures. The numerical model replicated the global behavior observed experimentally, which was visible by the initial stiffness and the ability to preview the first loading peak, and bone crack satisfactorily.