Pushout strength of tibial locking screws: Development of finite element models

This study investigated the bone holding power of tibial locking screws by mechanical testing and finite element analysis. In mechanical tests, five types of commercially available tibial locking screws: Howmedica, Osteo AG, Richards type I, Richards type II, and Synthes were inserted in a cylinder of polyurethane foam bone. Axial load was applied to the screw tip to push the screws out of the foam bone by a material testing machine. The pushout strength of each screw was recorded. In finite element analysis, three-dimensional finite element models with nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The results showed that the order of the pushout strength of the locking screws from high to low was Osteo AG, Richards type II, Richards type I, Howmedica, and Synthes. The results of mechanical tests were highly correlated to the results of finite element analysis. Finite element models with low elastic modulus of bone and no frictional force between the screws and bones can better simulate the situations of mechanical testing. The finite element models built in this study may help the manufacturers evaluate new designs of locking screws before manufacture and assist surgeons to select suitable devices for their patients.