Paper focuses on biomechanics, specifically on locking cortical bone screws in angularly stable plates used for the treatment of bone fractures in the medical fields of traumatology and orthopaedics. During extraction of titanium-alloy implants, problems are encountered in an effort to loosen some locking bone screws from the locking holes of an angularly stable plate and the subsequent stripping of the internal hexagon of the screw head. The self-locking of the screw-plate threaded joint was verified by calculation and the effect of the angle of the thread on the head of the locking cortical bone screw on self-locking was evaluated. The magnitude of the torque, causing the stripping of the internal hexagon (the Inbus type head) of a locking cortical bone screw with a shank diameter of 3.5 mm from Ti6Al4 V titanium alloy to ISO 5832-3, was determined experimentally. Also, it was experimentally found that the rotation of the screwdriver end with a hexagonal tip inside the locking cortical bone screw head during stripping of the internal hexagon causes strain of the screw head perimeter and thereby an increase of thread friction. The effect of tightening torque on the possibility of loosening of the locking cortical bone screw from the locking hole of an angularly stable plate was assessed experimentally. From the evaluation of five alternative shapes of locking cortical bone screw heads in terms of the acting stress and generated strains, it follows that the best screw is the screw with the Torx type head, which demonstrates the lowest values of reduced stress and equivalent plastic strain. Based on experiments and simulations the authors recommend that all global producers of locking cortical bone screws for locking holes of angularly stable plates use the Torx type heads, and not heads of the Inbus type or the Square, PH, PZ types.

The presented article investigates the biomechanics of the calcaneal nail C-NAILTM by numerical calculations and, partially, experimentally. This nail is widely used in trauma and orthopaedics. A numerical model of implants directly interacting with the bone tissue model obtained from CT scans was calculated. The material properties of the bone tissue can be described by several models; in this work, a non-homogeneous material model with isotropic elements and prescribed elastic modulus was used to provide a more accurate model of the applied force distribution on the individual parts of the implants. The critical areas of the nail and its fixtures were investigated using finite element strength calculations to verify their strength and reliability, contributing to the safety and faster and easier treatment of patients. These analyses suggest that the strength of the calcaneal nail C-NAIL, as well as the stabilization of bone fragments resulting from its use, are sufficient for clinical practice.

This article deals with the strength analysis of an intramedullary nail (internal fixator), used in traumatology/orthopaedic for a broken heel bone (calcaneus). The application focuses on the unique miniinvasive C-NAIL produced by the company Medin a.s. (Nové město na Moravě, Czech Republic). The focus is on types of calcaneal fractures and the possibilities of treating them, on the analysis of calcaneus load and the creation of a CAD-FEM model of the calcaneus from CT images (design -the engineeering point of view). Consequently, an analysis is carried out of the peripheral conditions including loading. The calculations were done on solid ("healthy") bones and bones cut into indidivual bone fragments (imitating broken bones), using the finite element method in the Ansys Workbench application.

There are many ways for osteosynthetical treatment of broken bones via fixation. One of them is internal fixation by headless screw, which causes desired compression of bone fragments. In cooperation with medics and industry, FEM simulation (i.e. stress, deformation) was done for prototype of headless screw for 5th metatarsus. Simulations were based on experiment and are followed by other simulation methods too. The aim of this research is to describe basis of issue, define mechanical dependences in headless screws and assessment of headless screws. According to the results, the headless screws can be applied in orthopaedics treatment of fractures.