This article represents a multidisciplinary approach to biomechanics (engineering + medicine) in the field of “collum femoris” fractures. One possible treatment method for femoral neck fractures, especially for young people, is the application of cancellous (i.e. lag or femoral) screws (with full or cannulated cross-section) made of Ti6Al4V or stainless steel. This paper therefore aims to offer our own numerical model of cancellous screws together with an assessment of them. The new, simple numerical model presented here is derived together with inputs and boundary conditions and is characterized by rapid solution. The model is based on the theory of beams on an elastic foundation and on 2nd order theory (set of three differential 4th order equations, combination of pressure and bending stress-deformation states). It presents the process for calculating displacements, slopes, bending moments, stresses etc. Two examples (i.e. combinations of cancellous screws with full or cannulated cross-section made of stainless steel or Ti6Al4V material) are presented and evaluated (i.e. their displacement, slopes, bending moments, normal forces, shearing forces and stresses). Future developments and other applications are also proposed and mentioned.

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.

This article deals with strength and stiffness analysis of headless screw. This issue was solved in cooperation with engineering industry and doctors. The problem was solved using a stochastic approach, which utilizes the field of random events (simulations), which are applied for determination of input values. The prototype of headless (Herbert) screw Ti4.0/1.4x30/75 was used for solving this problem. Mathematical equations for analytical calculation of the maximal equivalent stress in screw were established. This issue is statically indeterminate problem in compressive and tensile stresses and needs one more equation (i.e. the condition of deformation), which describes relationship between extension of screw and contraction of bone. Resulting values are not defined for one specific model, but the simulation is taking into account a large amount of random samples (specifically 5×10 6 random simulations), which are distributed by bounded histograms. Furthermore, the probabilistic functions of simulated screw were determined. Due to stochastic strength analysis of headless screw, it meets reliability conditions for practical application in osteosynthetic treatment, see [Frydrysek 2016]

BackgroundTraumatic hemorrhagic shock resulting in tissue hypoxia is a significant cause of morbidity and mortality in polytraumatized patients. Early identification of tissue hypoxia is possible with microdialysis. The aim of this study was to determine the correlation between a marker of tissue hypoxia (L/P; lactate to pyruvate ratio) and selected parameters of systemic oxygen delivery (Hb; hemoglobin) and oxygen extraction (ScvO2; central venous oxygen saturation). We also investigated the severity of tissue hypoxia over the course of care.MethodsAdult patients with traumatic hemorrhagic shock were enrolled in this prospective, observational study. Microdialysis of the peripheral muscle tissue was performed. Demographic data and timeline of care were collected. Tissue lactate, pyruvate, glycerol, glucose levels, hemoglobin, serum lactate and oxygen saturation of the central venous blood (ScvO2) levels were also measured.ResultsThe L/P ratio trend may react to changes in systemic hemoglobin levels with a delay of 7 to 10 hours, particularly when systemic hemoglobin levels are increased by transfusion. Decrease in tissue L/P ratio may react to increase in ScvO2 with a delay of up to 10 hours, and such a decrease may signify elimination of tissue hypoxia after transfusion. We also observed changes in the L/P trend in the 13 hours preceding a change in the hemoglobin level. Fluid administration, which is routinely used as a first-line treatment of hypovolemic shock, can cause hemodilution and decreased hemoglobin. When ScvO2 decreases, increase in L/P ratio may precede the ScvO2 trend by 10 or 11 hours. An increase in the L/P ratio is an early warning sign of insufficient tissue oxygenation and should lead to intensive observation of hemoglobin levels, ScvO2 and other hemodynamic parameters. Patients who were treated more rapidly had lower maximal L/P values and a lower degree of tissue ischemia.ConclusionThe L/P ratio is useful to identify tissue ischemia and can estimate the effectiveness of fluid resuscitation. An increase in the L/P ratio is an early warning sign of inadequate tissue oxygenation and should lead to more detailed hemodynamic and laboratory monitoring. This information cannot usually be obtained from global markers.