Janoš Kodvanj

Comparative study of three models of extra-articular distal humerus fracture osteosynthesis using the finite element method on an osteoporotic computational model

INTRODUCTION The biomechanical properties of extra-articular fractures of the distal humerus have not been researched sufficiently. The aim of the study was to examine three different models of osteosynthesis for extra-articular distal humerus fractures. Osteosynthesis with two parallel or perpendicular plates is a common method of osteosynthesis for those fractures. We wanted to examine the biomechanical performance of a newly designed Y plate, and compare it to the previously used osteosynthesis methods. MATERIALS AND METHODS On an osteoporotic computational model of the distal humerus, a 10 mm gap was made, 25 mm above the olecranon fossa, and osteosynthesis was performed with the newly designed Y-shaped plate and with 3.5 reconstruction plates in parallel and perpendicular configuration. The numerical simulations in axial compression, bending and varus loading were conducted using the finite element method. RESULTS On all models the largest displacements in the area of the fracture gap appear around the lower anterior edge. The parallel plate construct had the highest stiffness among the three plating techniques in axial compression. In bending and varus loading the construct with the newly designed plate had the highest stiffness, but in axial compression demonstrated the lowest. The parallel plate configurations had higher stiffness than the perpendicular ones in all three loading directions and the difference is most pronounced in axial compression. CONCLUSION The displacements that appeared in all three plating systems are minimal and within the limits that meet the requirements of sufficient biomechanical stability in the usual time for the healing of fractures in that region. The newly designed Y-shaped plate for extra-articular fractures of the distal humerus is a possible alternative to the usual method of osteosynthesis with two plates in the case of an extra-articular fracture of the distal humerus. Further biomechanical studies are needed for a decisive conclusion.

Maxillary Fragment Stabilization After Le Fort I Fracture With 1 Screw Pair per Plate

PURPOSE The aim of the present study was to determine whether plates with only 1 screw pair can be used for Le Fort I fracture management. Good postoperative results motivated the direct application of mandible fixation principles to the fractured midface region without additional experimental research. However, the amount and distribution of the forces in the midface region is different from those on the mandible. MATERIALS AND METHODS Testing was conducted on plastic anatomic models. The validity of the experimental model was tested before the fixation techniques were compared. Standard miniplates and miniscrews were used for fixation of the maxilla. The model surface strain analysis was conducted using the noncontact object grating method, which enabled the surface strain measurement without direct influence on the measured model. RESULTS In 2 screw pair fixation, the outer screw pair has little effect on the local strain distribution, but it lowers the contact forces along the crack. One screw pair fixation is stable enough for fixation, but it has a greater strain peak at the crack edges. CONCLUSION Our results showed that 1 screw pair per plate was enough for stable fixation, and 2 or more screw pairs should only be used when the bone fragment at the fracture site cannot sufficiently transmit forces along the crack.

Experimental and Numerical Investigation of Fatigue Behaviour of Nodular Cast Iron

This paper presents an experimental and numerical study on two different types of the nodular cast iron EN-GJS-400-18-LT. The experimental procedure includes symmetrical and unsymmetrical strain controlled tests on the cylindrical specimens as well as crack initiation and propagation tests on the compact tension and single edged notched specimens. Different loading regimes are applied, and monitoring of the crack length during the tests is performed by an optical system. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is examined. Experimental results show that two material types have significantly different the crack behaviour.

Numerical and Experimental Analysis of a Frictionless Receding Contact between Cylindrical Indenter, Layer and Substrate

This paper investigates the behaviour of a receding contact when a cylindrical indenter presses an unbonded layer resting on a substrate. The problem is analysed by using FEM within the scope of the linear theory of elasticity and under the assumption of plane strain. This paper presents new and original results in the analysis of influence of load intensity and indenter geometry on the contact parameters. In addition, in the investigation into material properties a reference analysis was carried out for the case of material similarity between all three bodies, and material properties were subsequently varied for each body. This class of problems shows nonlinear behaviour, with both contact pressure distributions and contact half-widths found to depend nonlinearly on the applied load. The experimental analysis was carried out by employing the digital image correlation method and the ARAMIS 4M system was used. The obtained measurement results show good agreement with the numerical results.

A biomechanical comparison of four fixed-angle dorsal plates in a finite element model of dorsally-unstable radius fracture

PURPOSE To compare the finite element models of two different composite radius fracture patterns, reduced and stabilised with four different fixed-angle dorsal plates during axial, dorsal and volar loading conditions. METHODS Eight different plastic models representing four AO/ASIF type 23-A3 distal radius fractures and four AO/ASIF 23-C2 distal radius fractures were obtained and fixed each with 1 of 4 methods: a standard dorsal non-anatomical fixed angle T-plate (3.5mm Dorsal T-plate, Synthes), anatomical fixed-angle double plates (2.4mm LCP Dorsal Distal Radius, Synthes), anatomical fixed angle T-plate (2.4mm Acu-Loc Dorsal Plate, Acumed) or anatomical variable-angle dorsal T-plate (3.5mm, Dorsal Plate, Zrinski). Composite radius with plate and screws were scanned with a 3D optical scanner and later processed in Abaqus Software to generate the finite element model. All models were axially loaded at 3 points (centrally, volarly and dorsally) with 50 N forces to avoid the appearance of plastic deformations of the models. Total displacements at the end of the bone and the stresses in the bones and plates were determined and compared. RESULTS Maximal von Mises stress in bone for 3-part fracture models was very similar to that in 2-part fracture models. The biggest difference between models and the largest displacements were seen during volar loading. The stresses in all models were the highest above the fracture gap. The best performance in all parameters tested was with the Zrinski plate and the most modest results were with the Synthes T-plate. CONCLUSION There was no significant difference between 2-part (AO/ASIF type 23-A3) and 3-part (AO/ASIF 23-C2) fracture models. Maximal stresses in the plates appeared above the fracture gap; therefore, it is worth considering the development of plates without screw holes above the gap.

INFLUENCE OF GAP SHAPE ON BIOMECHANICAL PROPERTIES OF EXTRA-ARTICULAR DISTAL HUMERAL FRACTURE – A FINITE ELEMENT STUDY

The aim of the study was to assess the influence of gap shape on biomechanical results in extra-articular distal humeral fracture: with contact on the posterior part (by anterior gap) and contact on ulnar column (by radial gap). The goal was to examine if and to what extent did displacements decrease in comparison with previously examined parallel gap without bony contact. The finite element analysis on the three different plate constructs was performed, i.e. parallel, perpendicular and newly designed Y shape plate were considered. Displacements were measured on articular surface and gap point. The most visible decrease of maximum displacements in the distal part of the model was detected in the Y plate model with axial loading: in case of anterior gap 58.5% and especially at radially formed gap 60.9%. Similarly, at axial loading, displacement at the analyzed point on fracture gap most significantly decreased in Y plate model (by 49.4%) at posterior bony contact. Moreover, the latter showed displacement decrease by 68.5% at ulnar bone contact. Furthermore, if a longer radial plate than the ulnar one was used, varus stress could have been avoided. Study results suggested that sufficient stability could be ensured with the newly designed Y shape plate.

The Creep and Fracture Behaviour of the Polyethylene PE100

This paper presents an experimental and numerical study on the creep and fracture behaviour of the polyethylene PE100. The experimental procedure includes monotonic tests on the standard tensile specimen as well as creep-fracture tests on the axisymmetrically cracked specimens. Based on the experimental results, a new primary/secondary creep constitutive model is proposed to simulate the nonlinear and time dependent behaviour of considered material. The material parameters are computed from a leastsquare fit to experimental data obtained from tests at 80 °C. Within the framework of numerical investigations an algorithm for the integration of the constitutive law is derived. The derived algorithm in conjunction with the consistent tangent matrix is implemented in the finite element (FE) code ABAQUS by using the user subroutine CREEP. The accuracy of the proposed numerical algorithm is validated by comparing with experimental results.

STRENGTH AND RELIABILITY OF SHIPS 'AS-BUILT'

This report firstly presents the rule based scantlings and sectional properties of the example ship defined by using the nominal properties of mild shipbuilding steel. It also describes the way of collection of characteristic material specimens of rolled steel plates and bars delivered by the steel manufacturer to the shipyard for to the example ship. Secondly it summarizes the results of tensile testing in the Laboratory for experimental mechanics of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb of plates and bars denoted here as ‘in-built’ material properties for the example ship according to the production plans. The report then reminds on the rule based material properties for acceptance purposes. Next it considers the influence of ‘in-built’ mechanical properties with respect to the rule requirements on local, global and ultimate strength of ships. The report discusses material properties other than yield strength, which participate in the assessment of the overall ship safety such as the weld strength, buckling and fatigue strength, low temperature behavior, corrosion and reliability. The results of the tensile testing of ‘in-built’ materials are then applied to checking of the local, global and ultimate ‘asbuilt’ strength of the example ship’s hull instead of the ‘asdesigned’ strength defined by the nominal material properties. The report at the end discusses the differences between the ‘as-designed’ and the ‘as-built’ hull strength, fatigue life and reliability. It suggests minimization of the hull strength uncertainties by adopting the mechanical properties of ‘inbuilt’ materials. The conclusion supports the stirring idea of this report that in addition to the ‘as-designed’ strength, a ship deserves individualized assessment of the “as-built” ship hull strength based on the measured realistic ‘in-built’ properties.

Modelling of cyclic plasticity and crack propagation

An experimental and numerical study of the cyclic deformation and low-cycle fatigue behaviour of the aluminium alloy AlCu5BiPb–T8 is presented. The experimental program included monotonic tensile tests, symmetric and unsymmetric strain-controlled fatigue tests, fracture toughness tests, as well as fatigue crack initiation and propagation tests. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is proposed. This algorithm is implemented into the finite element program ABAQUS and applied to the analysis of a crack growth near the notch. The accuracy of the computational procedure is tested by comparing the computed results with the real experimental data.