Nondestructive acoustic modal analysis for assessing bone screw stability: An ex vivo animal study

Conventional insertion torque and pull-out tests are destructive and unsuitable for clinical bone screw fixation. This study evaluates screw stability using acoustic modal analysis (AMA) and Periotest compared to traditional methods in an ex vivo animal model. Titanium self-tapping screws (STS) and nonself-tapping screws (N-STS) were implanted in the proximal tibia of 12 rabbits. Four testing methods were used to assess screw stability: peak insertion torque (PIT) during implantation, AMA for natural frequency (NF), Periotest for Periotest value (PTV), and pull-out test for peak pullout force (PPF). Euthanization was performed at 0 (primary stability), 4, and 8 weeks (secondary stability). No significant difference in primary stability was found between STS and N-STS except for AMA (STS: NF 2434 ± 67 Hz, N-STS: NF 2572 ± 43 Hz; p = 0.62). Secondary stability increased significantly over time for both screw types (4-week: NF 3687 ± 36 vs. 3408 ± 45 Hz, PTV 1.4 ± 1.6 vs. -1.5 ± 1.8, PPF 236 ± 29 vs. 220 ± 34 N; 8-week: NF 3890 ± 39 vs. 3613 ± 31 Hz, PTV -3.2 ± 2.5 vs. -2 ± 4.3, PPF 248 ± 25 vs. 289 ± 28 N). Higher NF values for given PTV/PPF indicate potential clinical advantages. Significant differences between primary and secondary stabilities suggest osteointegration was mainly achieved in the 4-week group.

DESIGN AND NUMERICAL ANALYSIS OF FACE MASK POLYMER SHIELD AGAINST INFECTIOUS DISEASES

Viruses that cause infections spread very quickly and has a fatal risk to people with chronic diseases. Since the virus vaccine and the drugs to be used in treatment are not fully developed, alternative ways to protect from the virus are being investigated. The Covid-19 virus has been recognized by the World Health Organization (WHO) as a pandemic. In this study, the effect of face mask shield against Covid-19 and other infections were investigated using finite element analysis (FEA). Three-dimensional model of the conventional face mask, equipment and shield was performed with the SolidWorks software. Computer-aided simulations were performed using AnsysWorkbench explicit dynamics module. The loading, boundary conditions and material properties were defined in the AnsysWorkbench. The effects of droplets formed because of cough or sneezing on the human model with mask and shield were analyzed. It has been confirmed from the analyzes that both the mask and the shield are effective against the virus.

A comparative study of tapped and untapped pilot holes for bicortical orthopedic screws – 3D finite element analysis with an experimental test

The aim of this study was to compare the screw-to-bone fixation strength of two insertion techniques: self-tapping screw (STS) and non-self-tapping screw (NSTS). Finite element analysis (FEA) was used for the comparison by featuring three tests (insertion, pull-out and shear) in a human tibia bone model. A non-linear material behavior with ductile damage properties was chosen for the modeling. To validate the numerical models, experimental insertion and pull-out tests were carried out using a synthetic bone. The experimental and numerical results of pull-out tests correlated well. Thread forming was successfully simulated during the insertion process of STS and NSTS. It is demonstrated that the STS generates higher insertion torque, induces a higher amount of stress after the insertion process and relatively more strength under the pull-out and shear tests than the NSTS. However, the NSTS induces more stiffness under the two tests (pull-out and shear) and less damage to the screw-bone interface compared to the STS. It is concluded that the use of STS ensures tighter bony contact and enables higher pull-out strength; however, the use of NSTS improves the stiffness of the fixation and induces less damage to the cortical bone-screw fixation and thus minimum risk is obtained in terms of bone necrosis.

Comparison of Biomechanical Effects of Different Configurations of Kirschner Wires on the Epiphyseal Plate and Stability in a Salter-Harris Type 2 Distal Femoral Fracture Model

BACKGROUND

We sought to investigate the different configurations of Kirschner wires used in distal femur Salter-Harris (SH) type 2 epiphyseal fracture for stabilization after reduction under axial, rotational, and bending forces and to define the biomechanical effects on the epiphyseal plate and the fracture line and decide which was more advantageous.

METHODS

The SH type 2 fracture was modeled using design software for four different configurations: cross, cross-parallel, parallel medial, and parallel lateral with two Kirschner wires, and computer-aided numerical analyses of the different configurations after reduction were performed using the finite element method. For each configuration, the mesh process, loading condition (axial, bending, and rotational), boundary conditions, and material models were applied in finite element software, and growth cartilage and von Mises stress values occurring around the Kirschner wire groove were calculated.

RESULTS

In growth cartilage, the stresses were highest in the parallel lateral configuration and lowest in the cross configuration. In Kirschner wires, the stresses were highest in the cross configuration and lowest in the cross-parallel and parallel lateral configurations. In the groove between the growth cartilage and the Kirschner wire interface, the stresses were highest in the parallel lateral configuration and lowest in the cross configuration.

CONCLUSIONS

The results showed that the cross configuration is advantageous in fixation. In addition, in the SH type 2 epiphyseal fracture, we believe that the fixation shape should not be applied in the lateral configuration.

Obtaining patient-specific point model of the human ilium bone in the case of incomplete volumetric data using the method of parametric regions

In this paper, we present the methodology for determining the point model of the ilium bone in cases when volumetric data of the whole bone are not available. An extreme traumatic bone damage, osteoporosis, destruction of bone tissue by malignant bone tumors or the existence of only 2D medical image (X-ray) can be the reason for the lack of complete volumetric data. Points on the bone surface were defined at the curves that run through 26 previously defined parameters, at the edges of anteroposterior (A-P) and lateral projections and at the parts of the surface between some parameters. Those parts of the surface, enclosed by parameters, represent ten parametric regions. The values of coordinates, which represent the input data in the statistical program, were measured in a uniquely defined coordinate system. After establishing the correlations between the values of coordinates, 8869 different linear and nonlinear regression models were obtained. The prediction values for point coordinates were calculated and exported to a CAD program. Results obtained were tested on a randomly chosen male right ilium bone, applying the methodology for creating the prediction model using the method of parametric regions, which allows creating a complete polygonal model, for each region separately or just for some parts of the region. Results obtained in the form of regression equations for the right ilium bone can be applied to the left ilium bone. The results of the research were verified using a comparative deviation and distance analysis between the initial and obtained polygonal models.