finite element method

This article presents a mathematical justification for a new approach to arthroscopic stitching of the knee joint meniscus, based on a 3D computer model of the meniscus developed using the COMPASS-3D (APMFEM) program and AutodeskInventorPRO. The research with the patent RK No. 35413 dated 10.12.2021, titled "Method of arthroscopic stitching of the meniscus of the knee joint" builds upon the work of Yu.V. Labunsky.

Mathematical analysis was performed to compare two methods of stitching the meniscus: the new oblique-vertical stitch and the classical vertical stitch. The contact area of the meniscus tissues in the area of the rupture was measured for both stitching methods.

The findings demonstrate that the new oblique-vertical stitch offers a 1.5 times larger contact area of the meniscus tissues in the area of the rupture, compared to the classical vertical stitch. Additionally, the new method provides a more significant grip on the radial and circular fibers of the meniscus, surpassing the capabilities of the classic seam.

The results of this study can be utilized to develop practical recommendations for traumatologists regarding arthroscopic stitching of the meniscus in the knee joint. The new approach, supported by mathematical analysis and a 3D computer model, offers improved outcomes in terms of contact area and grip on the meniscus fibers, potentially leading to enhanced surgical techniques and patient outcomes.

The Boundary Element (BE) and Finite Element (FE) methods are widely used numerical techniques to solve the Electroencephalography (EEG) forward problem. However, the FE Method (FEM) has difficulty in simulating current dipoles due to singularity, and the BE method (BEM) cannot simulate inhomogeneous and anisotropic conductivity profiles. Recently, a hybrid BE-FE method has been proposed to benefit from the advantages of both BEM and FEM in solving the EEG forward problem. Generally, the type of mesh may significantly influence the results of numerical EEG forward solvers and should be carefully studied.

In this paper, the performance of the hybrid BE-FE method is compared with an approach of FEM (partial integration) using three types of meshes. The ground truth is the analytical EEG forward solutions obtained from inhomogeneous and isotropic/anisotropic four-layer spherical head models with dipoles of radial and tangential directions at four eccentricities.

The minimum mean of Relative Difference Measure (RDM) obtained from Partial Integration (PI)-FEM is 0.0596 at 70% source eccentricity while by using the hybrid BE-FE method it is improved to 0.0251 at the same eccentricity. On the other hand, the maximum mean of Magnitude Ratio (MAG) obtained from PI-FEM is 0.6216 at 50% source eccentricity while it is improved to 0.9734 at the same eccentricity.

The results show that the hybrid BE-FE method outperforms PI-FEM in solving the EEG forward problem using three types of meshes regarding RDM and MAG error criteria.

The present study aimed to assess the stress and strain distribution on mini-screws and the surrounding bone in cases of different cortical bone thicknesses (CBTs), mini-screw insertion angles, and force directions using finite element analysis (FEA).

Inventor professional version 8 software was used to construct 24 three-dimensional assemblies of mini-screws inserted with different insertion angles (30º, 60º, and 90º) in alveolar bone blocks with different CBTs (0.5, 1, 1.5, and 2 mm). The models simulated mini-screws inserted in bones with different CBTs and different insertion angles. A 2-N load was applied in two directions to mini-screw heads. The resultant stresses of the applied load were collected from the output of the ANSYS program.

The results indicated that force direction affected bone strains as the horizontal force generated more strains on cortical bone than the oblique one. Force applied to 60º inserted mini-screws generated much more strains on cortical bone than 90º and 30º inserted miniscrews. In a 60º inserted mini-screw, the horizontal force generated about 45% more strains on cortical bone than the oblique one. The exerted microstrain on bone decreased as CBT increased.

It can be concluded that inserting mini-screws at 60º to the bone surface should be avoided as it generates much more strains on cortical bone than 90º and 30º, especially when a force parallel to the bone surface is applied.

The finite element method (FEM) is an engineering tool to assess the mechanical behavior of a structure under applied loads. This method was first applied for stress analysis of mechanical structures in the late 1950s. Later on, this new method got the application in biomedical engineering by analyzing the mechanical behavior of human femora. With the advent of faster computers, more advanced imaging modalities, and better FE software resulting in increased sophistication in 3D modeling, FE models have been greatly improved and the possibility of creating a FE model that can closely mimic the geometry and material properties of bones of an individual patient, so-called a patient-specific model, is accessible. The objective of this editorial is to try to elucidate the advancements in and applications of patient-specific finite element modeling and discuss whether such models can give promising results in predicting the outcome of orthopedic surgeries and enter clinical practice as a decision support system.

Partial fibulectomy has been suggested for patients who encounter with severe varus/valgus or ununited fractures of the tibia. This study develops a finite element (FE) model of partial fibulectomy to study stress distribution in the tibiofemoral joint.

A 3D magnetic resonance imaging (MRI)-based of tibiofemoral joint and FE model was developed for study from a man volunteer with the normal left knee. Components consisted of the exact geometry of femur, tibia, fibula, meniscus, and articular cartilages. Firstly, geometries were constructed in Mimics and then exported to Rapid Forming XOR2 and finally, the Computer-aided design (CAD) model was analyzed in ABAQUS 6.10. Mechanical properties of the model for soft tissues were considered to be linear elastic, isotropic and homogenous and for bony parts were considered to be rigid.

Model predictions were compared with normal one and used to derive stress distribution under physiological loading for standing in quasi- static condition. The results showed load transferring toward lateral condyle due to partial fibulectomy. The variation of stress distribution would increase the risk of osteoarthritis.

Our results have been predicted that partial fibulectomy could be an unknown risk factor for osteoarthritis and the model could be used for extended similar studies.

The most common problem associated with dental implants is the abutment screw loosening. This research aimed to investigate the effect of the type of connection on screw loosening, using a finite element method (FEM).

Periosave system and different types of the implant–abutment connection were used for modeling. After being measured, CAD files were modeled using CATIA software and imported to the ANSYS analysis software, and the model was loaded.

A force of 100 N was applied at 0.1 second, and no force was applied at 0.42 second. The screw head deformation at 0.1 and 0.42 seconds was 8 and 3.8 μm, and 7.6 and 2.8 μm at morse taper and octagon dental implant connections, respectively. The displacement rate of the internal surface of the abutment at 0.1 and 0.42 seconds was 10.7 and 8.4 μm, and 5.7 and 5.6 µm in the octagon and morse taper dental implant connections, respectively. The displacement of the implant suprastructure–abutment interface from the screw head at 0.1 and 0.42 seconds was 9 and 7 μm, and 7 and 6 μm in the morse taper and octagon dental implant connections, respectively. At intervals of 0 to 0.1 seconds and 0.6 to 0.8 seconds, the octagon connection was separated at the maximum screw head displacement and the internal part of the abutment, but the morse taper connection did not exhibit any separation. In the above time intervals, the results were similar to the maximum state in case of the minimum displacement of the screw head and the internal part of the abutment.

Screw loosening is less likely to occur in the morse hex connection compared to the octagon connection due to the lack of separation of the screw from the internal surface of the abutment.

Multifunctional nanomedicine is the new generation of medicine, which is remarkably promising and associated with the minimum toxicity of targeted therapy. Distribution and transport of nanoparticles (NPs) in the blood flow are essential to the evaluation of delivery efficacy.

In the present study, we initially designed a phantom based on Murray’s minimum work law using the AutoCAD software. Afterwards, the phantom was fabricated using lithography and imaged using a Siemens Magnetom 3T Prisma MRI scanner at the National Brain Mapping Laboratory, Iran. Finally, the velocity and pressure in the capillary network were simulated using the COMSOL software. Moreover, three-dimensional Navier-Stokes equations were applied to model the NP transport and dispersion in blood suspension.

According to the findings, particle size, vessel geometry, and vascular flow rate affected the delivery efficacy and NP distribution. Cerebral blood flow, cerebral blood volume, mean transit time, and curves for the capillary network were obtained at different times. The simulations indicated that the velocity and pressure in the capillary network were within the ranges of 0.0001-0.0005 m/s and 5-25 mm/Hg, respectively. Higher particle concentration was also observed in the non-uniform NP distribution profile near the vessel wall.

We investigated the effects of the vessel size and geometry and particulate nature of blood on the delivery and distribution of NPs. For targeted drug delivery applications, a mechanistic understanding on the nanomedicine design was provided as well.

Joint replacement surgery in the wrist is less common than other replacement, but can be an option if you have painful arthritis that does not respond to other treatments.
In wrist joint replacement surgery, the damaged parts of the wrist bones are removed and replaced with artificial components, called a wrist prosthesis. If the cartilage is worn away or damaged by injury, infection, or disease, the bones themselves will rub against each other, wearing out the ends of the bones. This causes a painful, arthritic condition. Osteoarthritis, the most common form of arthritis, results from a gradual wearing away of the cartilage covering on bones. Rheumatoid arthritis is a chronic inflammatory disease of the joints that results in pain, stiffness and swelling. Rheumatoid arthritis usually affects several joints on both the right and left sides of the body. Both forms of arthritis may affect the strength of the fingers and hand, making it difficult to grip or pinch.

Giant cell tumor (GCT) is a primary and benign tumor of bone, albeit locally aggressive in some cases, such as in the epi-metaphyseal region of long bones, predominantly the distal end of femur and proximal end of tibia (1). There are a variety of treatments for a bone affected by GCT, ranging from chemotherapy, radiotherapy, embolization, and cryosurgery, to surgery with the use of chemical or thermal adjuvant (2). Even with advances in new chemotropic drugs, surgery is still the most effective treatment for this kind of tumor (3). The surgery often involves defect reconstruction following tumor removal (4). The aims of treatment are removing the tumor and reconstructing the bone defect in order to decrease the risk of recurrence, and restore limb function, respectively. To achieve these goals, reconstruction is usually accompanied with PMMA bone cement infilling (4). The high heat generated during PMMA polymerization in the body can kill the remaining cancer cells, and hence the chance of recurrence decreases (5). In addition, filling the cavity with bone cement provides immediate stability, enabling patients to return to their daily activities soon (6).
The major drawbacks of the technique of curettage and cementation is the high fracture risk, due to the early loading of the bone, and the insufficient fixation of the cement in the cavity (7). Hence, several methods have been developed to fix the bone cement in order to prevent the postoperative fracture. Pattijn et.al packed the cement with a titanium membrane which was attached to the periosteum with small screws (7). The membrane can make early normal functioning of patients possible, since it partially restore the strength and stiffness of the bone. Cement augmentation with internal fixation is another method to decrease the risk of postoperative fractures (6, 8, 9).