MPa In Model Research Articles

Impact of transpedicular fixation on thoracolumbar junction burst fracture stability: a biomechanical perspective

Introduction. The treatment of burst fractures at the thoracolumbar junction remains a contentious issue in vertebrology. Despite a broad array of surgical interventions available, many surgeons favor isolated posterior stabilization, which can be performed using either minimally invasive or open approaches. However, the biomechanical properties of these methods have not been thoroughly investigated. Objective: This study aims to evaluate the biomechanical stability of the thoracolumbar junction following transpedicular stabilization of a burst fracture at the Th12 vertebra, under different system configurations influenced by lateral flexion. Materials and Methods: A mathematical finite element model of the human thoracolumbar spine, featuring a burst fracture at the Th12 vertebra, was developed. The model included a transpedicular stabilization system with eight screws, simulating “long” stabilization. We examined four variants of transpedicular fixation using both mono- and bicortical screws, with and without the inclusion of two cross-links. Results: The study found that the load borne by the damaged Th12 vertebral body varied depending on the fixation system employed. Specifically, stress levels were 24.0 MPa, 27.3 MPa, 18.4 MPa, and 25.8 MPa for models with short screws without cross-links, long screws without cross-links, short screws with cross-links, and long screws with cross-links, respectively. At the screw entry points in the vertebral arch, the highest stress values were recorded at the L2 vertebra, showing 11.8 MPa, 14.0 MPa, 9.4 MPa, and 13.4 MPa for each respective model. Among the metal construct elements, the connecting rods consistently exhibited the highest stress, with values of 226.7 MPa, 313.4 MPa, 212.4 MPa, and 293.98 MPa, respectively. Conclusion: The results underscore that utilizing cross-links in the stabilization of burst fractures at the thoracolumbar junction, which is only feasible through an open installation, somewhat mitigates stress within the stabilized spinal segment. Meanwhile, the modeling of lateral flexion revealed only minimal differences in stress values between open and minimally invasive installations.

Enhanced orthopedic implant design for transfemoral amputation incorporating a honeycomb structure technology

After lower limb amputation, the primary challenge is to facilitate the patient’s adoption of a prosthetic limb seamlessly, without encountering complications or discomfort. Elevated stress levels within the residual limb, experienced when wearing the socket and while standing or walking, contribute to patient discomfort. As an initial step in this study, we developed a finite element model of above-knee amputation. Additionally, we designed a prototype orthopedic implant composed of several parts, with the lower section featuring a honeycomb structure aimed at absorbing and diminishing stresses at the interface of the residual limb and prosthetic. In this study, finite element models with and without orthopedic implants were analyzed to assess the feasibility and impact of incorporating a honeycomb structure within the implants on stress distribution, particularly at the stump-prosthetic interface. Models with honeycomb-structured implants, at varying densities, showed a reduction in interface stress to approximately 2.15e-2 MPa and 2.01e-2 MPa, compared to 4.5e-2 MPa in model without honeycomb structure in the implant and 7.97e-2 MPa in models without any implants.

Different internal fixation methods for Hoffa-like fractures of the tibial plateau: a finite element analysis.

Due to the low incidence of posteromedial tibial plateau fractures and limited clinical data available, the optimal treatment for this type of fracture remains to be established. This type of fracture, also known as Hoffa-like fracture of the tibial plateau, shares a similar mechanism of injury with the Hoffa fracture of the femoral condyle. In the field of orthopedics, finite element analysis is considered a valuable method to guide clinical decision-making. In this study, four methods used for internal fixation of Hoffa-like fractures of the tibial plateau were compared using computer simulation and applying a finite element method (FEM). The methods compared were lateral L-plate fixation alone (Model A); lateral L-plate combined with posterior anti-slip plate (reconstruction plate/T-plate) fixation (Model B); lateral L-plate combined with posterior hollow nail fixation of the fracture block (Model C); and lateral L-plate combined with anterior hollow nail fixation of the fracture (Model D). The maximum displacement of the model and the maximum stress of the internal fixation material were analyzed by applying an axial load of 2,500 N. The results showed that, in the normal bone model, the maximum displacement of the fracture in Model A was 0.60032 mm, with improved stability through the addition of posterior lateral plate fixation in Model B and reduction of the displacement to 0.38882 mm. The maximum displacement in Model C and Model D was comparable, amounting to 0.42345 mm and 0.42273 mm, respectively. Maximum stress was 1235.6 MPa for Model A, 84.724 MPa for Model B, 99.805 MPa for Model C, and 103.19 MPa for Model D. In the internal fixation analysis of the osteoporotic fracture model, we observed patterns similar to the results of the normal bone model. The results indicated that Model B yielded the overall best results in the treatment of Hoffa-like fractures of the tibial plateau. The orthopedic surgeon may wish to implement these insights into the perioperative algorithm, thereby refining and optimizing clinical patient care. In addition, our findings pave the way for future research efforts.

Sloped marginal configuration design of implants as an alternative innovation to the grafting operations: a three-dimensional finite element analysis

Aim: Dental implant operations often require bone grafting due to bone resorption in the buccal area, which make the treatment more complicated, increase the risk of complications, and results in extra costs and prolongation of treatment. This study aimed to evaluate the biomechanical behavior of the implants with a sloped marginal configuration design in the alveolar ridge with a level difference between the buccal and lingual bone levels using three-dimensional finite element analysis (FEA) method. 
 Material and Method: Two implant models with different marginal configuration designs were used in this study. Implants were placed in the posterior edentulous mandible models in which the buccal region had a 2 mm more resorption according to lingual region which were created by imitating natural bone resorption with FEA. Bone grafting was performed on the exposed buccal surface in the conventional flat marginal configuration implant model (Model 1). In contrast, the sloped marginal configuration implants were compatible with the difference in bone level and placed directly without any additional surgical procedures (Model 2). Than three unit fixed partial dentures were designed. The design of cortical and cancellous bones, prosthetic components, implants, abutment screws and abutments covering those in the edentulous mandible models were transferred to digital three-dimensional models that were created to mimicking the real structures. The models were fixed below and behind of the mandible with zero movement. Load transfer characteristics of both models under these essential limitations were evaluated under 200N foodstuff force.
 Results: The highest von Mises stress value was observed as 69.300 MPa in Model 1 and 126.870 MPa in Model 2. The maximum principal stress values were 28.236 N/mm2 and 63.449 N/mm2; the minimum principal stress values were 38.346 N/mm2 and 43.643 N/mm2 in Model 1 and Model 2, respectively. The highest von Mises stress value, maximum principal stress and minimum principal stress values were found higher in Model 2 which was created with sloped marginal configuration design of implants but all values were observed within acceptable physiological limits.
 Conclusion: The sloped marginal configuration design of implants can be a non-invasive and more economical treatment alternative modality compared to conventional flat marginal configuration implants with advanced surgeries during implant placement.

Can a coracoclavicular screw added to the clavicular hook plate reduce subacromial stress? A finite element analysis.

The aim of this study was to investigate the stresses on the plate and the clavicle in the standard clavicular hook plate model and the clavicular hook plate models with a coracoclavicular (CC) screw by finite element analysis (FEA). The FEA models were created with the combination of acromion, clavicle, coracoid process, 8-hole clavicular hook plate and screw components. Model 1 was created as a standard clavicular hook plate model and plates were implanted to the clavicle and the acromion by six locking screws. Model 2 was created by a cortical screw placed in the coracoid process through the third hole of the plate (CC screw) and fixation of hook plate by five locking screws. The upward-pull force was applied to clavicle at the insertion of sternocleidomastoid muscle with three axes. The stress exerted by acromion on the hook of the plate, stresses on the plate, clavicle, and CC screw were analyzed. When the screw holes were compared, in Model 1, the highest stress was found in the last hole of the plate. In Model 2, the highest stress was detected on the CC screw. The stress on the clavicle was found to be 0.14 Mpa in Model 1 and 0.21 Mpa in Model 2. In Model 1 and Model 2, the stress exerted by acromion on the subacromial part of the plate was found to be 2.05 KPa and 1.66x10-6 KPa, respectively. The results of this study show that addition of CC screw to the standard clavicular hook plate shares the loading and reduces the stress on the hook of the plate.

Finite element modeling of maximum stress in pelvic floor structures during the head expulsion (FINESSE) study.

Several studies have assessed birth-related deformations of the levator ani muscle (LAM) and perineum on models that depicted these elements in isolation. The main aim of this study was to develop a complex female pelvic floor computational model using the finite element method to evaluate points and timing of maximum stress at the LAM and perineum in relation to the birth process. A three-dimensional computational model of the female pelvic floor was created and used to simulate vaginal birth based on data from previously described real-life MRI scans. We developed three models: model A (LAM without perineum); model B (perineum without LAM); model C (a combined model with both structures). The maximum stress in the LAM was achieved when the vertex was 9 cm below the ischial spines and measured 37.3MPa in model A and 88.7MPa in model C. The maximum stress in the perineum occurred at the time of distension by the suboocipito-frontal diameter and reached 86.7MPa and 119.6MPa in models B and C, respectively, while the stress in the posterior fourchette caused by the suboccipito-bregmatic diameter measured 36.9MPa for model B and 39.8MPa for model C. Including perineal structures in a computational birth model simulation affects the level of stress at the LAM. The maximum stress at the LAM and perineum seems to occur when the head is lower than previously anticipated.

Analysis of stress distribution in lingual orthodontics system for effective en-masse retraction using various combinations of lever arm and mini-implants: A finite element method study

The aims and objectives of this study were to evaluate the von Mises stress and principal stress distribution and displacement of anterior teeth in a lingual orthodontics system along the periodontal ligament and alveolar bone by various combinations of mini-implants and lever arm during en-masse retraction. Four 3-dimensional finite element (FE) models of the bilateral maxillary first premolar extraction cases were constructed. Lingual brackets were (0.018-in slots) positioned over the center of the clinical crown. In all 4 models, 150g of retraction force was applied with the help of a nickel-titanium closed coil spring with different combinations of mini-implants and lever arm on each side. FE analysis was then performed to evaluate stress distribution, principal stress, von Mises stress, and displacement of the anterior teeth using ANSYS software (version 12.1; Ansys, Canonsburg, Pa). The FE study was enough to validate the analysis results obtained by software tools with FE simulation instead of experimental readings. Thus, statistical analysis was not required. In this study, maximum tensile stresses were observed in the periodontal ligament at the mesial cervical region of the canine with values of 1.84MPa, 2.02MPa, 1.88MPa, and 2.08MPa for models 1-4, respectively. Maximum von Mises stress in alveolar bone was 8.05MPa, 8.23MPa, 8.19MPa, and 8.37MPa for models 1-4, respectively, which was within the optimum limit (135MPa). Variable amounts of displacements like lingual crown tipping, lingual root tipping, and extrusion were observed in all the models. The 15-mm long lever arm models (models 2 and 4) showed a more controlled crown (0.015mm) and root movement (0.004mm) compared with 12-mm long lever arm models (models 1 and 3). In lingual orthodontics, controlled root movement increased as we increased the length of the lever arm. It was also concluded that the amount of increased controlled tipping found with the placement of the mini-implant was toward the palatal slope.

Glenoid bone resorption after Bankart repair: finite element analysis of postoperative stress distribution of the glenoid

There are various modifications of the Bankart repair, and postoperative changes to the glenoid morphologyafter the repair are reported. Among the various procedures performed, a decrease in the lateral glenoid diameter might be related to the surgery that involves removal of the articular cartilage and repair of the labrum-anterior inferior glenohumeral ligamentcomplex on the glenoid surface. This is in contrast to cases without significant bony Bankart lesionsthat are not on the edge of the glenoid. Thus, this study aimed to compare glenoid rim stress after Bankart repair using 2 methods of finite element analysis: a method of removing the anteroinferior cartilage and repairing the glenohumeral ligament complex on the glenoidand a method of preserving the cartilage and repairing the glenohumeral ligament complex on the glenoid edge. Five preoperative computed tomography scans of patients with traumatic anterior instability who underwent arthroscopic Bankart repair were used. Two models simulating different surgical procedures were created as follows: in model G, a 5-mm-thick cartilage on the glenoid rim was removed between 2 and 7 o'clock, and the glenohumeral ligament complex was repaired on the medial edge of the glenoid bone where the cartilage was removed. In model E, the cartilage on the glenoid rim was not removed, and the glenohumeral ligament complex was repaired on the glenoid edge. The load stresses on the anteroinferior area of the glenoid after Bankart repair with models G and E were measured using finite element analysis. The stress on the glenoid at 3-4 o'clock was 3.16 MPa in model G and 6.42 MPa in model E (P = .043). The stress at 4-5 o'clock was 1.68 MPa in model G and 4.53 MPa in model E (P = .043). The stress at 5-6 o'clock was 2.26 MPa in model G and 3.93 MPa in model E (P = .043). Significantly lower load stresses were observed at the anteroinferior rim of the glenoid in model G than in model E.

Risk of rod fracture according to cross-link position in pedicle subtraction osteotomy (PSO): A finite element study

PurposeThe purpose of this study is to investigate the effect of the cross-link position on the rod fracture phenomenon during pedicle subtraction osteotomy (PSO) surgery using finite element model (FEM). MethodsA three-dimensional finite element model of a lumbar spine with sagittal imbalance was constructed using computed tomography data of a 65-year-old female patient. After simulating the standard PSO at the L4 level, we constructed four models, specifically a model without a cross-link and three models with a cross-link at three different sites. The peak von Mises stress (PVMS) of the rod around the PSO site was measured after applying physiological loads (flexion, extension, axial rotation, and lateral bending) in each model. ResultsThe measured PVMS outcomes at the PSO site were 135.8, 135.9, 208.9, and 384.7 MPa for model 1, 2, 3, and 4 during flexion, and 180.0, 180.1, 210.1, and 445.7 MPa during extension. These results show that when the cross-link is located at the PSO site, the rod stress at the PSO site increases significantly during flexion and extension. As the cross-link moved away from the PSO site, the effect on the rod stress decreased. When the cross-link was placed two levels away from the PSO site, the rod stress was scarcely affected. ConclusionWhen the cross-link during PSO surgery was positioned two levels away from the PSO site, the risk of rod fracture did not increase.

The combined impact of mechanical factors on the wall stress of the human ascending aorta \u2013 a finite elements study

Biomechanical factors influence stress in the aortic wall. The aim of this study was to assess how the diameter and shape of the vessel, blood pressure and longitudinal systolic aortic stretching (SAS) caused by the contraction of the myocardium influence stress in the aortic wall. Three computational models of the non-dilated aorta and aneurysms of the ascending aorta and aortic root were created. Then, finite elements analyses were carried out. The models were subjected to blood pressure (120 mmHg and 160 mmHg) and longitudinal systolic aortic stretching (0 mm, 5 mm, 10 mm and 15 mm). The influence of wall elasticity was examined too. Blood pressure had a smaller impact on the stress than the SAS. An increase in blood pressure from120 mmHg to 160 mmHg increased the peak wall stress (PWS) on average by 0.1 MPa in all models. A 5 mm SAS caused a 0.1–0. 2 MPa increase in PWS in all the models. The increase in PWS caused by a 10mm and 15mmSAS was 0.2 MPa and 0. 4 MPa in the non-dilated aorta, 0.2–0.3 MPa and 0.3–0.5 MPa in the aneurysm of the ascending aorta, and 0.1–0.2 MPa and 0.2–0.3 MPa in the aortic root aneurysm model, respectively. The loss of elasticity of the aneurysmal wall resulted in an increase of PWS by 0.1–0.2 MPa. Aortic geometry, wall stiffness, blood pressure and SAS have an impact on PWS. However, SAS had the biggest impact on wall stress. The results of this study may be useful in future patient-specific computational models used to assess the risk of aortic complications.

Hip joint geometry effects on cartilage contact stresses during a gait cycle.

The cartilage surface geometry of natural human hip joint is commonly regarded as sphere. It has been widely applied in computational simulation and hip joint prosthesis design. Some new geometry models have been developed and the sphere assumption has been questioned recently. The objective of this study was to analyze joint geometry effects on cartilage contact stress distribution and investigate contact patterns during a whole gait cycle. Hip surface was reconstructed from CT data of a healthy volunteer. Three finite element (FE) models of hip joint were developed from different cartilage geometries: natural geometry, sphere and rotational ellipsoid. Loads at ten instants of gait cycle were applied to these models based on published in-vivo data. FE predictions of peak contact pressure during gait of natural hip were compared with sphere and rotational ellipsoid replaced hip joint. Contact occurs mainly in upper anterior region of both acetabulum and femur distributing along sagittal plane of human body. It moves towards inferolateral aspect as the resultant joint reaction force changes during walking for natural hip. Peak pressures at the instant with maximum contact force were 7.48 MPa, 14.97 MPa and 13.12 MPa for models with natural hip surface, sphere replaced and rotational ellipsoid replaced surface respectively. During the whole gait cycle, contact pressure of natural hip ranked lowest in most of the instants, followed by rotational ellipsoid replaced and sphere replaced hip. The results indicate that rotational ellipsoid is more consistent with natural hip cartilage geometry than sphere during normal walking. This means rotational ellipsoid prosthesis could give a better description of physiological structure compared with standard sphere prosthesis. Therefore, rotational ellipsoid would be a better choice for prosthesis design.

Finite element stress analysis study for stresses around mandibular implant retained overdenture MIR-OD

Background: It has been well known that the success of mandibular implant- retained overdenture heavily depends on initial stability, retention and long term osseointegration this is might be due to optimal stresses distribution in surrounding bones. Types of mandibular implant- retained overdenture anchorage system and number of dental implants play an important role in stresses distribution at the implant-bone interface. It is necessary to keep the stresses below the physiologic tolerance level of the bone .since. And it is difficult to measure these stresses around bone in vivo. In the present study, finite element analysis used to study the stresses distribution around dental implant supporting Mandible implant retained overdenture Materials and methods: Eight models were constructed including four designs of anchorage system (ball-cup, ball-O Ring, bar without distal extension and bar with distal extension).The first group of models were supported by four dental implant and second group of models were supported by two dental implant only. Models constructed from the data obtained directly from patient The contour of bone was obtained from C.T scan image of patient, then data transferred to ANSYS program for modeling then load applied and solve the equation by the program, Specified nodes were selected at the rings of crestal bone (cortical bone) and cortical cancellous interface around each dental implant and fixed for all models to monitor the stress change in that regions of different design of MIR-OD.. After load application, Specified nodes were selected at the rings of crestal bone (cortical bone) and cortical cancellous interface around each dental implant and fixed for all models to monitor the stress change in that regions of different design of MIR-OD . Results: In the present study the stress distribution and maximum stresses value around dental implant had a relationship to the number of dental implant. , The result appeared that the maximum stresses and means of stresses value was lower in the first group of models (which was supported through the use four dental implant) than the second group of models (which was supported through the use of two dental implant only). For the first group of models the maximum stresses value around mesial implant was11.67, 10.51, 10.98 and 10.72 Mpa, while the maximum stresses around distal implant was 21.33, 18.51, 18.86, and17.56 Mpa for models 1,2,3 and 4respectively ,and the stresses around implant supporting second group of models was 22.52, 22.16, 20.51 and 19.60 Mpa for models 5,6,7and8 respectively .Statistical analyses of means value appeared that there was statistically significant difference in stresses means value around implant of the second group with that’s values around mesial and distal implant supporting first group of model . Regarding the result of both ball and bar system, it has been demonstrated that stress was greater with ball attachment and MIR-OD supported by the use of four dental implants and anchored by bar attachments with distal extension gives the minimum values of stresses than the rest models. Also the results show that higher stresses value was appeared at the cortical bone ring surrounding dental implant especially the distal implant nearest to the free end extension area. Also it was appeared that the best model was Mandible implant- retained overdenture that’s anchored by bar with distal extension and support by four dental implant. Conclusions: Bar-clips with distal extension mode of attachment considered the best type in producing the least stresses around dental implant regardless number of dental implant used.

IPS-Empress II inlay-retained fixed partial denture reinforced with zirconia bar: Three-dimensional finite element and in-vitro studies

Objective. This study evaluated von Mises stress distribution, flexural strength and interface micrographs of IPS-Empress II (IPS) inlay-retained fixed partial dentures (IRFPD) reinforced with Zirconia bars (Zb). Materials and methods: In the Finite element analysis, six three-dimensional models of IRFPD were designed using Solid Works 2006. Five models were reinforced with different Zb and a model without Zb was considered as a control. The bridges were loaded by 200 and 500 N forces at the middle of the pontic on the occlusal surface. Subsequently, von Mises stress and displacement of the models were evaluated along a defined path. In the experimental part, 21 bar shape specimens were fabricated from lithium disilicate and zirconia ceramic in three different designs. The zirconia-IPS interfaces and the fractured surfaces of flexural test were observed using SEM. Results. In the connector area, von Mises stress and displacement of the models with Zb under a load of 500 N were decreased compared to the model without the Zb; however, this difference was not considerable at a load of 200 N. In the mesial connector, Von Mises stress and displacement was decreased from 12.5 Mpa for the control model tested at 500 N to 7.0 Mpa for the model with Zb and from 0.0050–0.0041 mm, respectively. SEM analyses showed that, before fracture, interfacial gaps were not observed along the interfaces, but initiated cracks propagated along the interfaces after flexural loading. Conclusion: IPS IRFPD reinforced by Zb can tolerate higher stresses while still functioning effectively and the interfaces may have desirable adaption.

Influence of implant-abutment connection mode on stress distribution in peri-implant bone

To investigate the influence of butt joint connection and platform switching design of implant-abutment connection on the stress distribution in peri-implant bone. Three-dimensional finite element models of implant-supported mandibular first molar with different implant-abutment connections were computed by COSMOSM 2.85. Traditional butt joint connection was used in model A and platform switching design in model B. Loading conditions were a vertical load of 200 N and inclined load of the same magnitude at 45 degrees to the vertical axis of the implant. Stress distribution in peri-implant bone and von Mises stresses at the same point of buccal and lingual implant-bone interfaces in two models were compared. Stresses concentrated in peri-implant cortical bone at the neck of implants on the buccal and lingual sides; maximum von Mises stresses under inclined load were higher than those under vertical load. Maximum von Mises stress in bone was 11.61 MPa in model A and 7.15 MPa in model B under vertical load, and 22.07 MPa in model A and 11.87 MPa in model B under inclined load respectively. Von Mises stresses decreased as the distance from implant-abutment junction increased and the most obvious change occurred at the interface between cortical bone and spongy bone. Von Mises stresses at the same points of buccal and lingual implant-bone interfaces in model A were higher than those in model B. Compared with butt joint connection, platform switching design improved the stress distribution and decreased the maximum stresses in peri-implant bone around implant cervix.