Computer Methods in Biomechanics and Biomedical Engineering

Intracranial aneurysm is a cerebrovascular disorder that weakens the intima of the cerebral artery or vein causing a local dilation of the blood vessel after which the blood vessel becomes thin and ruptures without warning. The resultant bleeding into the space around the brain is called subarachnoid hemorrhage (SAH). In this context, there is an urgent need for early aneurysm rupture prediction that could save numerous human lives. Computational fluid dynamics (CFD) has proved to be potent enough for the prediction of intracranial aneurysm rupture. The computational analysis along with the expertise in numerical methods for the virtual prediction of complicated life-threatening medical disorders is essential to be focused for the betterment of society. In this research, we aimed to predict the rupture of intracranial aneurysm through different morphological parameters of the aneurysm and changes in hemodynamics obtained from CFD. The various treatment options for intracranial aneurysm involves endovascular clipping, coiling and both coiling and stenting. We demonstrated quantitatively and qualitatively the hemodynamic changes (velocity, pressure, and wall shear stress—WSS) in artery after stent implantation and coiling into the 3D reconstructed patient-specific artery model, taking into consideration the non-Newtonian characteristics of blood using finite element approach. We also performed a comparison between scenarios of aneurysm and normal artery without aneurysm, which showed considerably high WSS, pressure, and velocity values in the model with aneurysm. The possible treatment options for the case were also computationally analyzed with the fluid structure interaction (FSI) which showed stenting and coiling considerably reduced the WSS on the aneurysm dome. It was speculated that low WSS at the tip of the aneurysm and high WSS on the aneurysm dome is responsible for the rupture of aneurysm.

Obstructive sleep apnea syndrome (OSA) is the hindrance of upper airway during sleep, associated with curtailment in blood oxygen saturation. It is characterized by subdual flow of oxygen to vital organs causing irregular heart rhythms. One of the triumphant surgeries to treat OSA is maxillo-mandibular advancement (MMA) which is found to be 90% successful for OSA patients (Phee 2015). In MMA, the lower jaw and the mid-face are progressed to augment the posterior airway space facilitating trouble-free breathing. In this research, we attempted to contemplate the von Mises stresses due to mastication in normal and osteotomed 3D models and identify the maximum stress that can be tolerated by the mandible using finite element analysis (FEA). FEA has been extensively used to solve complex problems in dentistry and researchers have found a high correlation between FEA simulation results and in vitro measurements for mandibular specimens (Erkmen et al. 2005). The location of screws and miniplate fixation in the 3D osteotomed models was determined by Champy’s lines in order to ensure stable fixation (Erkmen et al. 2005). We first evaluated the extent of movement of the posterior airway space that is mandatory for the OSA patients to breathe normally. It was evident that the airway constriction was corrected in the upper respiratory tract by the advancement of the mandible. The von Mises stress and displacement in the mandible before and after MMA by applying three different loads, incisal, contralateral compressive molar loads, and one-sided molar loads were analyzed to rule out the fixation and orthognathic issues. The stress distributions during mastication were furthermore compared for mandibular osteotomy models with two distinct lengths of advancement. In addition, the deflection by virtue of mastication on molars, incisors, and canines was also assessed. In line with the above-mentioned evaluation, we performed the computational fluid dynamics (CFD) analysis of the upper airway model with the pre- and post-surgical conditions to predict the airflow dynamics accordingly.

Soldiers, recreational backpackers, and students are often required to carry their own equipment using backpacks. Shoulder strain is one of the limiting factors of load carriage, due to higher sensitivity for pressure hot spots, and susceptibility to short-term injuries such as soft tissue damage and trapped nerves or obstruction of blood vessels. However, to date, no optimized system is available for heavy load carriage, and the considerations for schoolchildren and students are more fashion-weighted than ergonomics or comfort-weighted.

Mammography is a specific type of breast imaging that uses low-dose X-rays to detect cancer in early stage. During the exam, the women breast is compressed between two plates until a nearly uniform breast thickness is obtained. This technique improves image quality and reduces dose but can also be the source of discomfort and sometimes pain for the patient. Therefore, alternative techniques allowing reduced breast compression is of potential interest. The aim of this work is to develop a 3D biomechanical Finite Element (FE) breast model in order to analyze various breast compression strategies and their impact on image quality and radiation dose. Large breast deformations are simulated using this FE model with ANSYS software. A particular attention is granted to the computation of the residual stress in the model due to gravity and boundary conditions (thorax anatomy, position of the patient inside the MRI machine). Previously developed biomechanical breast models use a simplified breast anatomy by modeling adipose and fibroglandular tissues only (Rajagopal et al. in Wiley Interdiscip Rev: Syst Biol Med 2:293–304, 2010). However, breast reconstruction surgery has proven the importance of suspensory ligaments and breast fasciae on breast mechanics (Lockwood in Plast Reconstr Surg 103:1411–1420, 1999). We are therefore consider using a more realistic breast anatomy by including skin, muscles, and suspensory ligaments. The breast tissues are modeled as neo-Hookean materials. A physical correct modeling of the breast requires the knowledge of the stress-free breast configuration. Here, this undeformed shape (i.e., without any residual stress) is computed using the prediction–correction iterative scheme proposed by Eiben et al. (Ann of Biomed Eng 44:154–173, 2016). The unloading procedure uses the breast configuration in prone and supine position in order to find a unique displacement vector field induced by gravitational forces. The 3D breast geometry is reconstructed from MRI images that are segmented (Yushkevich et al. in Neuroimage 31:1116–1128, 2006) to differentiate the four main tissue types. The breast volume is discretized with a hexa-dominant FE meshing tool as a unique volume. Finally, the model is evaluated by comparing the estimated breast deformations under gravity load with the experimental ones measured in three body positions: prone, supine, and oblique supine.

A pressure ulcer (PU) is a localized injury of weight-bearing soft tissues, typically over a bony prominence, which develops primarily due to pressure, or pressure in combination with shear.

Physically-realistic models of the face can contribute to development in several fields including biomedicine, computer animation, and forensics. Face models have benefited from better anatomical representation of the mimetic muscles, and more realistic interactions between soft and bony tissues. These models can also benefit from improved characterisation of the skin layer by having more authentic deformation and wrinkling behaviour. The objective of this work is to compare and evaluate the ability of different constitutive models to simulate the mechanical response of facial skin subjected to a rich set of deformations using a probe. We developed a finite element model to simulate facial skin experiments. Several anisotropic constitutive equations were tested for their suitability to represent facial skin. The finite element model simulated the force-displacement response of facial skin under a rich set of deformations. The variance accounted for between the experimental data and model data ranged from 79% for the Gasser et al. (2006) model to 96% for the Bischoff et al. (2002) model. Estimated pre-stresses ranged from 7 kPa in the lip region to 53 kPa in the central cheek region.

The macroscopic growth of brain tumors has been studied by means of different computational modeling approaches. Glioblastoma multiforme (GBM) is the most common malignant type and is commonly modeled as a reaction–diffusion type system, accounting for its invasive growth pattern. Purely biomechanical models have been proposed to represent the mass effect caused by the growing tumor, but only a few models consider mass effect and tissue invasion effects in a single 3D model. We report first results of a comparative study that evaluates the ability of a simple computational model to reproduce the shape of pathologies found in patients. GBM invasion into brain tissue and the mechanical interaction between tumor and healthy tissue components are simulated using the finite element method (FEM). Cell proliferation and invasion are modeled as a reaction–diffusion process; simulation of the mechanic interaction relies on a linear elastic material model. Both are coupled by relating the local increase in tumor cell concentration to the generation of isotropic strain in the corresponding tissue element. The model accounts for multiple brain regions with values for proliferation, isotropic diffusion, and mechanical properties derived from literature. Tumors were seeded at multiple locations in FEM models derived from publicly available human brain atlases. Simulation results for a given tumor volume were compared to patient images. Simulated tumors showed a more symmetric growth pattern compared to their real counterparts. Resulting levels of tumor invasiveness were in agreement with simulation parameters and tumor-induced pressures of realistic magnitude were found.

Unicompartmental knee arthroplasty (UKA) is a clinical option for knee osteoarthritis continuum of care, providing a soft tissue sparing and less invasive approach compared to total knee arthroplasty (TKA). Compared to TKA, a unicompartmental procedure involves reduced blood loss, faster recovery, and fewer clinical complications. When designing new UKA implants, clinical risks must be assessed and mitigated. Implant fracture, while rare clinically, is an important consideration in design, and while design for minimal strength risk can be supported by simulation techniques and physical testing, published guidelines for such evaluations are not currently available. This publication presents a methodology developed in the course of verifying a new UKA tibial baseplate design and combines finite element analysis (FEA), design of experiments (DOE) and bench-top fatigue testing. The FE model and fatigue test setup have a three-point bend configuration which creates peak stress in the region where clinical fractures have occurred. Both FE model and fatigue test leveraged a draft ASTM standard for three-point bend testing of UKA baseplates. FEA and DOE were used in concert to identify a position for applied loading that produces worst-case stress in the implant. Subsequently, fatigue testing was performed on the implant that was analyzed by FEA and it was confirmed that the simulation accurately predicted the fatigue crack initiation site in implants tested to fracture. In recent years, the use of computational modeling to predict clinical performance has drawn the attention of regulatory agencies worldwide, and there is a growing expectation that such modeling must meet certain standards for verification and validation for it to be credible and also applicable to the performance questions it is used to answer. In this case, DOE explores the design environment by using not one but a range of load positions to find a worst-case scenario and to illustrate the sensitivity to model inputs. The bench-top test serves as a validation comparator, showing that the simulation is predictive of the product's physical behavior.

Wound healing is a complex natural response to tissue injury intended to restore the integrity and function of the tissue at the wounded site. The wound healing process occurs naturally under physical/mechanical forces, e.g., local stretching, and in many cases, benefits from application of applied remedies. Identification of potentially effective compounds requires specialized approaches to determine their effects on different cell types. However, working in vivo has quantification limits and ethical concerns arise. This is especially true for natural origin compounds, such as plant extracts, honey, and larvae, which have a complex composition and determining their clinical efficacy is challenging. Thus, in vitro gap closure assays can be used to evaluate the effects of natural treatments and external strains on migration associated with gap closure. Here, we evaluate the changes in cell migration during gap closure in vitro, following treatment with honey and/or under applied external strains. We generated monolayers of NIH3T3 mouse fibroblasts and induced a small gap (wound) at their center. Using custom image processing modules, we measured the kinematics of the gap closure, focusing on times of initiation and rates of migration. We evaluated the effects of different concentrations of a well-known natural wound-care agent, i.e., honey. Honey has been used in skin wound care for many years due to its anti-inflammatory, antimicrobial, and cell-stimulating properties. Using our assay we are able to show the direct effects of honey on the migratory capabilities of the cells and the kinematics of gap closure. In addition, we evaluate the effects of externally applied stretching, with and without the addition of natural remedies, on the gap closure process. For this, we grow the cell monolayer on an elastic, stretchable membrane, which is then stretched in varying levels using a 3-D printed cell stretching apparatus. We evaluated the effects on gap closure kinematics of different levels of externally applied strains, showing that low (3%) strains may accelerate gap closure, while higher (6%) strain may not be as efficient, relative to unstretched control. Thus, combining external deformation with various treatments can enhance the rate of migration and thus shorten the time required for wound healing.

Ultrasensitive Doppler is a recent medical imaging technique enabling high sensitive acquisition of blood flows which can detect small vascular features without contrast agents. Applied to cerebral tomographic imaging of rodents, this method produces very fine vascular 3D maps of the brain at high spatial resolution of 100 μm. These vascular networks contain characteristic tubular structures that could be used as landmarks to localize the position of the ultrasonic probe and take advantage of the easy-to-use property of ultrasound devices. In this study, we propose a computational method that performs 3D extraction of vascular paths and estimates effective diameters of vessels, from ultrasensitive Doppler 3D reconstructed images of the rat brain. The method is based on the fast marching algorithm to extract curves minimizing length according to a relevant metric.

Valve diseases are more and more treated with transcatheter aortic valves. This work is based on an experimental setup with the corresponding fluid–structure interaction model to show the feasibility of performing accurate simulations which is able to capture the main behavior of a transcatheter valve both from structural and fluid dynamic points of view. The application of this methodology to patient-specific cases is also illustrated.

We review several of our mathematical models that we constructed for the simulation of contractures and morpho-elastic scars that are typically associated with deep dermal (burn) injuries. The models are based on partial differential equations, which are solved by the use of finite-element methods. The models contain elements of non-isotropy, morpho-elasticity for the treatment of the mechanics of the skin. Furthermore, we take into account the balances of fibroblasts, myofibroblasts, collagen and a generic growth factor. Using the models, we are able to simulate permanent contractions using physically sound principles.

Disc herniation is one of the main causes of low back pain, and it is the pathologic condition for which spinal surgery is most often required. Many experimental and numerical studies have been conducted to investigate the mechanical failure of the intervertebral disc (IVD); however, there is not in the literature a study that defines a mechanical criterion for the disc failure. The aim of this study was to investigate the state of stress generated by the application of high loads and to define which state of stress was the most responsible for herniation. A finite element model of the ovine lumbar IVD was developed. The loading scenarios applied in an experimental study taken from the literature were applied, and the results compared to define the failure conditions. Then the effect of combined and simple rotations was investigated as well. It was found that an axial stress higher than 10 MPa in the posterior region of the annulus has a high probability of damaging the disc, and that flexion had a main role in damaging annulus tissue.

In this study, the movement of climbing a step is decomposed in 4 EOS images. A patient-dependent 3D model of the knee is then created from MRI, and several numerical simulations are carried out according to the experimental boundary conditions (force and flexion angle), so as to ensure the global knee mechanical equilibrium. To validate this patient-specific model, its bony structure is confronted with the EOS images once the mechanical equilibrium is reached. This model gave us an estimation of the stress in the ligaments for every flexion angle as well as a pressure map on the cartilages.

Although it is long accepted that aseptic loosening is the main reason for revision of total joint replacements, preclinical assessment methods of primary fixation are not well developed. Reasons for aseptic loosening are multifactorial including the patient, surgical approach, biological reactions, wear, micro-motion at the implant–bone interface, load transfer from the joint to the host bone, and bone adaptation. The objective of this study was to highlight a few preclinical methods to investigate orthopaedic implant primary fixation relative to the transfer of loads and displacements at the implant–bone interface. The last generation of metal-on-metal hip prostheses used a high-precision low clearance bearing to provide a low friction ball and socket joint. During implantation the acetabular component deforms under a press-fit; however, excessive deformation of the acetabular component can lead to premature failure of the joint replacement. It is therefore important to establish an accurate method of quantifying cup deformation and develop finite element models to better understand the effects of the press-fit. Methods to measure press-fit deformation of monoblock acetabular cups for metal-on-metal total hip arthroplasty and resurfacing were investigated. The purpose of the present study was to compare cup deformation with two experiments simulating press-fit of an acetabular cup into the pelvis. Rim deformation and cup strain were measured for two common tests: (1) a two-point pinching of the cup rim and (2) a press-fit implantation into a cavitated polyurethane foam block. In the pinch test, the rim displaced linearly and symmetrically with force. The press-fit test, ostensibly a closer representation of surgical procedure, produced more complex displacement and strain responses due to the foam block shape, and the cup surface-foam block interaction. The current study demonstrated two methods to measure real-time hip cup deformation and strain during press-fitting that may be used for preclinical assessment of primary fixation.

The rate of healing and rehabilitation in fractures of the feet depends on the level and the program of loading the damaged segment. The paper studied the possibilities of efficiently controlling the unloading level of the affected area by varying the degree of orthosis tightening (lateral compression). Among others, a hypothesis was tested‚ according to which only in a slip the limb by increasing the lateral compression is pushed up and the coefficient of unloading (CU) grows. Two types of shin-orthosis system models were developed and studied numerically for different variants of parameters: conical models using the package, based on boundary integral equation method and BEM, and personalized real form models based on the technology «CT scan –> Specialized processing software (Mimics) –> FEA package». The unloading coefficient dependence on the circumferential tightness for two types of “slippery” stocking materials was measured. When using both synthetic and silk stockings‚ experimental results did not show valid growth of CU with an increase in tightening (lateral compression) neither while standing nor walking. As calculations showed, pushing the shin up due to lateral compression may be to a maximum of ~ 1.2 mm even in total slip. At the same time‚ the shift of the shin surface as a result of the piston effect can reach several mm. Thus, the additional sediment due to the so-called “piston effect” (skin stretching under a load, as well as its shift-slip over thin and soft layer of subcutaneous fat) is several times greater than the effect of ejection due to lateral compression and associated unloading, and thus completely reduces them to nothing. Further possibilities and approaches to the problem of load programming at limb orthotics are discussed.

In recent years, it has been suggested that statistical shape model based 2D–3D reconstruction of the proximal femur could offer a solution to issues with preoperative planning of total hip replacement from 2D radiographs. The purpose of this work was to assess the effect of radiographic femoral rotation on the accuracy of a statistical shape model based 2D–3D femoral reconstruction method. A reconstruction algorithm was tested on input images with varying amounts of internal/external rotation (10 internal to 50 external) using leave-one-out tests and the resulting 3D shape was compared to the CT segmentation by point-to-point distance. The minimum value for mean point-to-point error was 1.24 ± 0.18 mm and occurred at 20º of external rotation (where neutral orientation was the femoral neck axis aligned in the coronal plane). The maximum error calculated was at 50º of external rotation with mean point-to-point error being 1.88 ± 0.41 mm. This work highlights an important source of error for 2D–3D reconstruction algorithms which may be incorporated into future validation studies.

Assessment of myocardial damage is important to obtain an accurate prognosis after myocardial infarction. Myocardial strains have been shown to be good indicators of the myocardial viability. Strain analysis has been used to identify dysfunctional regions, and several strain-based parameters have been proposed to detect regions of infarct. In this study, nine different parameters were used to detect synthetically generated infarct lesions on left ventricles and their performances were compared. The parameters were investigated on ten virtual 3D cases based on healthy human left ventricles extracted from MRI examinations. Realistic infarcts were generated for each virtual case with different locations, shapes, sizes, and stiffer materials. Diastolic virtual strain data were obtained via finite-element simulations using widely implemented constitutive law and rule-based myofiber orientation. The results showed that stretch-dependent invariance in fiber direction is able to better delineate the infarcts in comparison to the other parameters.

Glucose transport in fat cells results in accumulation of triglycerides in lipid droplets and is regulated by insulin. When a fat tissue becomes insulin-resistant, glucose transport into the cells is impaired and results in Type 2 diabetes. The lipid droplets accumulation is part of the adipogenesis differentiation and metabolism. In the current study, we monitored the adipogenesis of 3T3-L1 cultured cells in high and low glucose concentrations, while the cells were exposed to different substrate rigidity and tensile deformation. Phase contrast images were taken along the adipogenesis process and were analyzed by a new MATLAB image processing algorithm, based on a previous code written in our group (Levy in Annals of biomedical engineering 40:1052–1060, 2012). The new algorithm follows cell differentiation (cell size and morphology and nucleus size) and lipid accumulation (number of lipid droplets per cell and their radius). Complementary, we analyzed by immunofluorescence (IF) the molecular expression of PPARγ, a transcription factor, along with DNA staining by DAPI and Lamin A/C for the nucleus organization. The results indicate that high glucose concentration and substrate tensile strains delivered to adipocytes accelerate their lipid production. In addition, the cell and nucleus area and cell morphology change during the differentiation process.

In this study, experimental electroporation model with human aorta tissue is compared with computational modeling. The segments in native state of the aorta are treated by electroporation method through a series of electrical impulses from 50 to 2500 V/cm. The Pennes Bioheat equation is used to solve heat transfer problems. Different conductivity values are used in order to fit the experimental results. It has been shown that there are a smaller number of vascular smooth muscle cells (VSMC) nuclei at the tunica media, while the elastic fibers morphology is maintained 24 h after electroporation. Additionally we studied with computational model of plaque formation and progression the reduction of the plaque size with electroporation. The initial results have been shown plaque reduction for carotid artery case. Future studies are necessary for design of a new device for in vivo ablation with electroporation of plaque stenosis.

Stereotactic procedures are an increasingly common tool for the diagnosis and treatment of neurological disorders. Common surgeries reliant on a stereotactic reference frame include Deep Brain Stimulation, Stereoelectroencephalography, Stereobiopsy, and high precision intraparenchymal drug delivery. Introduction: Stereotactic neurosurgical procedures are planned and carried out per preoperative medical images in a fixed reference frame. Loss of cerebrospinal fluid and a variety of other factors lead to a displacement of the anatomical target from the stereotactic coordinates, known as brain shift. Aims: To develop a computational model to aid in the understanding and prediction of gravity induced brain shift based on patient repositioning. Methods: The MNI ICBM152 Average Brain Stereotaxic Registration Model was manually segmented and meshed in the Simpleware Scan IP software package. Using FEBio, suitable constitutive models were applied to each region. The model was then loaded to simulate supine-to-prone repositioning. Results: Displacement reached a maximum of approximately 2.4mm, with cortical displacement being concentrated in anterior regions. Conclusions: With good initial results, the future applications of this method appear promising.

Blood pressure drop and arterial distensibility are important, allegedly independent, parameters that are indicative of the coronary arteries patency and atherosclerosis severity. In the present study we show that these two parameters are dependent, allowing to obtain both parameters from a single measurement, and to do so a high-resolution differential pressure measurement system is required. The objective of the study was to unveil the relationship between local fluid pressure drops and tube distensibility, through various scenarios of stenosis severity, tube diameter, and flow rate (for coronary hemodynamic conditions). The investigation was performed using validated Fluid–Structure Interaction (FSI) analysis on silicone mock arteries with intermediate size stenosis (0–65%). Highly accurate pressure drop measurements (±0.05 mmHg) were performed with our in-house fluid-filled double-lumen catheter measurement. The results indicated that our accurate pressure drop measurement method facilitated the differentiation among several levels of the mock arteries’ stiffness, with distensibilities ranging from 1 to 7%. Local pressure drops were markedly affected by the mock arteries’ stiffness and could be best described using a second-order polynomial function. These changes in pressure drop could be detected even when there was no stenosis present, and FFR values remained insensitive at 1.00. The results indicated the clinical potential of a high accuracy pressure drop-based parameter to be superior to FFR. Such a parameter would provide cardiovascular interventionalists with lesion-specific bio-mechanical and functional data, for improved real-time decision-making in the cath-lab.

Background Ankylosing spondylitis (AS) is a chronic inflammatory disease primarily affecting the axial skeleton, including the sacroiliac joints, costovertebral joints, and the spine. Patients with AS found to have an alter gait pattern. The purpose of this study was to investigate biomechanical alterations in gait after surgical correction in a patient with severe kyphosis from AS. Methods A case report in controlled laboratory study, a pretest–posttest design. A 20-year-old male presented with severe sagittal imbalance and inability to stand erect due to AS. He presented with thoracic kyphosis of 70°, lumbar kyphosis of 25°, and pelvic incidence of 43°. The patient had a complex spinal reconstruction with 84° of sagittal correction, normalizing his sagittal alignment. Gait analysis was performed the day before surgery and 1 month post surgery, including three-dimensional kinematics, ground reaction forces, and electromyography outcomes. Results Normalization of spinal alignment minimally increased walking speed and cadence. Lower extremity ranges of motion angles increased but were not symmetrical even 1 month post surgery. Postoperatively, trunk flexion, neck extension, and head orientation angles decreased compared with preoperative values but was not symmetrical even 1 month post surgery. The trunk muscles were activated earlier in the post-surgery condition compared to the pre-surgery condition while lower extremity muscles presented later muscle activation. Conclusions Surgical correction of spinal alignment improved spine function and efficiency. Changes in gait abnormality parameters observed imply that the patient used less energy to ambulate after surgery than before surgery. Although pre-surgery data showed compensation in the spine kinematics, post-surgery data supported significant changes in the spine and the lower extremity values.

Adult degenerative scoliosis results from age-related changes leading to segmental instability, deformity, and stenosis. Patients with degenerative adult scoliosis demonstrate an altered gait pattern. Use of a walker tends to cause a more kyphotic posture due to its lower hand grips, and due to the way patients must reach forward with this position using both hands, forcing a kyphotic moment into their gate cycle. Whereas a walker forces patients into kyphosis, the higher grips of walking sticks allow for more upright posture and improved sagittal alignment. The purpose of this study is to compare and contrast the benefits of walking sticks versus a walker on the biomechanics of the lower extremity in people with degenerative scoliosis, as evaluated by gait analysis. Ten patients with symptomatic degenerative scoliosis have been deemed appropriate surgical candidates. Each patient performed a series of overground gait trials with a comfortable self-selected speed under three testing conditions: 1. with walking sticks, 2. with a walker, and 3. without any device. The use of walking sticks resulted in significantly slower, longer stride and step times along with bigger ankle, knee, and hip flexion range of motions in comparison to the walker. Walking sticks did improve the biomechanics and did facilitate positioning of the trunk and lower extremity during walking in adult degenerative scoliosis patients.

Purpose: To investigate the effect of adjacent load transfer pre- and post-fusion surgery of lumbar scoliotic spines using FE models. Methods: Ten three-dimensional nonlinear FE models of the lumbosacral spine were created from pre- (Cobb angle: 28.1° ± 10.5°) and post-scoliosis surgery and healthy in vivo CT scans. During surgery, pedicle screws and rods were implanted at lumbar and sacral levels. A compressive load and six different moments (flexion, extension, lateral bending, and axial rotation) were applied to the top level of each model. Outcome measures were range of motion (RoM), intradiscal pressure (IDP), and facet joint forces (FJF). Results: Spinal fusion did alter the mechanical function of the scoliotic spine. Scoliotic spine presented abnormal and asymmetrical kinetic and kinematic behavior in comparison to a healthy spine. After the fusion surgery, RoM decreased by 91.88 %, IDP decreased by 46.87 %, and FJF decreased by 60.63 % at the fused level on average whereas a minor increase of RoM, IDP, or FJF was observed at the adjacent level. Compared to the healthy subjects, the pre-surgical scoliosis subjects have up to 8.03 % greater RoM, 20.04 % increased IDP, and 18.38 % increased FJF on average at the adjacent level. Conclusions: This study was the first to investigate the effect of adjacent load transfer before and after fusion surgery using in vivo CT scans of ten scoliotic spines. A posterior fusion has only a minor effect on mechanical behavior and large effect on pressure and forces at the adjacent level. As expected, a large effect on the kinematics and kinetics was found at the fused level.

The present study introduces a quantitative and methodological tool for assessing the effectiveness with which ballistic helmets protect the brain and optic nerve against non-penetrating projectile impacts. A three-dimensional finite element biomimetic head model with different ballistic helmets was used for this purpose.

Closure of large soft-tissue defects following surgery or trauma constitutes substantial but common reconstructive challenges. Closing the wounds with sutures is a common solution yet involving high-tension closure. The alternative methods of closure such as skin grafting are often associated with relatively more complex surgical procedures, significant morbidity, and extended hospitalization and recovery periods. Here, we evaluate the efficacy of a tension relief system (TRS) device and compare it to surgical sutures. We employed finite element modeling and simulated three cases of (real) large wounds which were treated with TRS in reality, each located in a different organ and has different dimensions. Closure of the wounds induced peak-effective stresses on the skin that were at least an order of magnitude greater (and sometimes nearly 2 orders of magnitude greater) than when tension sutures were used with respect to the corresponding TRS data. For the tension suture simulations, the tensile stress was in the range of 415–648MPa and in the TRS simulations, it was 16–30MPa. Such large localized tissue distortions may obstruct the vasculature surrounding the wound or at the sutured skin itself, which will cause ischemia and necrosis of the skin within several hours following surgery. In addition, the substantial reduction of loads on and within the skin during large wound closure by the TRS allows surgeons to optimally employ the viscoelastic properties of the skin for primary wound closure.

Pedicle Subtraction Osteotomy (PSO) is a technique for restoring the correct sagittal balance that achieves corrections up to 35°. The procedure still shows a high rate of complications (10–25%, usually rod breakage at the osteotomy level): in order to decrease this rate a computational comparative analysis investigating the effects of a set of variables on the instrumentation has been set up. In particular the number of rods, the material, the diameter, and the presence of an anterior support have been considered in an FE model of L1-S1 simulating a PSO at either L3 or L4. Standing was simulated using a follower load of 500 N and pure moments of ± 7.5 Nm in flexion, extension, lateral bending, and axial rotation evaluating the load sharing between the anterior part of the spine and the rods and the stress in the rods. Analyzing our results we can suggest the use of a multiple rod configuration, associated with the use of an anterior support in order to reduce the stresses on the instrumentation.

Serial Ponseti casting occasionally fails to completely correct idiopathic clubfoot deformities and recurrence of deformity occurs. As these bones are largely unossified, statistical shape modelling (SSM) from MRI considers the entire set of shape features simultaneously and may provide a more accurate assessment of differences in bone morphology between two groups. The purpose of this study was to compare the shape of the talus in normal and clubfeet using direct geometric measurements and SSM. Both methods found significant differences between the control and clubfoot groups.

Soft biological tissues vary significantly in their mechanical properties, from the more rigid articular cartilage to the very soft and extensible skin and mesentery. Yet tissues are made of the same constituents: Fibers, muscle cells, non-muscle cells, and a fluid matrix. The key to diversity in properties is a parallel diversity in structure. The present study addressed the question of how is tissue structure determined? Living tissues have the unique ability to grow and remodel under altered mechanical loading by turnover of their fibers, where some are degraded and new ones are produced and deposited. It was hypothesized that tissue structure evolves with growth by remodeling its structure in response to growth-induced loading. The hypothesis was tested by structural simulation. The modeling framework developed is a multi-scale, micro-mechanical one, which integrates the effects of cells, fibers, and matrix, based solely on the biological processes in the remodeling tissue, thereby linking the constituents’ turnover to the evolving tissue structure and properties. The results are compatible with the evolved adult tissue structure and mechanical characteristics. Specifically, the theory predicts the evolution of well-known soft tissues features such as the nonuniform undulation of collagen fibers and associated tissue, nonlinear convex strain–stress response, and the evolution of growth-induced prestrain and prestress. These results support the notion that tissues’ structure and properties evolve as they grow.

The main cause of cancer-related deaths is metastasis-spreading of cancer cells to different sites in the body. A critical step in metastasis formation is invasion of cells through the surrounding tissue. During invasion, cancer cells change their shape and apply forces. We have previously identified that about 30% of single, metastatic, breast cancer cells will indent impenetrable synthetic, non-degradable, polyacrylamide gels, when gel stiffness is in the range 1–10 kPa. By measuring the depth of indentation of an initially flat gel and monitoring time-dependent microscopic changes in cell morphology, we were able to distinguish between benign and metastatic cells, also identifying their metastatic potential (MP); benign cells do not indent the gels. Recent works have indicated that metastases from solid tumors occur predominantly by collective cell invasion. Hence, in the current study we evaluate the mechanical interactions of cell clusters with the impenetrable gel. We observe that indenting subpopulations of metastatic cells are doubled in clusters, and cells are also indent more deeply; this increases likelihood to successfully form metastasis in the body. Concurrently, double the fraction of high MP cells indent gels as compared to low MP cells, while benign cells do not indent even in clusters. We also show that the gel platform can be used to determine the time-dependent impact of chemotherapeutics on the cells’ ability to apply forces and indent gels. Our approach can provide a rapid, mechanical prediction of the likelihood for invasiveness of cancer cells and can further be applied in a patient-specific approach, thus providing a personalized prognosis that may improve treatment of cancer patients and increase their life expectancy.

Despite the promising outcomes of transcatheter aortic valve replacement (TAVR), adverse events may occur as a result of suboptimal placement. The aim of this study is to evaluate the effect of various TAVR deployment positions on the risk for intra-procedural migration and of post-procedural paravalvular regurgitation. Finite Element (FE) and Computational Fluid Dynamics (CFD) models are presented for several procedural scenarios for a patient-specific morphology. Crimping and deployment of balloon-expandable Edwards SAPIEN were modeled in three locations. The proximal deployment resulted in higher risk for migration, while the distal and midway positioning resulted in comparable outcomes. These resulting configurations were used to assess diastolic hemodynamics. The distal case had preferred hemodynamics compared to the midway with more limited leakage. The proposed approach has the potential to be used in procedural planning to ultimately achieve better clinical outcomes.