Biomechanical analysis of osteoporotic spines with diseases using CT-based finite element method

The eventuality of recurrent fractures on the adjacent level of fractured vertebra is becoming prevalent in this era. To date, the underlying cause of this phenomena is either due to low bone quality or adverse geometrical changes of the vertebral body, as a result of osteoporosis and vertebral compression fractures (VCFs). To further investigate the determinant factor of this phenomenon, an image based finite element analysis (FEA) was used to scrutinize the biomechanical response of spines that have been afflicted by different types of spinal deformities, namely; wedge-shaped, fish-shaped and plana-shaped vertebrae. The evaluation was made based on its structural integrity in accordance to stress and strain distributions, and fracture risks prediction. These findings were then further corroborated by evaluating other associating factors such as kyphotic deformity angle and bone density distribution in order to find the underlying cause of this symptom. The results showed that the low bone density due to osteoporosis has become the dominant factor in inciting the risks of subsequent fractures on the adjacent vertebrae. This is based on the contradictory relation between the number of the failure elements distributions and the degree of the kyphotic deformity angle, as described by the wedge-shaped vertebral fracture model. Obviously, the most highly structural deformed vertebra still could withstand any kinds of high input loads, provided that its structural formation is still intact and has not severely affected by osteoporosis. The high incidence of subsequent fractures following Balloon Kyphoplasty (BKP) in both the augmented and adjacent vertebrae is quickly becoming a clinically unresolvable complication. The underlying cause of this phenomenon is still unknown and to date medical practitioners are still unable to explain the fundamental cause of this phenomenon. To verify this claim, an image-based finite element analysis was used to investigate the effectiveness of BKP treatment of pre-operative and post-operative osteoporotic spine models. The three-dimensional (3D) non-linear finite element (FE) models of the thoracolumbar spine (T11-L3) were developed from CT-scan images. The biomechanical responses were evaluated based on the models’ load sharing mechanisms, load transfer mechanisms, stiffness recovery, stability, and kyphotic deformity restoration. The margin of safety for each of the models was evaluated under incrementally increased loads (1-10kN). This margin would be determined based on the fracture risk evaluation in accordance to the associated onset fracture load. The results showed that the BKP procedures play a significant role in enhancing the structural integrity of the treated spine by lowering the effect of the bone fracturing and optimizing the biomechanical alterations up to its pre-fracture level. However, the phenomenon of high incidence of vertebral bone failures on the augmented and its neighboring vertebrae indicates that the osteoporosis severity is the most influential factor in determining the sufficiency of the BKP treatment. Cage subsidence, pedicle screw loosening and instability are the most prevalent posterior lumbar interbody fusion (PLIF)-related complications. These may be attributed to interrelated mechanical, biomechanical and environmental factors. Current advancement in medical treatment has paved the way for the implementation of unilateral cages in an oblique position to overcome unintended mechanical and clinical shortcomings. To verify this claim, an imagebased finite element analysis (FEA) was used to evaluate several factors; cage subsidence, screw loosening and PLIF construct stability via stress profiles, fracture risk prediction and range of motion (ROM) evaluations in the different type of cage materials and cage orientations. Obviously, obliquely-placed unilateral fusion cage constructs with PI exhibited the most reliable biomechanical constructs by showing the smallest ROM and producing the minimal distortion stress at the cage-endplate and pedicle screw-bone interfaces. Moreover, these results also showed good agreement with the results obtained using fracture risks assessments by showing the lower numbers of deformation elements at the both contact interfaces in normal and traumatic events. In conclusion, biocompatible cage materials and structural symmetry are the most important criteria in achieving biomechanical advantage in PLIF surgery

Biomechanical analysis of sandwich vertebrae in osteoporotic patients: finite element analysis

ObjectiveThe aim of this study was to investigate the biomechanical stress of sandwich vertebrae (SVs) and common adjacent vertebrae in different degrees of spinal mobility in daily life.Materials and methodsA finite element model of the spinal segment of T10-L2 was developed and validated. Simultaneously, T11 and L1 fractures were simulated, and a 6-ml bone cement was constructed in their center. Under the condition of applying a 500-N axial load to the upper surface of T10 and immobilizing the lower surface of L2, moments were applied to the upper surface of T10, T11, T12, L1, and L2 and divided into five groups: M-T10, M-T11, M-T12, M-L1, and M-L2. The maximum von Mises stress of T10, T12, and L2 in different groups was calculated and analyzed.ResultsThe maximum von Mises stress of T10 in the M-T10 group was 30.68 MPa, 36.13 MPa, 34.27 MPa, 33.43 MPa, 26.86 MPa, and 27.70 MPa greater than the maximum stress value of T10 in the other groups in six directions of load flexion, extension, left and right lateral bending, and left and right rotation, respectively. The T12 stress value in the M-T12 group was 29.62 MPa, 32.63 MPa, 30.03 MPa, 31.25 MPa, 26.38 MPa, and 26.25 MPa greater than the T12 stress value in the other groups in six directions. The maximum stress of L2 in M-T12 in the M-L2 group was 25.48 MPa, 36.38 MPa, 31.99 MPa, 31.07 MPa, 30.36 MPa, and 32.07 MPa, which was greater than the stress value of L2 in the other groups. When the load is on which vertebral body, it is subjected to the greatest stress.ConclusionWe found that SVs did not always experience the highest stress. The most stressed vertebrae vary with the degree of curvature of the spine. Patients should be encouraged to avoid the same spinal curvature posture for a long time in life and work or to wear a spinal brace for protection after surgery, which can avoid long-term overload on a specific spine and disrupt its blood supply, resulting in more severe loss of spinal quality and increasing the possibility of fractures

Patient specific finite volume modeling for intraosseous PMMA cement flow simulation in vertebral cancellous bone

Ph.DDOCTOR OF PHILOSOPH

Hip fractures : A biomechanical analysis of fracture strength prediction, prevention, and repair

Due to the aging population, hip fracture incidence has been increasing over the past decades. Measurements of bone mineral density with dual energy X-ray absorptiometry are the gold standard for hip fracture risk assessment, where patients with a low bone density have a high risk of fracture. However, many people that are not diagnosed to be at risk, still fracture their hip. Calculations of bone strength using subject-specific finite element (FE) models, can improve fracture risk prediction, but further improvement is required.Patients with a high fracture risk are often prescribed pharmaceutical treatment in order to increase bone density systemically. As systemic response to treatment is limited, other options to prevent fractures by improving the bone strength are investigated. One of those options is the injection of biomaterials in the femoral neck. In case of a hip fracture due to a low-energy fall, total hip replacement is generally preferred over joint-preserving methods like fixation using a dynamic hip screw. Screw fixation comes with a risk of screw instability, especially in low-density bone. Bone cements can be used to improve fixation of orthopaedic implants and fracture fixation devices. Calcium sulphate/hydroxyapatite (CaS/HA) is an injectable biomaterial that has been used, for example, to reinforce collapsed vertebrae and to stabilize wrist fractures. The work presented in the thesis aims to improve fracture risk prediction, and fracture prevention and repair methods with use of CaS/HA. This is achieved through a combination of experimental mechanical tests at organ and tissue scale, and development and thorough validation of FE models of the proximal femur.In the first part of this thesis, 12 cadaveric femora were used in an experiment where the bones were loaded until fracture in a configuration developed to replicate a fall to the side. During loading, high-speed cameras were used to image both the medial and lateral side of the femoral neck allowing for full-field strain measurements using digital image correlation. The femora were imaged with clinical CT before and micro-CT before and after mechanical testing. Using the acquired CT images, FE models were developed at two different resolutions to determine their ability to capture the fracture force, fracture location and surface strains. The FE models based on the clinical CT images were able to accurately capture the fracture force and identify regions where the bone would fracture. These models could also capture the strains with high accuracy. However, the strains were not predicted as accurately in regions with high surface irregularity. The models based on the micro-CT images could show with higher accuracy how the strains were distributed around local porosity (e.g., due to vascularization) in the femoral neck and how these influenced the fracture pattern.The thesis continues with an investigation of fracture prevention and repair methods through the use of CaS/HA. The ability of CaS/HA to increase the fracture strength of the proximal femur for fracture prevention and its ability to stabilize a dynamic hip screw used for fracture repair was investigated. The increase in fracture strength was investigated using FE models. These models showed that CaS/HA can increase the fracture strength of the femur approximately 20% when injected close to the cortex in the lateral neck. Pullout tests using a dynamic hip screw were performed on synthetic bone blocks and femoral heads from hip fracture patients. In the synthetic blocks, CaS/HA significantly increased the pullout strength. However, in the human bone the stability of the screw was not improved, because the cement could not easily spread into the threads of the screws. The mechanical behaviour of CaS/HA and bone was further investigated using high-resolution synchrotron X-ray tomography. Cylindrical trabecular bone specimens with and without CaS/HA were imaged with tomography during in-situ loading of the samples. The images revealed that CaS/HA reinforced the bone, and that CaS/HA is a brittle material that will crack before the bone.To conclude, in this thesis FE models are presented showing accurate prediction of fracture strength, which can be used for improved fracture risk assessments. Furthermore, the work provides insight in how CaS/HA behaves mechanically and how it can be used to increase the fracture strength and to stabilize fixation devices in the femur, improving fracture prevention and fracture repair methods

Osteolytic vs. Osteoblastic Metastatic Lesion: Computational Modeling of the Mechanical Behavior in the Human Vertebra after Screws Fixation Procedure

Metastatic lesions compromise the mechanical integrity of vertebrae, increasing the fracture risk. Screw fixation is usually performed to guarantee spinal stability and prevent dramatic fracture events. Accordingly, predicting the overall mechanical response in such conditions is critical to planning and optimizing surgical treatment. This work proposes an image-based finite element computational approach describing the mechanical behavior of a patient-specific instrumented metastatic vertebra by assessing the effect of lesion size, location, type, and shape on the fracture load and fracture patterns under physiological loading conditions. A specific constitutive model for metastasis is integrated to account for the effect of the diseased tissue on the bone material properties. Computational results demonstrate that size, location, and type of metastasis significantly affect the overall vertebral mechanical response and suggest a better way to account for these parameters in estimating the fracture risk. Combining multiple osteolytic lesions to account for the irregular shape of the overall metastatic tissue does not significantly affect the vertebra fracture load. In addition, the combination of loading mode and metastasis type is shown for the first time as a critical modeling parameter in determining fracture risk. The proposed computational approach moves toward defining a clinically integrated tool to improve the management of metastatic vertebrae and quantitatively evaluate fracture risk

Caraterrizzazione biomecannica in vitro di vertebre naturali e trattate

The research aim of the present thesis was to investigate the in vitro biomechanical properties of human thoraco-lumbar natural and treated vertebral body, undergo prophylactic augmentation. To overcome some limitation of the current in vitro test methods, an anatomical reference frame for human vertebrae was formally defined and validated and the effects of in vitro boundary conditions on the strain experienced by vertebral body investigated. Moreover an integrated approach, which incorporated different measurement methods (strain gauges and digital volume correlation) at different dimensional scales was adopted to investigate natural and augmented vertebrae during non-destructive and destructive testing. The effects of prophylactic augmentation were investigated for the first time through digital volume correlation, which allowed to measure the state of strain inside the vertebral body, in the injected cement, and in the bone-cement interdigitated region of vertebrae, including the elastic regime, but also the internal micro-failure mechanisms. Findings showed that augmentation is not associated to a modification of the strain magnitude but rather to a re-arrangement of the higher strain due to an alteration of the load sharing between the trabecular core and the cement region. The most critical region was the interdigitated area, where the initial microdamage gradually spread across the surrounded trabecular bone. Prophylactic augmentation increased in some vertebrae the failure force required to damage the vertebrae, conversely in other case the failure force was lower than in the controls (not-augmented). This variability of the weakening/strengthening effect of prophylactic augmentation seems to support that the effect of augmentation depends on the quality of augmentation itself (amount, localization and distribution of the injected material). It is therefore reasonable to assume that to improve the outcomes of prophylactic augmentation, more attention should be dedicated to the quality of augmentation itself.L'obiettivo principale della tesi è la caratterizzazione biomeccanica di vertebre umani toraco-lombari naturali e sottoposte alla vertebroplastica profilattica. Per superare alcune limitazioni dei test in vitro, è stato per la prima volta definito e validato un sistema di riferimento in vitro per l'allineamento delle vertebre, ed è stato effettuato uno studio sugli effetti sulla distribuzione delle sollecitazioni al variare delle condizioni al contorno più comunemente utilizzate in letteratura. Questo studio si basa su un'approccio integrato che incorpora differenti metodi di misura delle sollecitazioni (estensimetri e digital volume correlation), utilizzati durante i test in campo elastico e a rottura. L'efficacia della vertebroplastica profilattica è stata investigata per la prima volta grazie alla Digital Volume Correlation, che permette di misurare lo stato di deformazione all'interno del corpo vertebrale a livello dell'osso trabecolare, nel cemento iniettato e all'interfaccia osso-cemento, sia in campo elastico che a rottura. Rispetto alle vertebre naturali i risultati mostrano che il trattamento non altera l'entità delle deformazioni bensì le zone di massimo stress, ciò è dovuto ad un'alterazione nella condivizione del carico tra il tessuto trabecolare e il cemento. la zona più critica si ha all'interfaccia osso-cemento, dove ha origine la frattura. In certi casi il trattamento aumenta la resistenza delle vertebre in altri casi la forza di rottura è inferiore a quella del controllo. Questa variabilità nelle prestazioni meccaniche delle vertebre aumentate dipende dalla qualità del trattamento stesso (quantità cemento, posizionamento e distribuzione)

A computational analysis of a novel therapeutic approach combining an advanced medicinal therapeutic device and a fracture fixation assembly for the treatment of osteoporotic fractures: Effects of physiological loading, interface conditions, and fracture fixation materials

: The occurrence of periprosthetic femoral fractures (PFF) has increased in people with osteoporosis due to decreased bone density, poor bone quality, and stress shielding from prosthetic implants. PFF treatment in the elderly is a genuine concern for orthopaedic surgeons as no effective solution currently exists. Therefore, the goal of this study was to determine whether the design of a novel advanced medicinal therapeutic device (AMTD) manufactured from a polymeric blend in combination with a fracture fixation plate in the femur is capable of withstanding physiological loads without failure during the bone regenerative process. This was achieved by developing a finite element (FE) model of the AMTD together with a fracture fixation assembly, and a femur with an implanted femoral stem. The response of both normal and osteoporotic bone was investigated by implementing their respective material properties in the model. Physiological loading simulating the peak load during standing, walking, and stair climbing was investigated. The results showed that the fixation assembly was the prime load bearing component for this configuration of devices. Within the fixation assembly, the bone screws were found to have the highest stresses in the fixation assembly for all the loading conditions. Whereas the stresses within the AMTD were significantly below the maximum yield strength of the device's polymeric blend material. Furthermore, this study also investigated the performance of different fixation assembly materials and found Ti-6Al-4V to be the optimal material choice from those included in this study

Spinal aging

The age distribution of the global population is shifting upwards. As a result, clinicians worldwide are faced with an increasing number of spinal disorders related to the elderly and spinal aging. Spinal pathology in the elderly specifically includes osteoporosis and osteoporotic vertebral compression fractures and degenerative spinal deformity. The impact of spinal disorders on health-related quality of life is more severe than the impact of many common diseases, such as cardiovascular diseases or type 2 diabetes. Spinal disorders affect more than 1.7 billion people worldwide and represent significant economic costs to society by the utilization of vast amounts of healthcare resources and by indirect costs such as loss of productivity. With the aging of our population the burden of spinal disorders on society is estimated to increase even further. Spinal aging encompasses a set of spinal disorders which are complex and heterogeneous with highly individualized surgical planning. As this patient category is associated with multiple medical comorbidities, decreased mobility, poor balance, and a greater propensity to falling, more patient tailored and multidisciplinary treatment strategies will be needed. Due to the confluence of an aging population and an increased capacity and willingness by the spinal community to manage difficult problems in older patients, it is essential that, when designing and implementing therapeutic strategies, clinicians must consider all of these factors. By shared decision making, medical and technical knowledge from surgeons is combined with values and preferences from patients in order to achieve effective and safe treatment modalities and ensure adequate patient support. This thesis addresses both clinical and preclinical aspects of spinal aging. In anticipation of an aging population, the main motivation of this thesis was to emphasize the significant and growing burden of spinal disorders in the elderly; to optimize current conservative and operative treatment for spinal aging; and to argue that allocation of resources to the management of spinal disorders should be a priority for our healthcare economy

Mechanics of Biomaterials

The mechanical behavior of biomedical materials and biological tissues are important for their proper function. This holds true, not only for biomaterials and tissues whose main function is structural such as skeletal tissues and their synthetic substitutes, but also for other tissues and biomaterials. Moreover, there is an intimate relationship between mechanics and biology at different spatial and temporal scales. It is therefore important to study the mechanical behavior of both synthetic and livingbiomaterials. This Special Issue aims to serve as a forum for communicating the latest findings and trends in the study of the mechanical behavior of biomedical materials

Book of Abstracts 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization

In this edition, the two events will run together as a single conference, highlighting the strong connection with the Taylor & Francis journals: Computer Methods in Biomechanics and Biomedical Engineering (John Middleton and Christopher Jacobs, Eds.) and Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization (JoãoManuel R.S. Tavares, Ed.). The conference has become a major international meeting on computational biomechanics, imaging andvisualization. In this edition, the main program includes 212 presentations. In addition, sixteen renowned researchers will give plenary keynotes, addressing current challenges in computational biomechanics and biomedical imaging. In Lisbon, for the first time, a session dedicated to award the winner of the Best Paper in CMBBE Journal will take place. We believe that CMBBE2018 will have a strong impact on the development of computational biomechanics and biomedical imaging and visualization, identifying emerging areas of research and promoting the collaboration and networking between participants. This impact is evidenced through the well-known research groups, commercial companies and scientific organizations, who continue to support and sponsor the CMBBE meeting series. In fact, the conference is enriched with five workshops on specific scientific topics and commercial software.info:eu-repo/semantics/draf