Planning the Surgical Correction of Spinal Deformities: Toward the Identification of the Biomechanical Principles by Means of Numerical Simulation

The set of surgical devices and techniques to perform spine deformity correction has widened dramatically. Nevertheless, the rate of complications due to mechanical failure remains rather high. Indeed, basic research about the principles of deformity correction and the optimal surgical strategies (i.e. the choice of the fusion length, the most appropriate instrumentation, the degree of tolerable correction) did not progress as much as the techniques. In this work, a software approach for the biomechanical simulation of the correction of patient-specific spinal deformities aimed to the identification of its biomechanical principles is presented. The method is based on three dimensional reconstructions of the spinal anatomy obtained from biplanar radiographic images. A user-friendly graphical interface allows for the planning of the deformity correction and to simulate the instrumentation. Robust meshing of the instrumented spine is provided by using consolidated computational geometry and meshing libraries. Based on finite element simulation, the program predicts the loads acting in the instrumentation as well as in the biological tissues. A simple test case (reduction of a low grade spondylolisthesis at L3-L4) was simulated as a proof-of-concept. Despite the limitations of this approach, the preliminary outcome is promising and encourages a wide effort towards its refinement

A novel finite element model of the ovine lumbar intervertebral disc with anisotropic hyperelastic material properties

The Ovine spine is an accepted model to investigate the biomechanical behaviour of the human lumbar one. Indeed, the use of animal models for in vitro studies is necessary to investigate the mechanical behaviour of biological tissue, but needs to be reduced for ethical and social reasons. The aim of this study was to create a finite element model of the lumbar intervertebral disc of the sheep that may help to refine the understanding of parallel in vitro experiments and that can be used to predict when mechanical failure occurs. Anisotropic hyperelastic material properties were assigned to the annulus fibrosus and factorial optimization analyses were performed to find out the optimal parameters of the ground substance and of the collagen fibers. For the ground substance of the annulus fibrosus the investigation was based on experimental data taken from the literature, while for the collagen fibers tensile tests on annulus specimens were conducted. Flexibility analysis in flexion-extension, lateral bending and axial rotation were conducted. Different material properties for the anterior, lateral and posterior regions of the annulus were found. The posterior part resulted the stiffest region in compression whereas the anterior one the stiffest region in tension. Since the flexibility outcomes were in a good agreement with the literature data, we considered this model suitable to be used in conjunction with in vitro and in vivo tests to investigate the mechanical behaviour of the ovine lumbar disc

Time-bin entangled photon pairs from Bragg-reflection waveguides

This work was supported by the Austrian Science Fund (FWF) through the project nos. I 2065 and J 4125, the DFG project no. SCHN1376/2-1, the ERC project EnSeNa (257531), the State of Bavaria and China Scholarship Council (201503170272).Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state’s density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of 88.9(1.8)% and a fidelity of 94.2(9)% with respect to a Bell state.Publisher PDFPeer reviewe

Roofing Arena Wien : Überdachung der Arena Wien in Leichtbauweise

Zsfassung in engl. SpracheGegenstand dieser Arbeit ist ein Entwurf für die Überdachung und Neugestaltung des Open-Air-Bereiches der Arena Wien. Die Möglichkeit den Open-Air-Bereich der Arena auch bei Schlechtwetter nützen zu können ist für den Verein eine willkommene Chance die Festivalzeit früher im Jahr zu beginnen und später zu beenden. Schlecht ablaufendes Regenwasser am tiefsten Punkt des Zuschauerraumes macht ein Betreten bei Regen unmöglich und mindert somit das Vergnügen an Konzerten und Veranstaltungen. Das Ziel dieser Arbeit ist daher einen Entwurf für eine Überdachung zu entwickeln, der die schützenswerten Backsteinbauten respektiert, jedoch seine schützende Hand über die von der Zeit stark in Mitleidenschaft gezogene Bausubstanz legt. Die Neugestaltung des Freiraumes soll harmonisch mit dem Dach in Einklang stehen, neue Perspektiven ermögliche und die aktuellen Problemstellen beheben. Anhand von Arbeitsmodellen in unterschiedlichen Maßstäben wurden die technischen Möglichkeiten ausgelotet und die Formfindung vorangetrieben. Funktionsmodelle von einzelnen Tragwerksteilen wurden angefertigt um sie später im Gesamtsystem anzuwenden oder auf ihre Gebrauchstauglichkeit in diesem speziellen Fall zu untersuchen. Das Ergebnis ist eine Dachkonstruktion, die Dank zweierlei Konstruktionsmethoden die Möglichkeit bietet mit geringem Materialaufwand große Spannweiten zu überbrücken und gleichzeitig einzudecken. Des weiteren wurde eine funktionelle Freiraumgestaltung geschaffen, die die Ansprüche des Schauplatzes vollends erfüllt und mit dem Dach gemeinsam ein stimmiges Bild erzeugt.The object of this thesis is to develop a canopy for the open-air location of the Arena Wien and to recreate the landscape of its court. The possibility to use the open-air-area of the Arena Wien even under bad weather conditions would be a great chance for the club to extend the periode of openair festivals from spring to autumn. At the lowest point of the audience-area there is no possibility for rain water to drain sothat guest can not use that erea. This makes it hard to enjoy concerts and events. The aim of this thesis is to develop a canopy that respects the old brick walls and does not touch consisting buildings, but at the same time helps the conserve the historic buildings. The renewing of the landscape inside the court must cooperate with the canopy, open new views and must remove all the consisting failures. The technical posibilities were fathomed by building working models in differnt sizes that also helped to find the form. Functunal models of single parts of the carrying stucture where built to proove them later in the whole model and to find out if they where useful in that speciffic case. The result is a canopy that offers the possibility to span wide expanses with very low amount of material and cover wide areas at the same time. Further a functional landscape was built that fulfills all the demands of an open-air-area and creates a harmonic picture in combination with the roof.12

Computational investigation on the aetiology of adolescent idiopathic scoliosis

The aetiology of scoliosis during adolescence is in most cases (85%) unknown (idiopathic). To investigate potential causes and treatments of scoliosis, a fully parametric finite element model of the spine and chest was developed. This work investigated the principle hypothesis that adolescent idiopathic scoliosis (AIS) is triggered by an asymmetrical load distribution resulting in a malformation of the bone. Furthermore, the impact of a potential asymmetry in the intrapleural pressure (IPP) distribution on the spinal shape was explored. The biomechanical aspect of the hypothesis was analysed using a subject-specific numerical model of the human spine (levels: T1-S1) and rib cage of a healthy 13-year-old male. The finite element model was generated using a self-developed program which allows a rapid semi-automatic generation of numerical models that consider the patient-specific morphology and a predefined flexibility of the main joints. The material properties of the soft-tissue were primarily extracted from literature. The material properties of the spinal segments and costovertebral joints were further optimized to fit the specific range of motion obtained from in vitro tests. In view of the close relationship between the form and function of the skeleton, the bone morphology of the spine and chest was quantified using CT data of individuals. The comparison of the bone morphology of patients, with (n = 21, 15 ± 2 years) and without (n = 48, 23 ± 12 years) AIS, revealed a characteristic morphological pattern in patients with AIS. This pattern included wedging and rotation of the vertebral bodies, differences between the right and left pedicle and facet size, as well as, asymmetrical rib cage deformities. This indicates the presence of an inherent asymmetrical stress distribution along the scoliotic spine. It should be noted, however, that in the non-scoliotic patient group a predisposition towards a characteristic scoliotic curvature was on average also observed. Simulations of various assumed intrapleural pressure distributions suggest that an asymmetrical intrapleural pressure can lead to spinal deformation patterns comparable to those seen in scoliotic spines. In particular, the pressure within the dorsal section of the rib cage had a strong influence on vertebral rotation, whereas the pressure in medial and ventral regions demonstrated a lateral displacement. An asymmetrical pressure between the left and right hemithorax resulted in lateral deviation of the spine towards the side of the reduced magnitude of negative pressure. The application of the IPP, assumed within the numerical model, resulted in a compressive force of 22.3 N in craniocaudal direction of the spine, which corresponds to 2.3 kg of organ weight. This reaction force supports the assumption that the IPP contributes in counterbalancing the weight of the intrathoracic organs. Due to the current lack of a non-invasive method to measure the IPP in vivo, clinical verification of the influence of the IPP on spinal stability remains unclear and challenging. It is known, however, that scoliosis can develop secondarily to surgical interventions of the pleura. In conclusion, the results of this study suggest that the intrapleural pressure distribution has the potential to play a key role in the development of spinal deformities. The interaction between the pleural physiology and the thorax may be an important piece in the puzzle to further understand the biomechanical in vivo condition and explain various spinal pathologies. Furthermore, the developed numerical model is suitable to simulate the biomechanics of the spine and chest. It can be a useful tool to investigate various spinal pathologies and treatment strategies

Endovenous thermal ablation of superficial truncal veins and compression therapy result in symptom relief in venous valve aplasia

Venous valve aplasia (or valvular rarefication) is a rare cause of chronic venous insufficiency. In the present report, we have described the case of a 33-year-old man with severe symmetric lower leg edema and heaviness and pain in both lower legs. Duplex ultrasound demonstrated severe venous insufficiency in the superficial and deep venous system of both legs. Further imaging examinations supported the diagnosis of venous valvular aplasia. Treatment consisted of endovenous thermal ablation of the great saphenous vein and small saphenous vein as well as consistent compression therapy, resulting in a marked reduction of his leg edema, heaviness, and pain

The Role of the Size and Location of the Tumors and of the Vertebral Anatomy in Determining the Structural Stability of the Metastatically Involved Spine: a Finite Element Study

Vertebral fractures associated with the loss of structural integrity of neoplastic vertebrae are common, and determined to the deterioration of the bone quality in the lesion area. The prediction of the fracture risk in metastatically involved spines can guide in deciding if preventive solutions, such as medical prophylaxis, bracing, or surgery are indicated for the patient. In this study, finite element models of 22 thoracolumbar vertebrae were built based on CT scans of three spines, covering a wide spectrum of possible clinical scenarios in terms of age, bone quality and degenerative features, taking into account the local material properties of bone tissue. Simulations were performed in order to investigate the effect of the size and location of the tumoral lesion, the bone quality and the vertebral level in determining the structural stability of the neoplastic vertebrae. Tumors with random size and positions were added to the models, for a total of 660 simulations in which a compressive load was simulated. Results highlighted the fundamental role of the tumor size, whereas the other parameters had a lower, but non-negligible impact on the axial collapse of the vertebra, the vertebral bulge in the transverse plane and the canal narrowing under the application of the load. All the considered parameters are radiologically measurable, and can therefore be translated in a straightforward way to the clinical practice to support decisions about preventive treatment of metastatic fractures

The use of computational models in orthopedic biomechanical research

In recent years, the importance of computational modeling for the investigation of research questions in the field of orthopedics has been continuously increasing. The available literature currently contains thousands of papers and covers all the major joints and anatomical regions. This chapter describes some of the most relevant papers in which computational models, either based on multibody mechanics or finite element analysis, were used to investigate clinical issues in the orthopedics field, covering published studies about hip, knee, ankle, and shoulder joints, as well as the spine. For each of these anatomical regions, relevant studies investigating it in native conditions, either healthy or showing degenerative features, as well as after the most common surgical procedures aimed at treating degenerative disorders, are briefly summarized. Validation and limitations of the available models as well as foreseeable future developments are described as well. The literature analysis highlighted some emerging trends such as patient-specific modeling and multi-scale approaches, which would increase the impact of numerical analysis in orthopedics by implementing the so-called personalized medicine, with direct consequences on treatment options and clinical outcomes for specific patients. On the other side, the limited access to patient-specific and degeneration-specific material properties, as well as the difficulties in calibrating and validating personalized models, limits the spread and the validity of such models.SCOPUS: ch.binfo:eu-repo/semantics/publishe

Simultaneous Measurements of Unsteady Aerodynamic Loads, Flow Velocity Fields, Position and Wing Deformations of MAVs in Plunging Motion

A new wind tunnel environment for low Reynolds number testing of Micro Air Vehicles (MAV) is introduced, providing a test rig for plunge and pitch motions as well as an especially designed 6-component balance to obtain dynamic force data. In this study a rigid as well as a flexible version of a typical MAV wing is investi-gated with respect to flexibility effects. Optical measurements techniques are adapted to measure simultaneously the instantaneous model position, orientation, wing deformations and flow fields

Comparison between finite element simulations and experimental tests of the uniaxial tension response of the annulus fibrosus.

<p>Experimental and numerical stress—strain curves of the (a) anterior, (b) lateral and (c) posterior specimens. Anterior, Lateral and Posterior represent the experimental results; FE Anterior, FE Lateral and FE Posterior represent the numerical results; Poly. is the quadratic polynomial interpolation of the experimental results. The experimental curves represent the median values of the stresses. For each measured value, the first and the third quartile are reported. Median values were used to calculate stress-strain response because of the non-normality of the distribution.</p