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A Thesis submitted to The University of Arizona College of Medicine - Phoenix in partial fulfillment of the requirements for the Degree of Doctor of Medicine. / A detailed pre‐operative examination of a child’s neurovascular status following pediatric elbow fractures is critical to the assessment of these injuries. Without proper documentation of the preoperative exam, apparent postoperative changes in the neurovascular examination may be difficult to determine, and may dictate different treatment strategies. The reported incidence of neurologic (11.3%) and vascular (0.3‐4.6%) injury associated with supracondylar fractures underscores the importance of the preoperative exam. The purpose of this prospective study was to determine how frequently a complete neurovascular exam could be completed in children with elbow fractures. A detailed, specific elbow fracture History and Physical form was developed for prospective use on all pediatric elbow fractures in a tertiary care pediatric trauma hospital from 2013 through 2014. Specific neurovascular exam criteria were documented in an easily used checklist form. Demographic data collected included age, BMI, mechanism of injury, fracture type, comorbidities, pre‐operative pain management, and the operative procedure performed. There were 163 patients meeting the inclusion criteria. Attempted neurovascular (NV) exam was documented in 146 of these patients (89.6%). A clinically reliable, complete NV exam was possible in 104 patients (71.2%). In the remainder of the children, the clinician could not determine at least one aspect of the neurovascular exam. A significant correlation was found between age of the subject and ability to obtain a complete exam, with younger children less than age 5 being more likely to have incomplete information on the NV exam (p<0.000001). Gender, BMI, fracture type, pre‐assessment pain control, and potential language barriers had no effect on whether or not the exam was complete. Although a complete and detailed neurovascular examination is considered necessary when evaluating pediatric elbow fractures, over a fourth of our patients (29%) were unable to reliably participate in a full preoperative neurovascular exam. Younger children (less than 5 years of age) were less likely to participate in a complete neurovascular assessment. Neurovascular examinations in the setting of elbow fractures in children less than five years of age were unreliable and incomplete.

Le tissu osseux et le tissu cutané partagent de nombreuses similitudes. En effet, ce sont tous les deux des tissus conjonctifs composés majoritairement de collagène de type 1. Ainsi, certains ont émis l’hypothèse que l’altération de leurs propriétés secondaire au vieillissement intrinsèque serait comparable. Il pourrait donc être intéressant de se baser sur cette hypothèse pour essayer d’estimer le vieillissement osseux à partir du vieillissement cutané. Pour tester cette hypothèse, nous avons considéré une situation particulièrement préoccupante chez les personnes âgées: les fractures controlatérales de l’extrémité proximale du fémur. Dans une première étude, nous avons montré que l’estimation du risque mécanique individuel de fracture controlatérale du col fémoral par la DMO n’était pas optimal. Sur une cohorte continue de 49 patients ayant eu une fracture ostéoporotique du col fémoral, nous avons démontré par une analyse inverse éléments finis que la DMO des têtes fémorales explantées n’étaient corrélée avec aucun paramètre mécanique macroscopique ou microscopique. Par contre, l’estimation de l’altération des tissus mous semble être corrélée au risque de fracture du col voire même encore plus précisément au risque de fracture du col fémoral controlatéral. Ainsi, nous avons montré dans une analyse séquentielle que les sujets ayant une fracture controlatérale du col fémoral avait un IMC plus faible et une altération de la peau du dos de la main plus importante que les sujets contrôle. Par contre, il semble que les méthodes étudiées pour un tissu ne permettent pas de déduire de façon fiable un autre paramètre osseux. A partir d’une revue systématique de la littérature, nous avons retrouvé que la plupart des caractéristiques de la peau étaient altérées avec le vieillissement intrinsèque et que ceci était corrélé dans une certaine mesure avec le degré d’ostéoporose. Cependant, ces corrélations étaient assez faibles et ne pourraient permettre de sélectionner les patients ostéoporotiques les plus à risque. C’est pourquoi nous avons décidé de tester un test cutané de surface reflétant les altérations mécaniques du tissu cutané avec l’âge et nous l’avons corrélé à des tests et mécaniques réalisés sur des têtes fémorales explantées pour fracture du col fémoral chez 37 patients consécutifs. Ceci nous a permis de montrer que l’altération des propriétés mécaniques cutanées était corrélée de façon statistiquement significative à une altération des propriétés mécaniques de l’extrémité proximale du fémur. Ainsi, nous proposons d’utiliser l’estimation du vieillissement cutané pour estimer le vieillissement osseux. De plus, nous montrons une corrélation entre une altération tissulaire authentifiée sur un test surfacique cutané et un risque mécanique intrinsèque plus élevé de fracture de l’extrémité proximale du fémur. / Bone and skin tissue share many similarities. Indeed, both are connective tissues and are mainly comprised of type 1 collagen. Thus, some have speculated that the alteration of their properties secondary to intrinsic aging would be comparable. Based on this hypothesis, it could be interesting to try to estimate the bone aging from the skin aging. To test this hypothesis, we considered a notable situation in the elderly: the contralateral fractures of the proximal femur. In a first study, we showed that the estimation of the mechanical risk of contra-lateral femoral neck fracture by BMD was not working. From a cohort of 49 patients with an osteoporotic hip fracture, we demonstrated by inverse finite element analysis that BMD of explanted femoral heads were correlated with no macroscopic mechanical or microscopic parameter. However, the estimation of the soft tissue alteration seems to be correlated to the risk of fracture of the neck and even more precisely to the contralateral femoral neck fracture. Thus, we showed in sequential study that subjects with contralateral femoral neck fracture had a lower BMI and a more impaired skin of the back of the hand than control subjects. However, it appears that every method used to study the skin tissue do not allow to deduce reliably every bone parameter. From a systematic review of the literature, we found that most of the skin parameters that have been tested were altered with intrinsic aging and this was correlated to some extent with the degree osteoporosis. However, these correlations were statistically weak and could not allow selecting the osteoporotic patients who were the most at risk of fracture. That is why we decided to test a surfacic skin test reflecting the mechanical alteration of the skin tissue with age. Then, we correlated it with morphological and mechanical tests performed on explanted femoral heads after a hip fracture in 37 consecutive patients. With that study, we were able to show that the alterations of the cutaneous mechanical properties were statistically correlated with the altered mechanical properties of the proximal femur. Thus, we propose to use an estimation of the skin aging to estimate the bone aging. Furthermore, we found a correlation between the alterations of the surface of the skin tested with a surfacic test and a higher intrinsic mechanical risk of fracture of the proximal part of the femur.

"Residual stresses are a common and often undesired result of material processing, introduced through non-linear deformation and/or phase transformation of material under mechanical or thermo-mechanical loading. These macro stresses alter mechanical properties and the intrinsic fatigue crack growth characteristics of the material. Residual stress artifacts can introduce inconsistencies and significant errors when the true material behavior is needed for material development and optimization and for structural component design. The effects of quenching residual stresses on fatigue crack propagation behavior of various materials were investigated. In parallel, residual stresses similar in magnitude and distribution with the quenching residual stresses were generated using mechanical processes to decouple the effects of residual stresses from microstructural effects. Mechanical residual stress distributions predicted by 3D elastic-plastic finite element analysis showed good agreement with the stresses measured on fatigue crack growth testing specimens using fracture mechanics approaches. Crack propagation characteristics in fields with low and high residual stresses were studied using optical and scanning electron microscopy, and the effects of residual stress on crack path behavior were assessed. An original residual stress analytical correction to fatigue crack growth data was developed, compared to existing corrective methodologies, and validated using residual stress free data. Overall, the work provides tools to understand, control, and correct the effects of processing residual stresses on fatigue crack growth for accurate fatigue critical design and life predictions."

Concrete is a highly non-homogeneous composite with large heterogeneities of quasi-brittle character. Failure of concrete structures is usually accompanied by cracking of concrete, which is strongly affected by the mesoscale structure and the behaviour of the interface between the aggregates and the mortar matrix, especially under complex stress conditions. Analysis of the failure mechanisms of concrete at the mesoscale is therefore crucial for a better understanding of the macroscopic behaviour of the material, which can in turn contribute to improved design of concrete structures and finding new ways to enhance the material properties. This research aims to investigate the intrinsic failure mechanisms of concrete-like materials from a mesoscale point of view. To do this, continued developments from existing work on mesoscale modelling are carried out to cater the needs of realistically simulating the damage process in concrete under complex loading conditions. The new developments focus on two key aspects. Firstly, techniques to realistically simulate the fracture process of concrete are developed and these involve the incorporation of a combined cohesive and contact mechanisms for the interface between aggregates and mortar matrix. Such interface modelling allows the crack initiation and propagation at the mesoscale to be explicitly represented. Secondly, a full 3D mesoscale finite element model for concrete-like materials with random aggregates and the possibility of high packing density is developed. Use is then made of these enhanced mesoscale models to explore the intrinsic mechanism governing the fundamental behaviour of concrete such as fracture propagation in tension and compression, the well-known size effect and the dynamic strain rate effect. The research investigation begins with an analysis of the size effect in plain concrete beams under three-point bending using a generic 2D mesoscale model. The analysis aims to provide preliminary insight into the use of a mesoscopic computational tool for examining the concrete damage mechanisms with the well-known size effect phenomenon as a benchmark scenario. The shapes and the sizes of the fracture process zone (FPZ) during the whole fracture process are captured. The role of detailed FPZ features is discussed accordingly. On the other hand, the results also point out the deficiencies of the continuum-based mesoscale framework at capturing the evolution of the local fracture process, and to resolve this problem requires explicit simulation of the initiation and propagation of the micro-cracks and thus a realistic reproduction of the fracture process zone, and this becomes the subject of research in much of the later chapters of the thesis. To cater to the needs of better representing the fracture process in concrete, a coupled cohesive-contact interface approach is proposed to model the crack initiation, crack propagation and the friction mechanism within the transition zone between the coarse aggregates and the mortar matrix. The cohesive-contact combined model is verified to perform well under simple as well as complex loading conditions. The interface approach in a mesoscale model framework provides a new platform for investigating the failure mechanisms in terms of the cohesive fracture process and the contact friction process. A more comprehensive and robust mesoscale interface modelling approach, in which the cohesive plus contact interface is inserted along all mesh grids, is developed to study the complex dynamic behaviour of concrete with the consideration that fractures can spread in a fine distributed manner within larger damage areas including the strong aggregate, particularly under high loading rate. By allowing local fractures to develop explicitly, the issues with fracture damage description with a continuum material model can be largely resolved. The effectiveness of such an approach is demonstrated and employed in an investigation into the intrinsic mechanisms governing the sensitivity of the dynamic tension resistance with the loading rate. Subsequently, a re-visit of the size effect in terms of the evolution of the fracture process zones using the mesoscale model with cohesive plus contact interface model is conducted and the results are presented. The preliminary observations from using the continuum-based mesoscale model are examined and verified. Additional insight into the fracture processes in the concrete beams with various sizes is obtained and the intrinsic mechanisms of the size effect are further discussed. On the real 3D mesoscale modelling methodology, the new development focuses on achieving a realistic representation of the actual shapes and sizes of aggregate particles and at the same time allowing for high volumetric ratios of aggregates (packing density) to be attained. In addition to specific techniques to enhance the conventional take-and-place procedure, an algorithm to generate supplementary aggregates to allow increased packing density is proposed and implemented. Example 3D mesoscale specimens so created are then verified against standard experimental tests such as uniaxial compression, uniaxial tension and compression with lateral confinements, and applied to examine the dynamic behaviour of concrete under high strain rate compression.

Thesis (Ph. D.)--University of Washington, 1983. / Vita. Includes bibliographical references.