Biomecânica da articulação interfalângica proximal-nativa versus artroplástica

Mestrado em Engenharia MecânicaA presente dissertação teve como principal objetivo o estudo de aspetos biomecânicos da articulação interfalângica proximal da mão, mais precisamente as alterações induzidas pela artroplastia, quando comparado com a articulação no estado nativo. Numa primeira etapa realizou-se uma análise detalhada dos aspetos anatómicos, biomecânicos, patológicos e respetivos tratamentos da articulação com especial enfoque no processo artroplástico desta. Posteriormente, desenvolveram-se os modelos geométricos das estruturas ósseas envolvidas e respetivos implantes com base na digitalização destas estruturas físicas. Na fase posterior desenvolveram-se os modelos numéricos de elementos finitos da condição da articulação nativa e protésica. Os modelos representativos da condição protésica simularam duas situações de interface entre o implante e o osso, por forma a representar duas condições cirúrgicas distintivas, uma representativa de um estado pós cirúrgico e a outra de um estado de médio-longo termo, onde é suposto uma boa ancoragem do implante ao osso. Nestes modelos foram analisados e comparados os estados de deformação no osso, estabilidade do implante e os níveis de tensão no implante para as diferentes condições de carga. De seguida, desenvolveram-se modelos experimentais da articulação com recursos a modelos ósseos especificamente desenvolvidos para o efeito, constituídos por um corpo interior em espuma, replicando a estrutura de osso esponjoso, e uma casca externa em resina epóxi reforçada com fibra de vidro, replicando a estrutura de osso cortical. Estes modelos foram instrumentados com extensómetros nas suas superfícies por forma a avaliar os estados de deformação na sua condição nativa e artroplástica para duas condições de carga distintas representativas de atividades diárias da mão, avaliando-se assim a alterações de transferência de carga no córtex. Os resultados dos modelos numéricos foram comparados com os experimentais, obtendo-se uma boa correlação entre estes. As deformações nas falanges quer nos modelos numéricos, quer experimentais, demonstram uma clara alteração na transferência de carga entre o modelo nativo e o artroplástico. Observou-se um aumento das deformações no osso esponjoso na condição pós-cirúrgica, alterações que estão diretamente relacionadas ao risco de falência do osso por sobrecarga localizada associada a um efeito de fadiga por ação de cargas cíclicas. Na condição de médio-longo termo, o risco identificado está associado a uma redução das deformações nas regiões ósseas vizinhas do implante, relativamente à condição nativa, e pode associar-se este efeito de stressshielding a um potencial risco de reabsorção óssea a termo. Conclui-se assim que a artroplastia da articulação interfalângica proximal altera de forma relevante o comportamento biomecânico das falanges, aportando riscos de origens distintas que eventualmente podem ser minorados por um otimização da geometria e materiais do implante e limitação da condições de carga a impor à articulação num estado pós-cirúrgico.The main objective of this work was the study of biomechanical aspects of the proximal interphalangeal joint of the hand, specifically the changes induced by arthroplasty, when compared with the joint in the native state. The first step was the accomplishment of a detailed a detailed analysis of the anatomical aspects, biochemical, pathological and respective treatments of the joint with special focus on artroplastic process. After, iwere developed the geometric models of the bone structures involved and their respective implants based on the scanning of these physical structures. Posteriorly, were developed the numerical finite element models of the condition of native and prosthetic joint. Representative models of the prosthetic condition simulate two interface conditions between the implant and the bone in order to represent two distinctive surgical conditions, one refers to a post-surgical state and the other refers to a state of medium to long term, in which is supposed a good anchorage of the implant to the bone. In these models were analyzed and compared deformation states of the bone, the implant stability and the implant voltage levels for different load conditions. Then, were developed experimental models of the joint, through the resource of bone models developed specifically for this purpose, constituted by an inner foam body, replicating the cancellous bone structure, and an outer shell epoxy resin reinforced with fiberglass, replicating cortical bone structure. These models were instrumented with strain gauge on their surfaces, in order to evaluate the deformation states in its native condition and in its arthroplasty condition for two different load conditions that represents daily activities using the hand, evaluating thus the charge transfer changes in the cortex.. The results of numerical models were compared with the experimentals, yielding a good correlation between them. The deformation of the phalanges in the numerical models and in the experimental models, shows a clear change in charge transfer between the native and the artroplastic. There was an increase of deformations in the cancellous bone in post-surgical condition, these changes are directly related to the risk of failure of bone through a located overhead associated with a fatigue effect of the cyclic loading action. In the condition of medium-long term, the identified risk is associated with a reduction of the deformations in the surrounding bone regions of the implant relative to the native condition, and this stress-shielding effect can be associated with the potential risk of bone resorption term. It is therefore concluded that the arthroplasty proximal interphalangeal joint changes the biomechanical behavior of the phalanges, bringing risks of different origins that can possibly be alleviated by optimizing the geometry and implant materials and limiting loading conditions to the joint in a postsurgical state

Stochastic Urban Pluvial Flood Hazard Maps Based upon a Spatial-Temporal Rainfall Generator

It is a common practice to assign the return period of a given storm event to the urban pluvial flood event that such storm generates. However, this approach may be inappropriate as rainfall events with the same return period can produce different urban pluvial flooding events, i.e., with different associated flood extent, water levels and return periods. This depends on the characteristics of the rainfall events, such as spatial variability, and on other characteristics of the sewer system and the catchment. To address this, the paper presents an innovative contribution to produce stochastic urban pluvial flood hazard maps. A stochastic rainfall generator for urban-scale applications was employed to generate an ensemble of spatially—and temporally—variable design storms with similar return period. These were used as input to the urban drainage model of a pilot urban catchment (~9 km2) located in London, UK. Stochastic flood hazard maps were generated through a frequency analysis of the flooding generated by the various storm events. The stochastic flood hazard maps obtained show that rainfall spatial-temporal variability is an important factor in the estimation of flood likelihood in urban areas. Moreover, as compared to the flood hazard maps obtained by using a single spatially-uniform storm event, the stochastic maps generated in this study provide a more comprehensive assessment of flood hazard which enables better informed flood risk management decisions.status: publishe

Hydraulic and water quality modelling of urban drainage systems

As inundações urbanas estão se tornando cada vez mais frequentes, de tal forma que a União Europeia publicou a Diretiva 2007/60/CE no sentido de mitigar as consequências relacionadas com este fenômeno e de impor limites à concentração de poluentes nas águas pluviais. O objetivo deste artigo foi apresentar uma modelação dos sistemas de drenagem em situação de inundações, baseada no software da United States Environmental Protection Agency (EPA), Storm Water Management Model (SWMM), em que o estudo de caso é analisar um sistema de drenagem urbana unitário, inserido na Zona Central de Coimbra, em Portugal. Recorrendo à metodologia Automatic Overland Flow Delineation (AOFD) para a geração de uma rede de drenagem superficial e implementando-a no SWMM, obteve-se um modelo de drenagem dual, que permite a análise do escoamento em situação de inundações, incluindo o controle de escoamento entre a superfície e a rede de coletores e a modelação da qualidade da água à superfície. Este modelo permite quantificar a carga poluente à superfície, relativamente ao parâmetro de sólidos suspensos totais, para um evento de precipitação extrema.Urban floods are becoming more frequent. Thus, the European Union published the Directive 2007/60/CE to mitigate costs related with this phenomenon and to impose limits on the concentration of pollutants in pluvial water. The purpose of this study was to present the modelling of drainage systems in flood situations, based on the software of the United States Environmental Protection Agency (EPA), the Storm Water Management Model (SWMM), in which the study case is to analyze a unitary urban drainage system of Zona Central catchment in Coimbra, Portugal. By using the Automatic Overland Flow Delineation (AOFD) methodology for the generation of a superficial drainage network and implementing it in the SWMM, it was obtained a dual drainage model that allows the flow analysis in flood conditions, including flow control between the surface and collectors network and also modeling of water quality at the surface. This model allows quantifying the pollution load at the surface, relatively to the parameter of total suspended solids, for any extreme rainfall event

Delaying surgery for patients with a previous SARS-CoV-2 infection

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The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AimThe SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery.MethodsThis was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin.ResultsOverall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P ConclusionOne in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease