Reverse engineering applied to a lumbar vertebra

Bone studies can be made in vivo or in vitro. However, disadvantages of both traditional techniques call for a compromise between the two. Reverse engineering allows in vitro bone samples to be simulated and analysed in a virtual in vivo environment thus offering a middle ground solution and a sound foundation on which biomechanical studies of bone could develop.peer-reviewe

Analysis of stress-strain distribution within a spinal segment

The biomechanical feedback of biological tissue is difficult to measure. A spinal segment model can be used to obtain fundamental information by means of a computer simulation using finite element analysis. The goal of this work is to study the biomechanical behavior of a spinal segment under varying conditions related to the deterioration of the material properties of the IVD. Decisions about the methodology of this research and get satisfactory answers had to be made in the very early stages of the project. Since it is very difficult, if not impossible, to obtain the complete complex data about the response of different components of the system by means of measurements in vivo, and in the view that measurements in vitro are not feasible due to the lack of available spinal segments as well as economic and time constraints, the situation called for the development of a reliable computational model. Such a model would allow the investigation of biomechanical deficiencies within a geometrically identical pathological spinal segment and assist the proper understanding of the role played by each anatomical structure of the system.peer-reviewe

Placement of trans-sternal wires according to an ellipsoid pressure vessel model of sternal forces

Funding from the University of Malta Medical School (Grant IMF/014/11) and University of Malta Research Fund (Grant 31/389/10) is gratefully acknowledged.Dehiscence of median sternotomy wounds remains a clinical problem. Wall forces in thin-walled pressure vessels can be calculated by membrane stress theory. An ellipsoid pressure vessel model of sternal forces is presented together with its application for optimal wire placement in the sternum. Sternal forces were calculated by computational simulation using an ellipsoid chest wall model. Sternal forces were correlated with different sternal thicknesses and radio-density as measured by computerized tomography (CT) scans of the sternum. A comparison of alternative placement of trans-sternal wires located either at the levels of the costal cartilages or the intercostal spaces was made. The ellipsoid pressure vessel model shows that higher levels of stress are operative at increasing chest diameter (P < 0.001). CT scans show that the thickness of the sternal body is on average 3 mm and 30% thicker (P < 0.001) and 53% more radio-dense (P < 0.001) at the costal cartilage levels when compared with adjacent intercostal spaces. This results in a decrease of average sternal stress from 438 kPa at the intercostal space level to 338 kPa at the costal cartilage level (P = 0.003). Biomechanical modelling suggests that placement of trans-sternal wires at the thicker bone and more radio-dense level of the costal cartilages will result in reduced stress.peer-reviewe

Can the foam model simulate the bone behaviour?

Dehiscence of median sternotomy wounds due to excessive forces caused by high pressure within the chest during coughing can lead to breaking closures sternotomy. This remains a clinical problem leading to significant risks of mortality and morbidity. The evaluation of the suture and the sternotomy biomechanical feedback is tested usually on the human cadaveric sternum or in some cases using suitable animal sternum. The foam sternal model was proposed as the alternative source that provides cheap, easily accessible sternum, without mentioning other advantages. The computational approach combined with experiment can provide more information about the foam behaviour and confirm the statement: “the foam model sternum behaves as a real bone” as advertised by supplier. The foam model sternum was scanned, and digitized geometry data was used to create the virtual computational model used to simulate the laboratory experiment by means of Finite Element Method. The data collected from the two experiments, the laboratory test and computational simulation, are compared and verified against the outcome of the experiment with the sternum from cadaver.peer-reviewe