ABSTRACT
A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.
Subject(s)
Imaging, Three-Dimensional/methods , Models, Biological , Scapula/diagnostic imaging , Scapula/physiology , Weight-Bearing/physiology , Aged , Aged, 80 and over , Cadaver , Compressive Strength , Computer Simulation , Elasticity , Female , Finite Element Analysis , Humans , In Vitro Techniques , Radiography , Reproducibility of Results , Sensitivity and Specificity , Stress, MechanicalABSTRACT
In the present report we describe the construction of a systemic vascular perfusion device designed to perfuse small mammals with fixatives under a constant, controlled hydrostatic pressure. The device is powered by compressed-air. The construction of the device allows the interchange of vessels containing various perfusates during the perfusion, without having to interrupt the flow or alter the hydrostatic pressure. Large volumes of fixatives can be perfused in a relatively short time, leading to good preservation of brain tissue, both for light and electron microscopical purposes.
