EXPERIMENTAL MODEL OF HUMAN SPINE DURING LOADING

  • J. Castro Goncalves

Abstract

INTRODUCTION -This paper presents an experimental model of the human spine built up with real vertebrae The main objective of the work is to investigate the intensity and nature of the forces developed in the lower part of the human spine due to bending, extension and rotation. Electrical strain gauges were used to monitoring the strains developed in the vertebrae, for the types of loads that have been considered. METHODS -This kind of study has serious modelling problems in the building of the model, in order to get a general behaviour of the whole not completely deprived of characteristics One of the most serious problems is related to the functioning of the intervertebrae disks which, due to the drying of the hydrophil tissue, loose flexibility For the measurement of the disk elastic properties we had to substitute it for a material with a similar height. A contact glue, that proved to have a good adhesion was used to fix it to each one of the vertebrae The muscular strengths and ligaments acting on the back ant front areas were simulated using rubber strings with a diameter of 3 mm These strings were fastened to metal hooks we kept them tensioned using a tying device, as you can see In order to get a greater consistence, make possible a more efficient load transfer and increase as much as possible the ability to repeat the movements, the articulate facet were involved in silicon rubber. CONCLUSIONS -The analysis of the model behaviour shows that comparing a certain amount of Xrays taken in different positions of front bending, back extension and torsion, the model behaviour and its capacity of efficient simulation were proved. This comparison showed that the level of the simulation, is not the most perfect one; however it was possible to verified that the requests, when a back extension and torsion were imposed to the model, and which we thought ware very demanding, were quite minor when compared to the ones got by X-rays in a healthy person in a normal strain. Actually, the intervertebrae disks don't show the same flexibility, themselves. On the other hand the same material and the same height were used in the model to simulate the disks. This fact will allow in the future to improve the mechanical functioning of the model, choosing different materials for the disks simulations as weil for the rubbers of front and back simulation.