STATISTICAL ASSIGNMENT

Biomechanics Practical Assignment



Biomechanics Practical Assignment

Introduction

Intervertebral discs in our spines exhibit biphasic behavior, where it is believed that the behavior of poroelastic (fluid) is dominated by the slower frequency loading, compared with faster loading, where the self-viscoelastic behavior of solid collagen-proteoglycan matrix is important. In addition, the liquid contents of the disc, it was shown that the change of its mechanical behavior.

The purpose of this study is to compare the effect of fluid content and frequency of loading on the stiffness of sheep intervertebral discs in axial compression. Criteria for assessing the rigidity of the linear plot of loading and hysteresis loss ratio should be calculated for each drive and test. Drive stiffness provides a measure of elastic response disk, and hysteresis loss ratio - a measure of energy absorption (damping) of the disk.

The aim of the experiments was to determine the direction of the convex ring under load, when intact, and when denucleated. This can be deduced from the movement of Alcian blue markers, as determined from their positions in the video images in the two extremes of loading: before compression and after compression.

The images were obtained from the video tape of each experiment using a frame capture hardware. For each compression test, the two images were obtained at one point, when the testing machine cross-head is just touching the specimen, and one at full compression. However, although the device was designed to preserve the core inside the disk, it was evident that the core extruded between the disc and Perspex window in nine of the intact specimens and three denucleated samples. For these samples, the images were made in the initial contact point, and then just before the extrusion is perceived to occur. As a result, images have shown samples that have not all experienced the same degree of compression.

Image analysis program was specially written for the measurement of markers in the images . This program has allowed the position of the markers in the horizontal direction (perpendicular to the direction of applied bias) should be measured. Position was measured relative to a fixed point on the tower, and each image is scaled to take into account differences in magnification. Each measurement was repeated five times, and the mean and standard error of the mean were calculated to give a more accurate assessment of the situation and an indication of errors. Position of the markers was then used to calculate the motion of each marker in compression. Error on the movement of value was also calculated using the formula for standard error propagation .

Movement of markers was then used to determine the direction moved by the disk tissue at this point. Direction, rather than quantity was used as described above, the images were analyzed in a variety of compression and, in addition, various discs may react differently due to their natural variability.

Three categories were defined to describe the motion of the marker: 'P'''or 'X'. Category "P" denotes that the direction of motion toward the back of the ...