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Sex differences in vertebral bone characteristic, loading patterns and the factor of risk in prepubertal childrenFuller, Arwen A. 09 March 2004 (has links)
Sex differences in bone mass and size are thought to contribute to the greater
incidence of vertebral fractures in women. While these sex differences are widely
recognized, the relative contributions of bone mass, bone density, and bone size to the
differences in vertebral strength and fracture risk between men and women have not
been fully delineated. Furthermore, it is unknown whether the roles of each of these
factors in determining vertebral strength change differently with age in men and
women. We studied the bone content, density and geometry as well as vertebral
loading and the factor of risk of the L3 vertebra in a sample of prepubertal males and
females. Our first aim was to assess differences in vertebral bone dimensions, bone
density, vertebral loading patterns and fracture risk, as measured by the factor of risk,
in prepubertal children. Our second aim was to determine whether pre-pubertal
growth affects the geometry and density of L3 differently in boys and girls. We
measured vertebral dimensions, cross-sectional area and volumetric BMD of the third
lumbar vertebral body in 93 prepubertal children (54 boys and 39 girls), using dual-energy
X-ray absorptiometry scans obtained in the posterior-anterior and lateral
projections. We also employed basic biomechanics to estimate vertebral loading
during upright standing and forward bending. Bone strength and loading data were
used to assess sex differences in the factor of risk in prepubertal children. Twenty
children (11 boys and 9 girls) were assessed at baseline and seven months later to
examine the effects of growth on bone size and vBMD. At baseline, boys and girls
were similar for age, height, weight and calcium intake. L3 width and depth were
6.7% and 5.8% greater in boys than girls, respectively (P<0.001 and P=0.01,
respectively). In contrast, vertebral height was 3.5% greater in girls than boys (P=
0.04). While vertebral loading was similar between sexes, stresses on the spine were
12.2% lower in boys during upright standing and 12.0% lower in boys during forward
bending at both 50° and 90°, as compared to girls (P<0.001, P<0.01 and P<0.01,
respectively). The factor of risk was similar between boys and girls under each
loading condition. During growth, changes in vertebral size and density were not
different between boys and girls. Our results indicate that even prior to puberty, sex
differences in vertebral size contribute to differences in vertebral stress during
standing and forward bending. Furthermore, before the onset of puberty, growth does
not result in disparate changes between sexes. / Graduation date: 2004
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Kinematic assessment of lumbar segmental instability using digital fluoroscopic videoTeyhen, Deydre Smyth 28 August 2008 (has links)
Not available / text
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An experimental and numerical evaluation of an interbody spinal fusion deviceRossouw, M.M. 25 November 2013 (has links)
M.Ing. (Mechanical Engineering) / A stand-alone anterior lumbar interbody fusion device is used to stabilise the spine and restore the disc space height without any other instrumentation. The stand-alone anterior lumbar interbody device is fixed to the adjacent vertebrae using titanium screws. In this research an experimental and numerical investigation on the structural strength of the SASCATM stand-alone anterior lumbar interbody fusion device are presented. The outcome of the investigation will be used as part of the device validation documentation necessary for market approval. The SASCATM device is manufactured from PEEK (a high strength polymer). Tensile and compressive testing was conducted to determine the appropriate mechanical properties of PEEK. The structural integrity of the SASCA device was evaluated by conducting full scale compression testing on a limited number of different design revisions. Comparisons as regards to their loaddisplacement behaviour were made. All specimens were visually inspected. The Finite Element Analysis (FEA) method was used in the numerical investigation of the SASCATM stand-alone anterior lumbar interbody device. Three studies were conducted. The first study aimed at comparing the full scale experimental compressive testing results with the FEA simulation. Although the desired results weren’t achieved, the model gave a fair representation of the initial region of the experimental setup in the sense that it had a similar slope. It was concluded that the nominal stress (4.1 MPa) fell within the proportional limit (35 MPa) as measured during the materials testing. The second study was aimed at determining the displacement at a worst-case load determined from the literature (2.7 kN). The study showed that the maximum Von Mises stress does not exceed the yield strength of the material. The third and final (parametric) study aimed at geometric optimisation of the cages. The motivation for the changes was based on the literature and customer suggestions for improvement. The geometric optimisation intended to show whether a desired increase in graft hole size would have an effect on the structural integrity of the device. The suggestion to move the screw holes of the threehole version closer to the center of the cage was also assessed. It was shown that enlarging the two graft holes does have an effect on the compressive strength. Higher stresses were presented in all but one case. Combining the holes also had an effect on the compressive strength. Movement of the screw holes more medially did have an impact on the compressive strength of the cages. The effect was significant. The closer the holes were to the center of the cage, the higher the Von Mises stress was. This change should therefore be considered before implementation. The results showed that different shapes and sizes of the graft holes do have an impact on the stress of this particular cage. None of the models exceeded the compressive yield strength of the material. The proposed graft hole opening design changes are therefore not warranted for the current SASCATM stand-alone anterior lumbar interbody device.
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