Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

No description available.

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Thesis (MAppSc in Physiotherapy) -- University of South Australia

Made available in DSpace on 2014-06-11T19:34:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-22Bitstream added on 2014-06-13T21:06:51Z : No. of bitstreams: 1 lemos_ff_dr_guara_parcial.pdf: 67760 bytes, checksum: 8abbb6c32f12d888cf49226d69fd138e (MD5) Bitstreams deleted on 2014-10-03T16:24:39Z: lemos_ff_dr_guara_parcial.pdf,Bitstream added on 2014-10-03T16:27:37Z : No. of bitstreams: 2 lemos_ff_dr_guara_parcial.pdf.txt: 11034 bytes, checksum: 59c288b2b373bbe58255effddd89bb52 (MD5) 000671151.pdf: 2407167 bytes, checksum: 0e13b6a8dfac5d68060ec4460476f509 (MD5) Bitstreams deleted on 2014-10-03T16:33:14Z: 000671151.pdf,Bitstream added on 2014-10-03T16:43:28Z : No. of bitstreams: 2 lemos_ff_dr_guara_parcial.pdf.txt: 11034 bytes, checksum: 59c288b2b373bbe58255effddd89bb52 (MD5) 000671151.pdf: 2407167 bytes, checksum: 0e13b6a8dfac5d68060ec4460476f509 (MD5) Bitstreams deleted on 2014-10-03T16:48:54Z: 000671151.pdf,Bitstream added on 2014-10-03T16:49:46Z : No. of bitstreams: 1 000671151.pdf: 2407167 bytes, checksum: 0e13b6a8dfac5d68060ec4460476f509 (MD5) Bitstreams deleted on 2014-10-27T11:47:07Z: 000671151.pdf,Bitstream added on 2014-10-27T11:48:04Z : No. of bitstreams: 1 000671151.pdf: 2407167 bytes, checksum: 0e13b6a8dfac5d68060ec4460476f509 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A desidratação do núcleo pulposo que, juntamente com o anulus fibroso, compõe o disco intervertebral, participa do processo de degeneração da coluna vertebral. Torna-se importante entender como este processo de desidratação e a consequente alteração das propriedades mecânicas influenciam na biomecânica dessa articulação. O principal objetivo deste estudo é analisar a influência da desidratação no coeficiente de amortecimento viscoso e como esta variação pode alterar o comportamento mecânico do disco intervertebral lombar. Este estudo é composto de duas etapas: na primeira, o coeficiente de amortecimento viscoso foi obtido experimentalmente de unidades funcionais de colunas lombares suínas antes e após o processo de desidratação das mesmas; na segunda, foi simulado em modelo computacional a resposta harmônica, utilizando-se dados da literatura e do coeficiente de amortecimento viscoso, analisando as diferenças entre uma simulação com o disco intervertebral hidratado e desidratado. O coeficiente de amortecimento viscoso hidratado (4,7) e desidratado (2,7) apresentou diferença estatisticamente significante (p<0,001). Na simulação computacional podese evidenciar uma menor influência da variação do coeficiente de amortecimento viscoso quando analisado de forma isolada do que quando analisado em conjunto com variações nos dados referentes à rigidez, principalmente nas frequências de ressonância e nas amplitudes de pressão intradiscal e deformação do disco intervertebral. Concluiu-se que discos intervertebrais desidratados respondem de forma diferente à vibração, o que pode contribuir para os processos lesivos da coluna vertebral / The dehydration of the nucleus pulposus which, with the anulus fibrosus, composes the intervertebral disc, participates in the process of degeneration of the spine. It is important to understand how this process and the consequent alteration of dehydration of the mechanical properties influence the biomechanics of this joint. The aim of this study is to analyze the influence of dehydration in the viscous damping coefficient and how this variation can change the mechanical behavior of lumbar intervertebral disc. This study consists of two stages: first, the viscous damping coefficient was obtained experimentally in functional units of porcine lumbar spine before and after the dehydration process of them; second, an harmonic response was simulated in a computer model, using literature data and the viscous damping coefficient, analyzing the differences between a simulation with the hydrated and dehydrated intervertebral disc. The hydrated (4.7) and dehydrated (2.7) viscous damping coefficient showed a statistically significant difference (p <0.001). In the computer simulation, a lower influence of variation of the viscous damping coefficient can be detected when analyzed separately than when analyzed together with variation on stiffness data, especially in the resonance frequencies and in the amplitudes of the intradiscal pressure and deformation of the intervertebral disc. We conclude that dehydrated intervertebral discs respond differently to vibration, what can contribute to the damaging processes of the spine

Herniation of the intervertebral disc is a pathological condition characterized by protrusion of the tissue posterio-laterally, often impinging on the spinal chord or nerve roots. The disease is accompanied by a reduction in the average molecular weight and viscosity of the disc proteoglycans, in excess of that which normally occurs with increasing age. The proteoglycans of disc however have not been examined in terms of the modern concepts of cartilage matrix structure. Bovine nasal cartilage, has been shown to contain proteoglycan aggregates, trapped in the intersticess of a collagen network, which can be dissociated with 4M guanidine hydrochloride into diffusible proteoglycan subunits and a multicomponent "linking" fraction. A similar system was thought to occur in the intervertebral disc. It seemed possible that, if such a system was present in the disc, the reduction in the molecular weight and viscosity of the proteoglycans with increasing age and herniation could be due to a decrease in proteoglycan aggregation. The present study showed that proteoglycan aggregates similar to those of bovine nasal cartilage are found in the human intervertebral disc, but that they only represent 5% of the total proteoglycans in the tissue. In contrast, bovine nasal cartilage contained 70% of the proteoglycans in the aggregated form. A novel modification of the extraction procedure was devised by which it was possible to assess the degree of proteoglycan aggregation. Sequential extraction of the tissue with a weak and strong electrolyte (0.4 M and 4M guanidine hydrochloride) selectively removed non-aggregated and aggregated proteoglycans respectively. This procedure provides a new and rapid method for assessing the degree of proteoglycan aggregation in a variety of connective tissues. The small proportion of aggregate in the disc was almost exclusively located in the annulus fibrosus. Re-aggregation studies suggested that both disc and cartilage contain two proteoglycans, only one of which is capable of forming aggregates. Examination of the proteoglycans in a limited number of discs suggested that the degree of aggregation did not change with increasing age. Since, in addition, aggregates represent only a small proportion of the disc proteoglycans, it appeared unlikely that a decrease in the degree of aggregation could account for the decrease in molecular weight and viscosity of the disc proteoglycans observed with increasing age and/or degenerative disc disease. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Back pain is a common complaint and the origin of this frequently attributed to degenerative disc disease. In the most severe cases, the integrity of the disc and surrounding tissue is lost to such an extent that surgical intervention is necessary. Fusion procedures are commonly used to treat severely degenerated discs. Yet this is known to alter the biomechanics of the operated level, and may create a progression of degenerative decline. Total disc replacement has emerged as a viable treatment but the complexity of the spine is reflected in the clinical results, which trail far behind the success of hip and knee arthroplasty. This may be due to a failure of total disc replacement procedures to restore the natural biomechanics of the spine. The present study has led to the development of a dynamic pre-clinical testing protocol to quantitatively assess the efficacy of disc replacement devices. A six-axis spine simulator was designed and built, and the stiffness matrix testing of porcine lumbar specimens was completed, both with and without an axial preload. Intact specimens were tested, and the testing repeated after a total disc replacement procedure with a DePuy In Motion artificial disc. This is the first study to complete dynamic six-axis spinal testing of this kind. The testing demonstrated the disc replacement device compared favourably with the intact porcine disc both in shear and axial stiffness. However, the low-friction, double ball and socket design of the In Motion device lacks stiffness in the three rotational axes, and it is unstable in lateral bending. Rotations are the primary movements in the spine, and it is crucial if the natural biomechanics are to be restored, that a disc replacement device should replicate the stiffnesses of these axes. The next generation of disc replacement devices feature elastomeric materials that may more closely replicate the natural intervertebral disc. From patents registered with DePuy, this may also be true of the next generation of In Motion disc. This research provides a means to complete standardised performance tests of new spinal devices and lays the foundations for future comparison studies. Additionally, the spine simulator and testing protocol would provide valuable data during the design stage of new total disc replacements, aiding the development of the next generation of artificial discs.

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy