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Title: Biomechanics of intervertebral disc pain
Author: Stefanakis, Manos
ISNI:       0000 0004 2725 203X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2011
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'Background: Back pain is strongly (but variably) associated with degeneration of intervertebral discs. Mechanical loading has long been considered one of the causes of disc pathology and pain, but its precise role is poorly understood. In particular the spatial relation between load distribution inside the disc, the disc matrix changes as a result of load and their relationship with pain has not been researched. Methods: Distribution of compressive stress inside intervertebral discs from all regions of the spine was studied using stress profilometry in cadaveric motion segments. Matrix pathological changes were studied using simple histology and light microscopy in two groups of surgically removed discs: 'painful' discs from patients undergoing surgery for suspected discogenic pain, and 'control' discs from patients undergoing surgery for scoliosis or spondylolisthesis reduction. Ingrowth of nerves and blood vessels into the annulus was studied by immunohistochemistry with an endothelial and a general neuronal marker. Stress reduction inside annulus fissures were investigated using stress profilometry. Proteoglycan reduction within annulus fissures was studied by means of a novel, semi-quantitative method involving simple histology and image analysis. Although semi-quantitative, the technique had great spatial resolution and allowed integration with the results from the mechanical experiments. Results: High stress concentrations were localised in the middle annulus and increased with disc degeneration. Associated stress gradients appeared early in the degeneration process and were not diminished in late stage degeneration when substantial compressive loading is transferred to the neural arch. Nerve and blood vessel ingrowth increased with degeneration, but were confined to the outermost 4mm of the annulus. Other cellular changes such as apoptosis, cellular infiltration and proliferation were mostly confined to the annulus. Annulus fissures were found to represent focal regions of low proteoglycan content, and also of low compressive stress, especially when the nucleus was also decompressed. Conclusions: Results suggest that high stress gradients play an important role in progressive annulus disruption, and that annulus fissures provide a microenvironment that is mechanically and chemically conducive to the ingrowth of nerves and blood vessels. Co-localisation of nerves, blood vessels and stress concentrations in the middle-outer annulus suggest that this is the most likely site of discogenic pain. Pain is associated with annulus disruption and the attempted healing rather than age-related degenerative changes in the nucleus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available