Do Mechanical and Structural Characteristics of Degenerated Intervertebral Discs Contribute to Development of Degenerative Scoliosis and Spondylolisthesis?
Date
2023-08-28
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Abstract
Intervertebral disc (IVD) degeneration is the age-related breakdown of the cushioned discs that serve as the principal connection between the vertebral bodies. Although affecting 80% of individuals over the age of 50, the causes of the highly varied severity of this disease are not well understood. Additionally, in some cases, primarily in women, the degeneration of the IVD leads to spinal deformities. Degenerative scoliosis (dScoli), the lateral translation and rotation of the vertebrae, and degenerative spondylolisthesis (dSpondy), the forward slippage of the vertebrae with respect to its caudal neighbour, both potentially lead to immobility and pain. These conditions involve increased instability of motion segments of the spine, cascading into further degeneration. The aim of this study was to compare the shear mechanical behaviour of the annulus fibrosus (AF), the outer portion of the IVD, in normal, non-deformity degenerated (degen), dScoli, and dSpondy patients. Small sections of the AF were collected from healthy donors and surgical patients and sheared, mimicking the translation seen in spinal deformity. These same AF sections were scored for degeneration through histology and their lamellar structure was measured with optical coherence tomography (OCT). From these tests, the structure-function relationship of degenerated AF was analyzed to explore degenerative changes. A reduced shear stiffness in degen samples (radial 27 ± 24 kPa, circumferential 57 ± 43 kPa) when compared to normal tissue (radial 80 ± 38 kPa, circumferential 231 ± 73 kPa) was found (p < 0.05). dScoli tissue were further reduced in shear stiffness (radial 12 ± 6 kPa, circumferential 33 ± 21 kPa), although not significantly. There were significant trends linking an increase in structure degeneration, by histology (rS = -0.58, p < 0.01) and OCT (rS = -0.70, p < 0.01), to decreased circumferential shear modulus. Differences in structure and shear stiffness will serve as the backbone for further research into surgical tissue to better understand the progression of IVD degeneration and spinal deformities. Through understanding of the structure-function relationship of the AF, predictors of outcomes and potential treatments could help patients better manage these painful conditions.
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Keywords
Intervertebral disc, Annulus fibrosus, Scoliosis, Spondylolisthesis, Shear, Histology, Optical coherence tomography
Citation
Bader, T. J. (2023). Do mechanical and structural characteristics of degenerated intervertebral discs contribute to development of degenerative scoliosis and spondylolisthesis? (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.