Assessing the effect of degeneration on the human lumbar inter-lamellar matrix

Author: Ushmita Devi Reebye

Reebye, Ushmita Devi, 2022 Assessing the effect of degeneration on the human lumbar inter-lamellar matrix, Flinders University, College of Science and Engineering

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Disc degeneration of the lumbar spine is considered as one of the underlying factors of low back pain (LBP). LBP caused by disc degeneration is known to affect an increasing number of people over 60 years each year. LBP is a billion-dollar problem that has become a huge socioeconomic burden in many countries, making it a global health threat. To date, there is little understanding of the underlying mechanism of disc degeneration from a micro-mechanical point of view. Therefore, the aim of this study was to investigate the effect of degeneration on the micromechanical properties of human inter-lamellar matrix (ILM). The ILM is the boundary between lamellae and is thought to be the weakest structure of the disc. As a result, when the disc is under compressive loads, the region at highest risk of failure is the ILM. The purpose of this research is to determine the viscoelastic and failure properties of the ILM. A validated testing method was adapted using a micromechanical testing machine to measure the viscoelastic and failure properties of the ILM in healthy and degenerated discs. The outer anterior and posterolateral region of each disc was separated, sliced and loaded under three different strain rates of 0.1%/s (slow), 1%/s (medium) and 10%/s (fast). Uniaxial testing in tension (radial) and shear (circumferential) directions was preformed, followed by failure tests. Outcome measures of modulus and energy absorption (hysteresis loss coefficient) were obtained from the dynamic tests, followed by the failure test parameters of failure stress and toughness. The anisotropic structure of the ILM was confirmed since different behaviors of tensile and shear modulus were observed for both healthy and degenerated discs. In addition, when disc regions were compared, both tensile and shear modulus were lower in the posterolateral region indicating that this region was more susceptible to failure. When tested to failure, the ILM demonstrated a significantly lower failure shear stress compared to tensile stress, thus supporting the understanding that discs are more vulnerable under shear stresses. The results of this study enhanced our knowledge about the mechanics of the ILM in healthy and degenerated discs and can be used for a better understanding of the initiation and progression of delamination that result in degeneration.

Keywords: ILM, disc, degeneration, inter-lamellar matrix, low back pain, micromechanical testing, microstructure

Subject: Engineering thesis

Thesis type: Masters
Completed: 2022
School: College of Science and Engineering
Supervisor: John J. Costi