Micromechanical assessment of regional variation in the human lumbar interlamellar matrix

Author: Ali Kaissi

Kaissi, Ali, 2022 Micromechanical assessment of regional variation in the human lumbar interlamellar matrix, Flinders University, College of Science and Engineering

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The lumbar ILM contributes to the overall structural integrity of the intervertebral disc, providing strength and resistance at the boundary between adjacent lamellae, a common site for failure initiation. While there have been previous studies to determine the mechanical properties of the ILM within other species or within human through indirect techniques, the mechanical properties of the human ILM are still predominantly unknown. Gaining a deeper knowledge of the mechanical properties of the human ILM will permit more accurate computational models of the spine in addition to more anatomically accurate future implant design. This study aimed to directly measure the human lumbar ILM micromechanical properties in healthy specimens in both the anatomical radial (tension) and circumferential (shear) loading directions. Regional variations were assessed by obtaining specimens from various circumferential (anterior and posterolateral) and radial (inner and outer) locations within the disc and the viscoelastic behaviour (modulus and energy absorption) assessed by applying the load under three distinct strain rates. The failure mechanics were also investigated through ultimate stress and strain analyses. Extensive pilot testing was conducted on ovine specimens to verify the procedure repeatability prior to the work done on human tissue. Radial and circumferential regional variations were identified with increased modulus and strength in the outer and anterolateral regions in comparison to inner and posterolateral regions, respectively. Viscoelastic properties of the human ILM were confirmed with a strong strain rate dependence. Furthermore, loading direction had a significant effect on the modulus and ultimate stress, with specimens displaying increased modulus under circumferential shear in comparison to radial tension, and radial tension resulting in a greater ultimate stress. These findings provide a new understanding of the human ILM mechanics as a robust basis for future investigation within the field.

Keywords: Biomechanics, Human, Spine, Intervertebral disc, Interlamellar matrix, Lamellae, elastic fibre, micromechanical

Subject: Engineering thesis

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