Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Kinesiology

Faculty/School

Faculty of Science

First Advisor

Dr. Diane Gregory

Advisor Role

Dissertation Advisor

Abstract

The capacity for fractures to manifest in the growth cartilage of the adolescent human spine is well documented, but much of the knowledge available regarding such fractures remains retrospective and is largely composed of small case series made up of relatively few participants. In-vitro tissue testing has demonstrated that pressurization of the intervertebral disc’s nucleus pulposus significantly contributes to the generation of growth plate fractures. However, a comprehensive biomechanical investigation of the mechanical consequences for the intervertebral disc when exposed to ring apophyseal (growth plate) fractures at different velocities remains to be demonstrated.

The first two experiments of the present dissertation employed rapid internal pressurization, and quasi-static compression to generate fractures in a porcine cervical model of the spine. When rapidly pressurized, regardless of a resulting fracture or not, lamellar adhesion in the annulus was impaired compared to non-pressurized spines. Conversely, when loading was applied quasi-statically, annular mechanical properties were unaffected in both fracture-induced and non-fracture induced samples compared to control. It was therefore concluded that annulus damage is largely mediated by the velocity of loading rather than simply the application of compression and occurrence of a fracture.

Experiments three and four investigated the visual integrity of the annulus fibrosus and vertebral bodies, using histological assessment at 10x and 100x magnification, and micro computed tomography scans, respectively. The histological analysis corroborated the findings in the first set of studies; specifically, damage to the annulus at the microscopic level was most prominent in the rapidly loaded spines and least noticeable in the quasi-static compression samples. Visually, at both 10x and 100x magnifications, histology reported significantly greater visual disorganization inhabiting the annulus fibrosus following the application of the rapid pressurization stimulus, and this observation was made whether growth plate fracture was visualized or not. Importantly, neither micromechanical testing (p values for interlamellar matrix and bilayer tensile variables all >0.05; N=24 total motion segments), nor histological assessment, demonstrated significant injury to the annulus fibrosus when growth plate fractures were accomplished at a quasi-static velocity via compression.

Micro computed tomography further confirmed the clinical relevance of fractures generated using both the rapid pressurization and quasi-static modalities and likened their morphology to that observed in the adolescent human.

The use of multiple investigation methods in the present dissertation strengthens its conclusions by triangulating results across a broad range of assessment procedures, each of which is currently employed by the research field. In addition, the strong morphological resemblance between fractures accomplished in the present dissertation’s porcine cervical model, and the human adolescent spine, strongly recommend this animal model for future study of this fracture entity, when human tissue is unavailable. The final study of this dissertation is a review of the current literature regarding fracture occurrence and biomechanics as they pertain to the skeletally immature human spine. The purpose of the review is to integrate the findings from the experimental studies of this present dissertation, into the broader scope of vertebral fracture biomechanics in the human spine. Results from the present dissertation demonstrate that the velocity at which ring apophyseal fracturs occur in the spine represents a significant variable with regards to the mechanical and visual integrity of the intervertebral disc’s annulus fibrosus, even when a similar morphology of growth plate fracture is present. The current clinical and surgical treatment paradigms do little to differentiate patients along the lines of injury mechanism, but the present dissertation hopes to prompt future investigations into the velocity-mediated injury mechanisms, potentially inhabiting the adolescent human spine.

Convocation Year

2023

Convocation Season

Fall

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Available for download on Saturday, August 15, 2026

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