All ETDs from UAB

Advisory Committee Chair

Alan Eberhardt

Advisory Committee Members

David Littlefield

Lee Moradi

Document Type

Thesis

Date of Award

2017

Degree Name by School

Master of Science in Mechanical Engineering (MSME) School of Engineering

Abstract

Proximal junction kyphosis is a condition that can occur after a long spinal fusion, typically seen in deformity correction surgery. Patients are said to exhibit proximal junc-tion kyphosis when the angle between the uppermost instrumented vertebra and two ver-tebra above that is greater than 10°. Proximal junction kyphosis does not always lead to another surgery but can progress and become symptomatic causing pain and discomfort. Symptomatic proximal junction kyphosis is referred to as proximal junction failure, char-acterized by degradation of the adjacent intervertebral disc or collapse of the proximal vertebral body. It is believed that proximal junction kyphosis/failure arises from in-creased stress in the adjacent intervertebral disc due to the lack of movement in the fused vertebrae. A ligamentous thoracic spine model was generated via CT scans for subsequent finite element analysis. A baseline model, non-instrumented model was created along with 16 different spinal fusion models. Fusion models differed in location of stopping point and screw length and diameter in the upper instrumented vertebra. Finite element analysis in ANSYS was used to compare fusion models with an axial compressive load of 500 N in combination with a forward bending moment of 10,500 N•mm. Complications arose from large deformations causing excessive distortion in elements of the annulus fi-brosus. In order to alleviate this error, various methods were employed. Ultimately, the annulus fibrosus was modeled with a Neo Hookean hyperelastic material model fit from experimental uniaxial test data.

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