Date of Award

5-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biomedical Engineering and Imaging

Research Advisor

Denis J. DiAngelo, Ph.D.

Committee

Brian P. Kelly, Ph.D. Gladius Lewis, Ph.D.

Abstract

The facet joints of the lumbar spine are one of the sources of low‑back pain that affects a great portion of the population. Minimally‑invasive (MI) procedures have been becoming more popular in the surgical decompression of the spine because they offer shorter recovery time and involve removal of smaller amounts of important structures. With these features, it is believed that MI procedures lead to less clinical instability, and the functionality of the segment is maintained. Another important factor is how the facet angle in the lumbar segments affects the biomechanical instability. In spite of all this interest in MI procedures, there is little biomechanical research to back these claims. Therefore, in this study two MI procedures were compared with the laminectomy, the gold‑standard for lumbar decompression. Eight lumbar cadaveric motion segment units were procured, mounted, and tested intact, and then following MI unilateral facetectomy (UF), MI bilateral facetectomy (BF), and a traditional laminectomy (TL) using three different loading scenarios. The three different loading scenarios utilized in this study were the pure moment (PM), combined loading and moment (CLM), and the coupled‑eccentric loading (CEL) protocols. The PM testing protocol is the standard form of biomechanical testing of the spine. The CLM testing protocol introduced compressive and shear forces to increase translation in the sagittal plane. The CEL protocol was used because it combined a sagittal bend with a forced axial rotation. Rotational values were analyzed at the end limit of 8 Nm for flexion and extension and at 6 Nm for left and right lateral bending. Translations under PM and CLM were calculated utilizing a simulation software Visual Nastran. The criterion for instability was used to see if UF, BF, and TL met this criterion as compared to what would be clinically seen radiographically. In addition to these biomechanical data, CT images were analyzed to determine the change in the facet angle, contact area of the facet, and length of the joint removed after the BF. Increased motion was seen in the BF and TL compared to the harvested spine condition in all protocols. A decrease in rotation was seen in the UF condition in all protocols, with the exceptions being in right lateral for PM. None of the PM and CLM data met the criteria for instability. A decrease in facet angle, contact area, and length of the facet after the BF was observed. The TL had the most number of significant biomechanical increases when compared to the harvested condition, making it a less favorable surgical procedure when compared to each of the MI procedures. No studies have used the multiple loading scenarios, have quantified the amount of instability, or have taken account the amount of resection and change in facet angle due to MI procedures. Further investigation of the biomechanical effects of the MI procedures is still needed to gain more insight on how MI procedures affect spine biomechanics.

DOI

10.21007/etd.cghs.2011.0281

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