Graduation Year

2012

Document Type

Thesis

Degree

M.S.B.E.

Degree Granting Department

Chemical Engineering

Major Professor

William E. Lee III

Keywords

Functional Spinal Unit (FSU), In Vitro, Laminectomy Decompression, Range of Motion (ROM), Stenosis

Abstract

Stenosis is one of the most common causes for spinal surgery. Laminectomy decompression and fusion are surgical procedures prescribed for this condition. The intention of this work was to investigate the effects of a laminectomy decompression, followed by fusion, on a lumbar functional spinal unit (FSU) through in vitro dynamic (±8Nm at 0.125Hz) and quasi-static (±7.5Nm at 0.1Hz) biomechanical tests, for flexion, extension, bending and rotation motions.

Six FSUs where disarticulated from four human cadaveric lumbar spines (63 ± 12 years) and were tested under the following sequence: (1) intact, (2) laminectomy decompression, and (3) Pedicle Screw System (PSS), using a load-displacement controlled system. Dynamic neutral zone (NZ), dynamic neutral zone stiffness (NZS) and the range of motion (ROM) were the parameters evaluated.

Since only 6 FSUs from different spinal levels were used, any effect related to the spinal level could not be evaluated. This limitation enforced to consider normalized data (with respect to intact) as an alternative analysis, but large standard deviations after transforming the data forced us to contemplate this "a pilot study".

Dynamic testing revealed that there were no significant differences in the neutral zone magnitude for any motion after a laminectomy decompression, while its magnitude for flexion-extension was significantly affected by PSS treatment (p<0.004). The change in dynamic NZ (normalized data) was significantly different (p<0.03) after both treatments for flexion-extension motion. The reduction in stiffness (normalized data) for extension after a laminectomy, and the increase in stiffness (normalized data) for flexion and extension after PSS treatment, were both significant (p<0.03 and p<0.05, respectively). The ROM were not statistically significant for the three treatments, but normalized data showed significant differences (p<0.05) for all motions, except for right bending after laminectomy and right rotation after PSS.

Non-normalized data from quasi-static testing didn't show any statistically significant difference between the treatments for any motion. Normalized data suggested significant differences for the change in ROM for all motions at multiple load conditions, especially for flexion and extension.

This pilot study suggests there may be a considerable effect of a laminectomy on the stability of a lumbar FSU. Dynamic data suggested the changes in neutral zone stiffness triggered by a laminectomy procedure may be significant for extension. PSS treatment increased segment's NZ stiffness by more than double. The changes in ROM from quasi-static loading caused by a laminectomy decompression may be significant as well, especially for flexion (20%) and extension (greater than 10%).

It is suggested that further studies involving spine biomechanics should consider and report, but not be limited to the following variables: exposure time of the specimen to room temperature, preservation and testing conditions, ligaments and joints conditions, testing protocol, and loading history.

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