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The effect of cage positioning on lumbrosacral vertebral endplate failure in compression Labrom, Robert David
Abstract
Anterior column cage or graft subsidence remains a biomechanically and clinically serious problem that affects the performance and patient outcome of any spinal arthrodesis surgery. To assess the best position to place an interbody fusion cage, a posterior interbody fusion construct was simulated. Specifically, the hypothesis to be tested was that two smaller, posterolaterally positioned interbody cages would provide superior construct stiffness and strength in compression. Nine human cadaver spine specimens from L3-S1 were dissected and continuously posteriorly instrumented with pedicle screws and rods. This continuously instrumented construct was then potted in dental cement and plaster of Paris in such a way as to enable sequential individual axial compression testing of each functional spinal unit (FSU) from L3/4 to L5/S1. All specimens were x-rayed, and scanned with DEXA for bone mineral density pre-testing. Stiffness properties of the FSU's with intact disc and without disc were tested. Three patterns of titanium mesh cages were then used to test stiffness and gross failure under compression: one large central, two small central, or two small posterolaterally positioned cages. After digitizing points on the cage and vertebral bodies pre-test, anoptoelectronic camera system was used to track motion of the cage and vertebrae. The compressive stiffness of the construct at all spinal levels was significantly higher with the intact disc compared to without the disc, and with any of the three cage patterns, and these differences were significant. Mean failure loads for the three cage positions ranged between 2000 N and 2500 N and were not significantly different, though tended to be higher for the 2 posterolateral cage position. Mean bone mineral density values for both superior and inferior vertebrae of the FSU tested, were significantly correlated with failure load values, yet did not appear predictive of cage subsidence direction. Motion analysis of the cage- either single or double combinations, revealed no trend for either superior or inferior subsidence into the endplates. Mode of endplate failure appears to involve a mass shear displacement of the underlying trabecular bone, with condensation of the trabecular architecture in the immediate sub-endplate region. Results of this study have supported the biomechanical validity of PLIF and TLIF type surgeries, with the preferred placement of two smaller posterolaterally positioned mesh cages (Harms et al, 1997).
Item Metadata
Title |
The effect of cage positioning on lumbrosacral vertebral endplate failure in compression
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2002
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Description |
Anterior column cage or graft subsidence remains a biomechanically and
clinically serious problem that affects the performance and patient outcome of
any spinal arthrodesis surgery. To assess the best position to place an interbody
fusion cage, a posterior interbody fusion construct was simulated.
Specifically, the hypothesis to be tested was that two smaller, posterolaterally
positioned interbody cages would provide superior construct stiffness and
strength in compression.
Nine human cadaver spine specimens from L3-S1 were dissected and
continuously posteriorly instrumented with pedicle screws and rods. This
continuously instrumented construct was then potted in dental cement and
plaster of Paris in such a way as to enable sequential individual axial
compression testing of each functional spinal unit (FSU) from L3/4 to L5/S1.
All specimens were x-rayed, and scanned with DEXA for bone mineral density
pre-testing. Stiffness properties of the FSU's with intact disc and without disc
were tested. Three patterns of titanium mesh cages were then used to test
stiffness and gross failure under compression: one large central, two small
central, or two small posterolaterally positioned cages.
After digitizing points on the cage and vertebral bodies pre-test, anoptoelectronic
camera system was used to track motion of the cage and vertebrae.
The compressive stiffness of the construct at all spinal levels was significantly
higher with the intact disc compared to without the disc, and with any of the three
cage patterns, and these differences were significant. Mean failure loads for the
three cage positions ranged between 2000 N and 2500 N and were not
significantly different, though tended to be higher for the 2 posterolateral cage
position.
Mean bone mineral density values for both superior and inferior vertebrae of the
FSU tested, were significantly correlated with failure load values, yet did not
appear predictive of cage subsidence direction.
Motion analysis of the cage- either single or double combinations, revealed no
trend for either superior or inferior subsidence into the endplates. Mode of
endplate failure appears to involve a mass shear displacement of the underlying
trabecular bone, with condensation of the trabecular architecture in the
immediate sub-endplate region.
Results of this study have supported the biomechanical validity of PLIF and TLIF
type surgeries, with the preferred placement of two smaller posterolaterally
positioned mesh cages (Harms et al, 1997).
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Extent |
28951625 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-09-16
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0090457
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2002-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.