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EFFECT OF PROGRESSIVE INCREASE IN RADIAL LESION SIZE ON LUMBAR INTERVERTEBRAL DISC BIOMECHANICS DEPENDS ON THE INTEGRITY OF SURROUNDING ANNULAR FIBERS: 38.

Natarajan, R N.1; Qasim, M.2; An, H1; Andersson, G B J.1

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Spine Journal Meeting Abstracts: October 2010 - Volume - Issue - p 38
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INTRODUCTION: Among different phenomena that occur during disc degeneration, annular radial tears are commonly associated with disc herniations. It is hypothesized that change in disc flexibility due to progressive increase in size of radial tear will depend on the integrity of surrounding annular fibers.

METHODS: Progression of annular tears was created in a poro‐elastic finite element model of L4/5 by modifying material property (from annular ground substance to nucleus material) at two “integrating” points at a time in each annular finite element along the radial direction in the left lateral posterior quadrant. Annular fibers either around the tear region or in the entire vicinity were also removed. Models with radial tears occupying 0.0% to 0.3% of total annulus volume were created and loaded with 1200 N compression combined with moments of 7.5 Nm in all the three principal planes in both directions.

RESULTS: Percent increase in range of motion varied from 0% to 0.4 % (for various loading modes) when the annular fibers near the tear region were only removed. A larger increase in range of motion (varying from 0% to 4.0%) was seen when fibers in the entire vicinity of the tear were removed. For example, percent increase in motion under left torsion was 20 times larger when annular fibers in the entire vicinity were removed as compared to removing fibers only around the tear region.

CONCLUSIONS: Current study validated the hypothesis that change in disc flexibility due to progressive increase in size of radial tear will depend on the integrity of surrounding annular fibers. The study showed that radial annular incision will propagate much faster if the annular fibers in the vicinity of the tear region (in contrast to fibers near the tear region) are not able to sustain load.

ACKNOWLEDGEMENT: NIH AR48152‐02

© 2010 Lippincott Williams & Wilkins, Inc.