The spine journal : official journal of the North American Spine Society
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The intervertebral disc plays a major functional role in the spinal column, providing jointed flexibility and force transmission. The end plate acts as an important structural transition between the hard vertebral tissues and the compliant disc tissues and is therefore a region of potentially high stress concentration. The effectiveness of anchorage of the tough annulus fibers in the end plate will have a major influence on the overall strength of the motion segment. Failure of the end plate region is known to be associated with disc herniation. ⋯ Given both the limited thickness of the end plate and the intrinsic strength of the interface bond between bundle and end plate matrix, the branched morphology is consistent with a mechanism of optimal shear stress transfer wherein a greater strength of annular fiber anchorage can be achieved over a relatively short insertion distance.
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Present studies concerning the safety and reliability of neurophysiological monitoring during thoracic pedicle screw placement remain inconclusive, and therefore, universally validated threshold levels that confirm osseous breakage of the instrumented pedicles have not been properly established. ⋯ In the experimental animals, the observed electrical impedance depended on the distance of screws from the neural structures and not on the integrity of the pedicle cortex. The screw-triggered EMG technique did not reliably discriminate the presence or absence of bone integrity after pedicle screw placement. The response intensity was not related to the type of interposed tissue.