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Spine J. 2013 Dec;13(12):1934-9. doi: 10.1016/j.spinee.2013.03.046. Epub 2013 May 14.

Primary stability of pedicle screws depends on the screw positioning and alignment.

Author information

1
Department of Neurosurgery, Humanitas Clinical and Cancer Research Center, Via Manzoni 56, 20089 Rozzano (MI), Italy. Electronic address: f.costa@fastwebmail.it.

Abstract

BACKGROUND CONTEXT:

There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws.

PURPOSE:

The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations.

METHODS:

Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system.

RESULTS:

Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position.

CONCLUSIONS:

These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment.

KEYWORDS:

Pedicle screw; Porcine; Pullout; Screw misplacement; Stability

PMID:
23684239
DOI:
10.1016/j.spinee.2013.03.046
[Indexed for MEDLINE]
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