Title

Pullout resistance of thoracic extrapedicular screws used as a salvage procedure

Document Type

Article

Abstract

Background context: Extrapedicular screws are placed more laterally than intrapedicular screws and pass through the transverse process or rib head before entering the vertebral body. These screws are sometimes placed to salvage failed pedicle screws, but the change in pullout resistance of extrapedicular screws after salvage has not been quantified. Purpose: To quantify the pullout resistance of thoracic extrapedicular screws compared with intrapedicular screws and the pullout resistance of newly inserted screws compared with extrapedicular screws used as salvage for failed intrapedicular screws. Study design: In vitro paired comparison of screw pullout resistance in isolated thoracic vertebrae. Methods: Tapered monoaxial pedicle screws were inserted in the left or right pedicle of 11 human cadaveric thoracic vertebrae. An extrapedicular screw was inserted on the contralateral side. Both screws were pulled out axially at 0.5 mm/s using a servohydraulic test frame while applied load was recorded. Then a fresh extrapedicular screw was inserted as a salvage screw on the intrapedicular screw side and pulled out. Results: In uncompromised vertebrae, the pullout strength of extrapedicular screws was 80±32% of that of intrapedicular screws (p=.073, repeated-measures one-way analysis of variance/Tukey). Salvage screws restored pullout strength to 65±30% of that of intrapedicular screws (p=.003). Conclusions: Extrapedicular screws provided comparable but slightly lower pullout resistance to intrapedicular screws in uncompromised vertebrae. They are therefore a feasible salvage technique when a compromised pedicle precludes reinsertion of an intrapedicular screw, but the salvage screw is significantly weaker than the original screw. © 2007 Elsevier Inc. All rights reserved.

Publication Date

5-1-2007

Publication Title

Spine Journal

ISSN

15299430

Volume

7

Issue

3

First Page

286

Last Page

291

PubMed ID

17482111

Digital Object Identifier (DOI)

10.1016/j.spinee.2005.12.007

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