Quantitative analysis of misplaced pedicle screws in the thoracic spine: How much pullout strength is lost?

Leonardo B.C. Brasiliense, Nicholas Theodore, Bruno C.R. Lazaro, Zafar A. Sayed, Fatih Ersay Deniz, Volker K.H. Sonntag, Neil R. Crawford

Research output: Contribution to journalArticlepeer-review

Abstract

Object. The object of this study was to investigate the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of thoracic pedicle screws. Methods. Forty human thoracic vertebrae (T6-11) from human cadavers were studied. Before pedicle screws were inserted, the specimens were separated into 4 groups according to the type of screw used: 1) standard pedicle screw (no cortical perforation); 2) screw with medial cortical perforation; 3) screw with lateral cortical perforation; and 4) "airball" screw (a screw that completely missed the vertebral body). Consistency among the groups for bone mineral density, pedicle diameter, and screw insertion depth was evaluated. Finally, each screw was pulled out at a constant displacement rate of 10 mm/minute while ultimate strength was recorded. Results. Compared with well-placed pedicle screws, medially misplaced screws had 8% greater mean pullout strength (p = 0.482) and laterally misplaced screws had 21% less mean pullout strength (p = 0.059). The difference in mean pullout strength between screws with medial and lateral cortical perforations was significant (p = 0.013). Airball screws had only 66% of the mean pullout strength of well-placed screws (p = 0.009) and had 16% lower mean pullout strength than laterally misplaced screws (p = 0.395). Conclusions. This in vitro study showed a significant difference in mean pullout strength between medial and lateral misplaced pedicle screws. Moreover, airball screws were associated with a significant loss of pullout strength.

Original languageEnglish (US)
Pages (from-to)503-508
Number of pages6
JournalJournal of Neurosurgery: Spine
Volume12
Issue number5
DOIs
StatePublished - May 2010
Externally publishedYes

Keywords

  • Cadaver
  • Misplacement
  • Pedicle screw
  • Pullout strength
  • Thoracic spine

ASJC Scopus subject areas

  • Surgery
  • Neurology
  • Clinical Neurology

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