Biomechanics of thoracic short versus long fixation after 3-column injury: Laboratory investigation

Bruno C.R. Lazaro, Fatih Ersay Deniz, Leonardo B.C. Brasiliense, Phillip M. Reyes, Anna G.U. Sawa, Nicholas Theodore, Volker K.H. Sonntag, Neil R. Crawford

Research output: Contribution to journalArticlepeer-review

Abstract

Object. Posterior screw-rod fixation for thoracic spine trauma usually involves fusion across long segments. Biomechanical data on screw-based short-segment fixation for thoracic fusion are lacking. The authors compared the effects of spanning short and long segments in the thoracic spine. Methods. Seven human spine segments (5 segments from T-2 to T-8; 2 segments from T-3 to T-9) were prepared. Pure-moment loading of 6 Nm was applied to induce flexion, extension, lateral bending, and axial rotation while 3D motion was measured optoelectronically. Normal specimens were tested, and then a wedge fracture was created on the middle vertebra after cutting the posterior ligaments. Five conditions of instrumentation were tested, as follows: Step A, 4-level fixation plus cross-link; Step B, 2-level fixation; Step C, 2-level fixation plus cross-link; Step D, 2-level fixation plus screws at fracture site (index); and Step E, 2-level fixation plus index screws plus cross-link. Results. Long-segment fixation restricted 2-level range of motion (ROM) during extension and lateral bending significantly better than the most rigid short-segment construct. Adding index screws in short-segment constructs significantly reduced ROM during flexion, lateral bending, and axial rotation (p < 0.03). A cross-link reduced axial rotation ROM (p = 0.001), not affecting other loading directions (p > 0.4). Conclusions. Thoracic short-segment fixation provides significantly less stability than long-segment fixation for the injury studied. Adding a cross-link to short fixation improved stability only during axial rotation. Adding a screw at the fracture site improved short-segment stability by an average of 25%.

Original languageEnglish (US)
Pages (from-to)226-234
Number of pages9
JournalJournal of Neurosurgery: Spine
Volume14
Issue number2
DOIs
StatePublished - Feb 1 2011
Externally publishedYes

Keywords

  • 3-column injury
  • Pedicle screw
  • Short-segment fixation
  • Thoracic fixation

ASJC Scopus subject areas

  • Surgery
  • Neurology
  • Clinical Neurology

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