Biomechanics of transvertebral screw fixation in the thoracic spine: An in vitro study

Nestor G. Rodriguez-Martinez, Amey Savardekar, Eric W. Nottmeier, Stephen Pirris, Phillip M. Reyes, Anna G U S Newcomb, George A C Mendes, Samuel Kalb, Nicholas Theodore, Neil R. Crawford

Research output: Contribution to journalArticle

Abstract

OBJECTIVE: Transvertebral screws provide stability in thoracic spinal fixation surgeries, with their use mainly limited to patients who require a pedicle screw salvage technique. However, the biomechanical impact of transvertebral screws alone, when they are inserted across 2 vertebral bodies, has not been studied. In this study, the authors assessed the stability offered by a transvertebral screw construct for posterior instrumentation and compared its biomechanical performance to that of standard bilateral pedicle screw and rod (PSR) fixation. METHODS: Fourteen fresh human cadaveric thoracic spine segments from T-6 to T-11 were divided into 2 groups with similar ages and bone quality. Group 1 received transvertebral screws across 2 levels without rods and subsequently with interconnecting bilateral rods at 3 levels (T8-10). Group 2 received bilateral PSR fxation and were sequentially tested with interconnecting rods at T7-8 and T9-10, at T8-9, and at T8-10. Flexibility tests were performed on intact and instrumented specimens in both groups. Presurgical and postsurgical O-arm 3D images were obtained to verify screw placement. r e sU lt s: The mean range of motion (ROM) per motion segment with transvertebral screws spanning 2 levels compared with the intact condition was 66% of the mean intact ROM during fexion-extension (p = 0.013), 69% during lateral bending (p = 0.015), and 47% during axial rotation (p < 0.001). The mean ROM per motion segment with PSR spanning 2 levels compared with the intact condition was 38% of the mean intact ROM during flexion-extension (p < 0.001), 57% during lateral bending (p = 0.007), and 27% during axial rotation (p < 0.001). Adding bilateral rods to the 3 levels with transvertebral screws decreased the mean ROM per motion segment to 28% of intact ROM during flexion-extension (p < 0.001), 37% during lateral bending (p < 0.001), and 30% during axial rotation (p < 0.001). The mean ROM per motion segment for PSR spanning 3 levels was 21% of intact ROM during flexion-extension (p < 0.001), 33% during lateral bending (p < 0.001), and 22% during axial rotation (p < 0.001). CONCLUSIONS: Biomechanically, flxation with a novel technique in the thoracic spine involving transvertebral screws showed restoration of stability to well within the stability provided by PSR flxation.

Original languageEnglish (US)
Pages (from-to)187-192
Number of pages6
JournalJournal of Neurosurgery: Spine
Volume25
Issue number2
DOIs
StatePublished - Aug 1 2016
Externally publishedYes

Keywords

  • Posterior instrumentation
  • Thoracic spine
  • Transvertebral screws

ASJC Scopus subject areas

  • Medicine(all)

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  • Cite this

    Rodriguez-Martinez, N. G., Savardekar, A., Nottmeier, E. W., Pirris, S., Reyes, P. M., Newcomb, A. G. U. S., Mendes, G. A. C., Kalb, S., Theodore, N., & Crawford, N. R. (2016). Biomechanics of transvertebral screw fixation in the thoracic spine: An in vitro study. Journal of Neurosurgery: Spine, 25(2), 187-192. https://doi.org/10.3171/2015.11.SPINE15562