Pullout force of minimally invasive surgical and open pedicle screws

a biomechanical cadaveric study

Phoebe G. M. Matthews, Joseph Cadman, Janos Tomka, Danè Dabirrahmani, Richard Appleyard, Andrew Kam

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Abstract

Background: To assess whether lumbar pedicle screw placement with a minimally invasive surgical (MIS) vs. open technique imparts different biomechanical parameters and thus may affect failure rates.

Methods: Human cadaveric disarticulated lumbar vertebrae 1-5 were stabilised in cement. Pedicle screws were inserted either via the 'MIS' or 'open' technique, based on previously described anatomical landmarks. Each vertebra had one 'MIS' and one 'open' technique screw. Specimens were tested with an Instron mechanical testing machine, positioned to allow for testing of direct coaxial force. Load was applied until failure occurred, and load-displacement curves generated for each screw.

Results: Average failure load was found to be 685±399 N for MIS, versus 661±323 N for open technique (P=0.75). The average ultimate failure load was 748±421 N for MIS, versus 772±326 N for open (P=0.74). Average displacement until failure was 0.95±0.49 mm for MIS as compared to 0.95±0.62 mm for open (P=0.996). Axial stiffness was 936±217 N/mm for MIS and 1,016±263 N/mm for open (P=0.19). Average work required to result in failure was 0.84±1.09 J for MIS and 0.82±1.05 J for open (P=0.94).

Conclusions: There was no significant difference in the biomechanical properties of the MIS as compared with open lumbar pedicle screws, when tested until failure under direct coaxial force. The clinical implication may be that there is no significant advantage in the biomechanical properties of MIS versus open lumbar pedicle screw insertion techniques.

Original languageEnglish
Pages (from-to)3-12
Number of pages10
JournalJournal of Spine Surgery
Volume6
Issue number1
DOIs
Publication statusPublished - Mar 2020

Bibliographical note

Copyright the Publisher 2020. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • Pedicle screw
  • pullout test
  • lumbar instrumentation
  • insertion technique

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