Screw omission and the stability of posterior pedicle screw constructs for short-segment stabilization

Joseph Y. Margulies, Robert S. Casar, Michael G. Neuwirth, Shaul D. Margulies, Fred J. Kummer

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


To determine the net contribution of a spinal construct to stability, and whether extending the construct to another level in situations in which a defective pedicle cannot have a screw inserted, we performed biomechanical tests in which we evaluated three-, four-, and five-level synthetic spinal constructs in which the location and number of pedicle screws were varied above and below a vertebrectomy defect. We subjected all constructs to axial, compression, lateral bending, flexion, extension, and torsional forces with the use of an Instron biaxial machine. Left-right symmetrical constructs were more stable than asymmetrical ones. Three-level constructs were statistically stiffer than the longer ones in compression, left bending, and flexion. Torsional stability, however, was greater in the longer constructs. Five- level constructs with both end screws in place had greater torsional stiffness than when they were missing a screw. In vertebrectomy defects, if four screws cannot be placed across it, then the engagement of two screws is indicated. The stability provided by a single screw at a spinal level is minimal. Additional screws augment the purchase of the construct in the bone; however, they do not afford further protection to the defect.

Original languageEnglish
Pages (from-to)240-245
Number of pages6
JournalJournal of Spinal Disorders
Issue number3
StatePublished - 1997
Externally publishedYes


  • Biomechanics
  • Fixation
  • Lumbar vertebral bodies
  • Pedicular screws
  • Screw omission
  • Short segment constructs
  • Spine


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