A biomechanical comparison of sacral pedicle screw salvage techniques.
METHODS
Biomechanical cadaver study.


OBJECTIVE
The purpose of our study was to compare the pullout strength of standard, expandable, and cement-augmented pedicle screws.


BACKGROUND
Salvage procedures are needed to restore the stability of lumbosacral arthrodesis when pedicle screw fixation in the sacrum fails.


METHODS
Thirteen pairs of sacral (S1) pedicles were implanted initially with 7-mm tapped monoaxial stainless steel pedicle screws (Moss Miami, Depuy Spine, Raynham, MA) inserted under fluoroscopy with bicortical purchase. The screws were distracted axially at a rate of 6 mm/min to measure pullout strength. One pedicle of each pair was assigned randomly to be revised with an expandable pedicle screw (omega-21 Spinal Fixation System, EBI Medical Systems, Parsippany, NJ); the contralateral pedicle was revised with a screw augmented with polymethylmethacrylate (Simplex P, Howmedica, Mahwah, NJ). The screws then were retested as before to measure pullout strength.


RESULTS
Expandable screws (391 +/- 28 N) and polymethylmethacrylate-augmented screws (599 +/- 28 N) exhibited significantly greater pullout strength than their respective initial standard pedicle screws (145 +/- 28 N and 156 +/- 28 N).


CONCLUSIONS
Our results suggest that expandable pedicle screws may provide sufficient fixation, but these results need clinical verification.
Department of Orthopaedic Surgery, University of Maryland School of Medicine, Baltimore, MD, USA.
Bonaventure B
BB
Ngu
Stephen M
SM
Belkoff
Daniel E
DE
Gelb
Steven C
SC
Ludwig
D000368:Aged; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000592:standards; D001863:Bone Screws / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D008422:Materials Testing / Q000295:instrumentation / Q000592:standards; D008875:Middle Aged; D012447:Sacrum / Q000473:pathology / Q000502:physiology* / Q000601:surgery*