STUDY DESIGN: Biomechanical cadaver study. OBJECTIVES: The purpose of our study was to compare the pullout strength of standard, expandable, and cement-augmented pedicle screws. SUMMARY OF BACKGROUND DATA: 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.
STUDY DESIGN: Biomechanical cadaver study. OBJECTIVES: The purpose of our study was to compare the pullout strength of standard, expandable, and cement-augmented pedicle screws. SUMMARY OF BACKGROUND DATA: 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.