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Updated: May 30, 2026
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An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model
Published on: May 31, 2017
A titanium expandable pedicle screw improves initial pullout strength as compared with standard pedicle screws.
Srilakshmi Vishnubhotla1, William B McGarry, Andrew T Mahar
1Biomechanical and Clinical Research, Alphatec Spine Inc., 5818 El Camino Real, Carlsbad, CA 92008, USA.
Summary
Expandable titanium pedicle screws offer enhanced stability in osteoporotic bone compared to standard screws. This study found improved pullout strength, crucial for spinal fusion success in aging populations.
Area of Science:
- Orthopedic Surgery
- Biomedical Engineering
- Spinal Biomechanics
Background:
- Pedicle screws are standard for spinal arthrodesis, providing critical stabilization.
- Aging-related bone density loss compromises screw fixation, increasing risks of pullout and pseudarthrosis.
- Modified pedicle screw designs may enhance stability in weakened bone.
Purpose of the Study:
- To compare the initial pullout strength of expandable titanium pedicle screws against standard titanium pedicle screws.
- To assess biomechanical differences in screw fixation under load.
Main Methods:
- In vitro biomechanical investigation using human cadaveric thoracolumbar spines.
- Quantitative computed tomography (CT) for bone density assessment (DXA T-scores).
- Axial pullout testing of standard and expandable pedicle screws at 25 mm/min, analyzing stiffness, yield load, ultimate load, and energy absorption.
Main Results:
- Expandable screws showed a statistically significant ~30% greater ultimate load compared to standard screws (p<.05).
- Energy required for failure was significantly higher for expandable screws (p<.0001).
- No significant difference in stiffness; expandable screws approached 25% greater yield load.
Conclusions:
- Expandable titanium pedicle screws provide superior pullout stability in osteopenic/osteoporotic bone.
- Findings suggest potential benefits for spinal arthrodesis in patients with reduced bone density.
- Further research on diverse loading conditions is recommended to fully evaluate expandable screw stability.
