Electronic Thesis and Dissertation Repository


Master of Science


Medical Biophysics


Dr. Chris Bailey


Pedicle screws are commonly utilized in spinal surgery; however, traditional designs often do not provide adequate fixation in osteoporotic spines. The objective of this thesis was to develop a novel expanding screw for use in osteoporotic lumbar pedicles. Helical screws capable of expanding post insertion were built on a rapid prototype machine. A materials testing machine performed axial load to failure tests in both Sawbones and cadaveric specimens comparing the new design to traditional screws (rate = 10mm/min to 20 mm). Output parameters included yield load, ultimate load, stiffness, energy to failure and total energy. The expanding screw showed a 36% increase in total energy (p=0.02), but no other differences were identified. Based on this initial design, the expandable pedicle screws failed to demonstrate improved screw pullout; however, differences may be observed in other loading modes (i.e., toggle) and further design modifications and improvements in post-build machining may provide beneficial enhancements.