Date on Master's Thesis
12-2025
Document Type
Master's Thesis
Degree Name
M. Eng.
Department
Bioengineering
Committee Chair
Roussel, Thomas
Committee Co-Chair (if applicable)
Voor, Michael
Committee Member
Williams, Stuart J.
Committee Member
Chen, Joseph
Author's Keywords
pedicle screw loosening; cyclic axial loading; stiffness decay; displacement; bone surrogate strength; failure
Abstract
Pedicle screw loosening is a common failure mode in spinal instrumentation, particularly in osteoporotic bone, where cancellous strength averages 0.944 MPa compared to 1.5-7.8 MPa in healthy bone. This study evaluated toggle-out testing for predicting pedicle screw failure and examined how material strength affects failure behavior. Polyurethane blocks underwent progressive cyclic loading from 100 N to 400 N in 100 N increments, with displacement recorded throughout. A 200 N load reflects forces typically carried by a screw during walking in an osteoporotic patient, placing the test range within expected clinical loading. Displacement behavior and stiffness decay were quantified using a power-law model. Weaker blocks (4.9 and 5.85 MPa) exhibited greater displacement accumulation and earlier severe stiffness degradation, while stronger blocks (8.4 and 9.85 MPa) remained stable through higher load levels. These combined metrics identified strength-specific failure thresholds and demonstrated the importance of material strength in predicting screw fixation stability.
Recommended Citation
Shelby, Rebecca Elayne, "Evaluating toggle-out testing for pedicle screw failure prediction" (2025). Master of Engineering Theses. Paper 7.
Retrieved from https://ir.library.louisville.edu/speed_meng/7
