Analyzing Pedicle Screw Strength with Finite Element Method in Relation to Vertebral Bone Properties

by Jefrem Schwab
Doctoral thesis
Date of Examination:2025-01-15
Date of issue:2025-01-13
Advisor:Prof. Dr Arndt F. Schilling
Referee:Prof. Dr Arndt F. Schilling
Referee:PD Dr. Henning Dathe
Persistent Address: http://dx.doi.org/10.53846/goediss-10994

 

 

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Abstract

English

Vertebral fractures are increasingly prevalent in our aging population. Conservative treatments and minimally invasive surgeries are standard, but posterior fixation systems like pedicle-screw-rod constructs face failure risks such as screw loosening, primarily caused by age-related diminished bone quality and osteoporosis. This poses significant challenges for individuals and healthcare systems. This study developed simplified models of healthy and osteoporotic vertebrae, characterized by a 50% reduction in cortical thickness and a 4-fold decrease in E-modulus in osteoporotic bone. Finite element analysis (FEA) was employed to examine the impact of screw size and bone quality on stability, measuring loads at a 5.4 mm displacement threshold, a key parameter for loosening. Results demonstrated that cortical thickness had a greater influence on screw stability than biomechanical properties and increasing screw diameter improved stability more effectively than increasing screw length, particularly in osteoporotic bone. Subcortical bone properties contributed minimally. Validation against existing literature supports the conclusion that effective pedicle screw anchoring requires adequate cortical bone and quality in the pedicle region. Future research should refine subcortical bone properties in models and incorporate morphological changes from aging to improve simulation accuracy.
Keywords: pedicle screw; posterior fixation system; vertebral fractures; pedicle screw loosening; pedicle-screw-rod construct; finite element analysis (FEA); cortical bone; subcortical bone; cancellous bone; lumbar spine; healthy vertebral model; osteoporotic vertebral model; osteoporosis; pedicle screw stability; lumbar spine; pedicle screw strength; spondylodesis; morphometric vertebral bone properties
 
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