Related Experiment Video
Updated: Aug 15, 2026
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 biomechanical study of anterior thoracolumbar screw fixation
S W Breeze1, B J Doherty, P S Noble
1Department of Orthopedic Surgery, Institute for Spinal Disorders, Baylor College of Medicine, Houston, Texas, USA.
Study Design:
The pullout strength of unicortical and bicortical screws in thoracic and lumbar vertebral bodies was measured as a function of bone mineral density.
Objectives:
To determine the influence of bone mineral density and screw insertion technique on the stability of anterior thoracolumbar spine screw fixation.
Summary Of Background Data:
No previous study has addressed the specific technique of screw insertion or stability of screw fixation in the anterior spine.
Methods:
Fifty-one human thoracic vertebral bodies were tested in pullout with 6.55-mm cancellous screws inserted using unicortical and bicortical techniques.
Results:
Pullout force increased exponentially with increasing bone mineral density for unicortical and bicortical screws. Bicortical screws were significantly stronger in resisting pullout than unicortical screws.
Conclusion:
Advancing an anterior vertebral body screw to engage the second cortex increases resistance to pullout by 25-44%, depending on vertebral bone mineral density. The difference in resistance between unicortical and bicortical techniques was smaller in specimens with low mineral densities.
