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Updated: Apr 26, 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
Pullout strength of thoracic pedicle screws improved with cortical bone ratio: a cadaveric study
Wen-Kai Chou1, Andy Chien, Jaw-Lin Wang
1Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, 602 Jen-Shu Tower, 1, Section 4, Roosevelt Road, Taipei, 10617, Taiwan, ROC.
Background:
The application of pedicle screw constructs for the osteoporotic vertebrae remains a serious clinical challenge for spinal surgeons and has been intensely studied recently. However, the exact role of the pedicular cortical bone composition and the screw-bone gap on the screw fixation failure has yet to be quantitatively documented. The current study aims to address this gap in our knowledge and elucidate possible relationships.
Methods:
Twelve fresh-frozen human cadaveric thoracic spine vertebrae (T9-T12) were harvested from six human cadavers (five males; one female; 63.5 ± 17 years). A three-dimensional reconstruction of the individual vertebrae was firstly rendered from computed tomography (CT) scan images to allow calculation of the cortical bone ratio. Specimens were then subdivided into three groups: Intact, 1-mm screw-bone gap, and 2-mm screw-bone gap. The gap groups were subjected to a standard cyclic fatigue-loading protocol. The pullout strength of the pedicle screws for all specimens were then determined.
Results:
The pullout strength of the 1-mm and 2-mm groups were significantly reduced when compared with the intact group. A moderate to excellent positive correlation was identified between the cortical bone area ratio and pullout strength for all groups (r > 0.55). A cortical shell ratio of 0.73 or higher was also found to be a safe cut-off index for screw fixation failure, even with an observable 1-mm screw-bone gap.
Conclusions:
The current in vitro cadaveric spine study identified a significant correlation between cortical bone area ratio and the thoracic pedicle screw pullout strength. The presented results also demonstrate that the fatigue-loading-induced screw-bone gap of 1-mm was sufficient to cause a significant decrease in the pullout strength. However, a cortical bone area ratio of 0.73 or higher in this group was able to preserve most of the screw-bone interfacial strength, and subsequently may prevent a complete implant failure.
