Fixation strength of unicortical versus bicortical C1–C2 transarticular screws

Abstract Background context The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1–C2 transarticular screws. This has led to the recommendation for unicortical screws if the neurovascular structures are in cl...

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Bibliographic Details
Published in:The spine journal 2008-07, Vol.8 (4), p.661-665
Main Authors: Cyr, Steven J., MD, Currier, Bradford L., MD, Eck, Jason C., DO, MS, Foy, Andrew, MD, Chen, Qingshan, MS, Larson, Dirk R., MS, Yaszemski, Michael J., MD, PhD, An, Kai-Nan, PhD
Format: Article
Language:English
Subjects:
Atlantoaxial
Biomechanics
Bone Screws
C1–C2 transarticular screw fixation
Cadaver
Cervical spine
Cervical Vertebrae - surgery
Equipment Design
Equipment Failure Analysis
Fixation
Humans
Materials Testing
Orthopedics
Shear Strength
Spinal Fusion - instrumentation
Stress, Mechanical
Transarticular screw
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Summary:Abstract Background context The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1–C2 transarticular screws. This has led to the recommendation for unicortical screws if the neurovascular structures are in close proximity to the proposed exit point. No data are available on strength of unicortical versus bicortical C1–C2 transarticular screws. Purpose To compare the biomechanical pullout strength of unicortical versus bicortical C1–C2 transarticular screws in a cadaveric model. Study design Biomechanical study. Methods Fifteen cervical spine specimens underwent axial pullout testing. A unicortical C1–C2 transarticular screw was placed on one side with a contralateral bicortical screw. Data were analyzed to reveal any significant differences in strength. Results Mean pullout strength for the bicortical C1–C2 transarticular screws was 1,048.8 (±360.1) N versus 939.2 (±360.6) for unicortical screws (p=.22). There was no significant difference in the pullout strength of unicortical and bicortical screws. Conclusions In cases with satisfactory bone quality, it appears reasonable to use unicortical screws to avoid the risk of neurovascular injury from penetrating the anterior cortex of C1.
ISSN:1529-9430
1878-1632
DOI:10.1016/j.spinee.2007.02.008