J Korean Neurosurg Soc.  2013 Jul;54(1):25-29. 10.3340/jkns.2013.54.1.25.

Anatomic Consideration of the C1 Laminar Arch for Lateral Mass Screw Fixation via C1 Lateral Lamina : A Landmark between the Lateral and Posterior Lamina of the C1

• Kim JH
• Kwak DS
• Han SH
• Cho SM
• You SH
• Kim MK

• KMID: 2190853
• DOI: http://doi.org/10.3340/jkns.2013.54.1.25

Abstract

OBJECTIVE
To clarify the landmark for deciding the entry point for C1 lateral mass screws via the posterior arch by using 3-dimensional (3D) computed images.
METHODS
Resnick insisted that the C1 posterior arch could be divided into pure posterior and lateral lamina (C1 pedicle). Authors studied where this transition point (TP) is located between the posterior lamina and the C1 pedicle and how it can be recognized. The 3D computed images of 86 cadaver C1s (M : F=45 : 41) were used in this study.
RESULTS
The superior ridge of the C1 posterior arch had 2 types of orientation. One was in the vertical direction in the C1 posterior lamina and the other was in the horizontal direction in the C1 pedicle. The TP was located at the border between the 2 areas, the same site as the posterior end of the groove of the vertebral artery. On posterior-anterior projection, the posterior arch was sharpened abruptly at TP. We were unable to identify the TP in 6.4% of specimens due to complete or partial osseous bridges. A total of 93.8% of the TP were located between the most enlarged point of the spinal canal and the medial wall of the vertebral artery.
CONCLUSION
The anatomic entry zone of C1 lateral laminar screws was clarified and identified based on the TP by using preoperative 3D computed images.

Keyword

Lateral mass screw; Atlas; Lamina; Entry point; Landmark; Preoperative computed tomography

MeSH Terms

Cadaver
Spinal Canal
Vertebral Artery

Figure

• 

  Fig. 1 Definition of the transition point (TP). A : The posterior end (asterisk) of the groove of the vertebral artery can be seen in the posterior view from slightly above the lamina by 10-15°. B : The same site (arrow head) is denoted in the superior view of the atlas. C-F : Images are posterior views of C1 in various angles (C : +30°, D : +15°, E : 0°, F : -30°, asterisk : TP).

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  Fig. 2 Two orthogonal views (A : top; B : posterior side) of an atlas. H : minimal height of the C1 lateral lamina (C1 pedicle), Lt/Rt : left and right, M : maximal spinal canal diameter from midline, T : distance from midline to TP, VH : distance from midline to the medial side of the transverse foramen outlet, VL : distance from midline to the medial side of the transverse foramen inlet.

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  Fig. 3 Relative laterality ratio of a TP. This shows where a transition point is located comparing the safety zone between the spinal canal and the transverse foramen. Ratio=T/(VL - M). TP : transition point, VL : distance from midline to the medial side of the transverse foramen inlet, T : distance from midline to TP, M : maximal spinal canal diameter from midline.

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  Fig. 4 Lateral margin of the atlanto-occipital membrane (arrow heads).

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  Fig. 5 Distribution of TPs. Individual dots show the relative laterality ratio of TP. X-axis : the relative laterality ratio, Y-axis : cadaver number, TP : transition point.

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