Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch |
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Authors: | Matthias Gebauer Florian Barvencik Daniel Briem Jan P Kolb Sebastian Seitz Johannes M Rueger Klaus Püschel Michael Amling |
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Institution: | (1) Department of Trauma-, Hand-, and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany;(2) Department of Experimental Trauma Surgery and Skeletal Biology, Center for Biomechanics, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany;(3) Department of Forensic Medicine, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany |
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Abstract: | Several studies have evaluated quantitative anatomic data for direct lateral mass screw fixation. To analyze anatomic landmarks and safe zones for optimal screw placement through the posterior arc of the
human atlas, morphometric parameters of 41 adult native human atlas specimens were quantitatively measured. Internal dimensions
of the atlas (lateral mass, maximum and minimum intraosseous screw length), minimum height and width of the posterior arc
and optimal screw insertion angles were defined on pQCT scans. By this, an optimal posterior screw insertion point (OIP) and
a preferable screw direction (PSD) through the posterior arch into the lateral mass of C1 were defined. External dimensions
(transverse and sagittal diameter) as well as the width of the mid-portion of C1 lateral mass were significantly higher in
male specimens. The mean height of the posterior arch at the vertebral artery groove was 4.1 ± 0.8 mm in female and 4.6 ± 0.9 mm
in male specimens. The optimal screw insertion point was located 21.6 ± 1.7 mm in female and 23.6 ± 2.3 mm in male lateral
from the posterior tubercle of C1 (P < 0.01). The preferable screw direction was a mean medial inclination of 7.9 ± 1.9° in female and 7.3 ± 2.7° in male specimens
and a mean rostral direction of 2.4 ± 1.8° in female and 3.1 ± 1.7° in male specimens. In conclusion, the presented study
provides information for the use and design of upper cervical spine instrumentation techniques, such as screw placement to
C1 via the posterior arch. The characterization of working areas and safe zones (OIP, PSD) might contribute to a minimization
of screw malposition in this highly demanding instrumentation technique. |
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Keywords: | Atlas Posterior screw placement Transpedicular Lateral mass |
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