An anatomic study to determine the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws.
METHODS
Anatomic study of the C1 lateral mass using fine-cut computed tomographic scans and Mimics software.


OBJECTIVE
To investigate the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws.


BACKGROUND
Placing posterior C1 lateral mass screws is technically demanding, and a misplaced screw can result in injury to the vertebral artery, spinal cord, or internal carotid artery. Although various insertion angles have been proposed for posterior C1 lateral mass screw, no clear consensus has been reached on the ideal medial angle of the C1 lateral mass.


METHODS
The C1 lateral masses were evaluated using computed tomographic scans and Mimics software in 70 patients. The effective width and effective screw length of posterior C1 lateral mass screws were measured at different medial angulations relative to the midline sagittal plane. The height (H) for screw entry point on the posterior surface of C1 lateral mass and the distance (D) between screw entry point and the intersection of the midline sagittal plane and the posterior arch of the atlas were also measured.


RESULTS
The mean height (H) for screw entry on the posterior surface of the lateral mass was 4.25 mm, the mean distance (D) between screw entry point and the intersection of the midsagittal plane and the posterior arch of the atlas was 27.62 mm. The optimal medial angle was 20.86° with a corresponding effective width of 10.56 mm and effective screw length of 21.87 mm.


CONCLUSIONS
This study helps to define the specific anatomy related to C1 posterior lateral mass screw placement in an effort to facilitate instrumentation. However, variation is seen in lateral mass anatomy, and this study must be combined with customized surgical planning that includes advanced imaging for safe and effective instrumentation.


METHODS
1.
*Department of Spinal Surgery, Ningbo No. 6 Hospital, Ningbo, Zhejiang Province, China †Department of Orthopaedic Surgery, University of Utah, Salt Lake City, UT; and ‡Department of Orthopaedic Surgery, Thomas Jefferson University & Rothman Institute, Philadelphia, PA.
Yong
Y
Hu
Wei-xin
WX
Dong
William Ryan
WR
Spiker
Zhen-shan
ZS
Yuan
Xiao-yang
XY
Sun
Jiao
J
Zhang
Hui
H
Xie
Todd J
TJ
Albert
D000293:Adolescent; D000328:Adult; D001268:Atlanto-Axial Joint / Q000601:surgery*; D001863:Bone Screws; D001270:Cervical Atlas / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019547:Neck Pain / Q000601:surgery; D013123:Spinal Fusion / Q000379:methods*; D055815:Young Adult