• Xiang-Yang Ma, Qing-Shui Yin, Zeng-Hui Wu, Hong Xia, K Daniel Riew, and Jing-Fa Liu.
• From the *Department of Orthopedics, Guangzhou Liu Hua Qiao Hospital, Guangzhou, People's Republic of China; and †Department of Orthopedics, Washington University School of Medicine, St. Louis, MO.
• Spine. 2010 Mar 15; 35 (6): 704708704-8.

Study DesignA cadaveric specimen study.ObjectivesTo determine the applicability of a modified C2 translaminar screw placement in the general adult population and to provide pertinent clinical data for screw insertion.Summary Of Background DataC2 intralaminar screw fixation has recently been popularized, but this technique carries a potential drawback that the screw may breakout ventrally into the spinal canal. For this reason, a modified C2 translaminar screw fixation technique was developed to intraoperatively verify screw position and thereby decrease the risk or canal compromise. To our knowledge, there has been not an anatomic study evaluating this modification of the translaminar screw technique.MethodsThe tips of the modified screws were aimed such that they exited the dorsal cortex of the center of the contralateral lateral mass, achieving bicortical fixation. A total of 120 adult C2 vertebrae were evaluated bilaterally for the following: thickness of the cranial, midportion, and caudal edge of C2 lamina; the heights of the spinous process, lamina, and lateral mass; inclination angle of the laminae, screw projection length, and trajectory angle of cranial and caudal C2 translaminar screw.ResultsA total of 83.3% specimens had bilateral laminar thicknesses ≥4.0 mm and a spinous process height ≥9.0 mm; 5% had a laminar thickness less than 4.0-mm bilaterally; 9.2% had a laminar thickness less than 4.0 mm on one side; 2.5% had a spinous process height lower than 9.0 mm.ConclusionA large percentages of C2 laminae are of sufficient size to safely accommodate a bicortical 3.5-mm diameter screw. The thickness of the lamina and the height of the spinous process are the 2 limiting factors for safe translaminar screws placement. Using a bicortical technique confirms the position of the screw and thereby helps to decrease the risk of neurologic injury from screw penetration of the inner cortex of the lamina.

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