The optimal transarticular C1-2 screw length and the location of the hypoglossal nerve

BACKGROUND Injury to the hypoglossal nerve is a complication associated with transarti cular C1-2 screw placement. This complication can be caused by a misdirecte d or too long screw. Little is known about the optimal screw length and its relationship to the hypoglossal nerve. METHODS Twenty cervical spine specimens were used to study the optimal length of th e transarticular C1-2 screw. Using the Magerl technique, a 3.0 mm drill bit was inserted into the C2 lateral mass, passing through the C1-2 facet join t and penetrating the upper portion of the ventral cortex of the lateral ma ss of the atlas. After drilling, the hole length was measured between the d orsal cortex of the C2 inferior articular process and the ventral cortex of the C1 lateral mass. In addition, six sagittal-sectioned cadavers were car efully dissected to observe the location of the hypoglossal nerve in the an terior aspect of the atlantoaxial region. RESULTS The results of the measurements showed that the mean optimal screw path len gth for all specimens was 38.1 +/- 2.2 mm with a range of 34-43 mm. There w as no significant difference between sexes in the screw path length (p > 0. 05). The hypoglossal nerve lies vertically in front of the lateral portion of the C1 lateral mass and the C1-2 facet joint. The area where the hypoglo ssal nerve lies is approximately 2-3 mm lateral to the middle of the anteri or aspect of the C1 lateral mass. CONCLUSIONS This study suggests that the mean optimal transarticular C1-2 screw length may be 38 mm; however, the determination of the accurate optimal C1-2 screw length should be made on an individual basis. Risk to the hypoglossal nerv e can be eliminated if Magerl's technique is performed exactly. (C) 2000 by Elsevier Science Inc.