Surgical anatomic evaluation of the cervical pedicle and adjacent neural structures

OBJECTIVE: Although several clinical applications of transpedicular screw f ixation in the cervical spine have been documented recently, few anatomic s tudies concerning the cervical pedicle are available. This study was design ed to evaluate the anatomy and adjacent neural relationships of the middle and lower cervical pedicle (C3-C7). The main objective is to provide accura te information for transpedicular screw fixation in the cervical region and to minimize complications by providing a three-dimensional orientation. METHODS: Twenty cadavers were used to observe the cervical pedicle and its relationships, After removal of the posterior bony elements, including spin ous processes, laminae, lateral masses, and inferior and superior facets, t he isthmus of the pedicle was exposed. Pedicle width, pedicle height, inter pedicular distance, pedicle-inferior nerve root distance, pedicle-superior nerve root distance, pedicle-dural sac distance, medial pedicle-dural sac d istance, mean angle of the pedicle, root exit angle, and nerve root diamete r were measured. RESULTS: The results indicate that there was no distance between the pedicl e and the superior nerve root and between the pedicle and the dural sac in 16 specimens, whereas there was a slight distance in the lower cervical reg ion in the 4 other specimens. The mean distance between the pedicle and the inferior nerve root for all specimens ranged from 1.0 to 2.5 mm. The mean distance between the medial pedicle and the dural sac increased consistentl y from 2.4 to 3.1 mm. At C3-C7, the mean pedicle height ranged from 5.2 to 8.5 mm, and the mean pedicle width ranged from 3.7 to 6.5 mm. Interpedicula r distance ranged from 21.2 to 23.2 mm. The mean root exit angle ranged fro m 69 to 104 degrees, with the largest angle at C3 and the smallest at C6. T he mean angle of the pedicle ranged from 38 to 48 degrees. The nerve root d iameter increased consistently from 2.7 mm at C3 to 3.8 mm at C6 and then d ecreased to 3.7 mm at the C7 level. Differences in measurements were consid ered statistically significant at levels ranging from P < 0.05 to P < 0.01. CONCLUSION: This study indicates that improper placement of the pedicle scr ew medially and superiorly in the middle and lower cervical spine should be avoided and that the anatomic variations between individuals should be est ablished by measurement.