Anatomic relationship of the cervical nerves to the lateral masses.

Eight cervical specimens were transversely sectioned with slices approximately 2 mm to 3 mm in thickness to evaluate the anatomic relationship of the spinal nerves to the lateral masses. Results showed that the spinal nerve either does not appear or, when it does, is situated anteromedially to the superior facet on the cross sections through the upper portion of the superior facet. The anterolateral aspect of the superior facet is free from the spinal nerve. Cross sections through the lower pedicle of the vertebra showed that the spinal nerve rested on the transverse process anterolateral to the lateral mass. The mean distances between the posterior midline of the lateral mass and the posterior border of the spinal nerve measured 15 degrees in the lateral direction were 16.1+/-1.7 mm for C3, 16.5+/-1.8 mm for CA, 16.8+/-1.2 mm for C5, 16.3+/-2.0 mm for C6, and 8.5+/-0.9 mm for C7. This study suggests that the anterolateral corner of the superior facet and the anterior aspect of the lateral mass lateral to the origin of the transverse process would be safer zones for screw exit. Attention should therefore be paid to the screw orientation for the Magerl technique and to the screw length for the Roy-Camille technique. Care should be taken to insert the screw into the C7 lateral mass.