Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 39. Spinal disorders are among the most common medical conditions with significant impact on health related quality of life, use of health care resources and socio-economic costs. Spinal surgery is still one of the fastest growing areas in clinical medicine. | 362 Section Surgical Approaches a Posterior view. b Axial view. Figure 14. Landmarks for occipital screw insertion Injuries to the spinal cord or vertebral artery are rare if the technique is applied The 2nd cervical nerve is at risk when exposing the C1 2 joint nar control for optimal screw placement. The medial border of the C2 pedicle 2-5 mm axial diameter should be palpated with a dissector or a nerve hook. The screw is positioned as medially as possible to avoid injuries to the vertebral artery which lies immediately laterally. The entry point for screw insertion is about 3 mm cranial to the lower edge of the C2 inferior facet. Usually there is a small groove at the transition of the inferior facet to the lamina which serves as a landmark for the entry point. The drill is angled to aim at the arch of C1 in a strictly sagittal plane. The screw should pass just below the posterior border of the C1 2 joint. In some cases the craniocaudal angulation can only be achieved if the drill is significantly inclined. Rather than dissecting all the posterior muscles we prefer only to expose the spine from C1 to C3 and choose a percutaneous insertion of the drill usually at the level of C7-T1 with a tissue protector. Injuries to the vertebral artery or spinal cord are rare if the technique is performed properly 22 27 . Atlantoaxial Pedicle Screw Fixation An alternative to the transarticular screw fixation is a stabilization of the spine with pedicle screws which are connected with rods 29 64 Fig. 15d-g . The screw entry point in C2 is more lateral 4-5 mm than the transarticular screw trajectory. The drill is directed 20 -35 cranially and 15 -20 medially. The entry point in Cl is below the lamina and 2-3 mm lateral to the medial edge of the C1 which can be palpated with a dissector. The screw is aimed about 10 -15 medially and 15 -20 cranially. Care has to be taken not to injure the C2 exiting nerve root greater occipital nerve . Anterior Atlantoaxial Transarticular Screw .
