C1-C2 Transarticular Screws

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Chapter Synopsis	Placement of the C1-C2 transarticular screw (Magerl technique) remains a viable alternative for the surgical management of a variety of atlantoaxial disorders. Although the operation is technically demanding, a careful understanding of the procedure and its limitations, as well as a thorough understanding of each patient’s individualized bony and vascular anatomy, can help reduce the risk of complications. Proper preoperative radiographic evaluation including x-ray studies, computed tomography (CT), and CT angiography or magnetic resonance angiography is necessary. When used in the appropriate patient, the Magerl technique yields excellent results with high fusion rates and relatively low complication rates. The purpose of this chapter is to review the indications for surgery, the surgical technique, and the relative advantages and disadvantages of C1-C2 transarticular screw fixation.
Important Points	Indications for C1-C2 transarticular screw fixation include acute or chronic atlantoaxial instability in patients in whom conservative treatment has failed. Biomechanically, transarticular fixation provides superior biomechanical stabilization compared with other C1-C2 fixation techniques, particularly in axial rotation and lateral bending. Advanced imaging, including multiplanar reformatted CT scan, should be reviewed to determine whether screw placement is feasible and safe. Attention should be paid to the course and caliber of the vertebral artery, particularly around the C1-C2 joint and the C2 isthmus.
Clinical and Surgical Pearls	Adequate fluoroscopy should be ensured with the technologist after positioning of the patient. The Mayfield clamp should be adjusted to ensure proper positioning, including rotation. Reduction of C1-C2 before drilling must be obtained. A rigid drill guide tube should be used. Fluoroscopy should be used through each stage of the procedure, and the surgeon should be mindful of inadvertent Kirschner wire migration when using cannulated screw systems.
Clinical and Surgical Pitfalls	Lack of understanding of the patient’s bony and vascular anatomy can lead to complications including bleeding, stroke, or neurologic injury (hypoglossal nerve). Improper positioning and inadequate preparing or draping of the upper thoracic area make the tunneling of instruments at the appropriate trajectory difficult. Failure to obtain adequate visualization of the C2-C3 facet joint and the mediolateral extent of the C2 isthmus may make placement of the C1-C2 transarticular screw difficult. The greater danger in using this technique is vertebral artery injury. The risk of spinal cord injury is extremely low. The drill trajectory should therefore “hug” the medial aspect of the isthmus as much as possible to avoid inadvertently entering the foramen transversarium.

The preferred method for C1-C2 posterior fixation by many spine surgeons has become the C1 lateral mass, C2 pars, or pedicle screw and rod construct (Harms-Goel) discussed in the previous chapter. Although several factors have led to that method’s increasing popularity, surgeons’ familiarity with screw-based instrumentation systems ubiquitously used in the subaxial cervical spine has likely played a significant role. Despite being used less frequently than in years past, the C1-C2 transarticular technique originally described by Magerl offers some unique advantages over other atlantoaxial stabilization methods, and some experts consider it the gold-standard for posterior fixation in the treatment of atlantoaxial instability. Regardless, every practicing spine surgeon should gain an understanding of the surgical technique and associated anatomy for placement of the C1-C2 transarticular screw.

The method employs the posterior placement of screws through each pars interarticularis (isthmus) of C2 directly across the C1-C2 facet joint into the C1 lateral mass. This technique provides excellent fixation in all degrees of freedom, particularly axial rotation and lateral bending. When this technique is combined with an interspinous graft and cable construct such as the Sonntag modification of the Gallie fusion, biomechanical strength is further increased, and postoperative halo immobilization is not required ( Fig. 40-1 ). The resulting construct was shown to be superior to other C1-C2 stabilization techniques in published biomechanical studies.

The technique for transarticular screw placement can be technically demanding, and it requires the spine surgeon to have familiarity with the procedure and its limitations, as well as an excellent understanding of the individual patient’s bony and vascular anatomy. Proper preoperative radiographic evaluation including x-ray studies, computed tomography (CT), and CT angiography or magnetic resonance angiography (MRA) is necessary. When used in the appropriate patient, the Magerl technique yields excellent results, with high fusion rates (96%) and relatively low complication rates (8%).

Indications and Contraindications

Transarticular fixation is indicated for acute or chronic atlantoaxial instability, whether it be caused by trauma, inflammatory disease, infection, congenital disease, or iatrogenic destabilization ( Box 40-1 ). The technique can be combined with occipital or subaxial fixation, or both, if necessary ( Fig. 40-2 ).

BOX 40-1

Indications for Transarticular Screw Fixation

Trauma

Jefferson fractures (C1 burst) with transverse ligament disruption unstable odontoid fractures: type II and shallow type III unstable hangman’s fractures

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