C1–C2 Trauma Injuries and Stabilization Techniques

Overview

Fractures of the atlas and axis are often seen in the setting of trauma to the craniocervical junction (CCJ). Injuries to these vertebrae can induce instability and result in devastating neurologic injury. Atlantoaxial instability is present once the transverse ligament has been disrupted, the odontoid process has been fractured, or both. Unless the transverse ligament is avulsed with its bony base, the chance of healing is slim with external immobilization alone. Therefore, internal fixation is often necessary to treat such instability. Depending on the type of odontoid fracture, surgical fixation may be indicated to achieve fusion. Atlantoaxial instability can also result from vertical distraction that damages the atlantoaxial joint and capsule. If the injury is severe, internal fixation and fusion may be necessary. This chapter describes operative techniques used to fixate and fuse traumatic injuries of the atlas and axis.

General Operative Techniques for Posterior Atlantoaxial Fixation

The patient is log-rolled into a prone position. Somatosensory evoked potentials (SSEPs) can be monitored to achieve safe positioning. When present, the halo ring is attached to the Jackson table. After the suboccipital portion of the head is shaved, the CCJ area is prepared and draped in a sterile fashion. The skin over the iliac crest on either side is also prepared in case an autologous graft becomes necessary.

After positioning and before the surgery begins, a fluoroscopic image should be obtained to verify that cervical alignment is maintained. The intent is to place the patient in a neutral head position, if possible. Next, an incision is made from the external occipital protuberance to C4–C5. The lower extent of the incision depends on the patient’s local anatomy, thickness of the neck, redundancy of tissues, and the desired level of fusion or fixation. After the skin has been incised, dissection proceeds to the spinous process of C2–C3, or further if necessary.

Subperiosteal dissection is performed using monopolar cauterization. Because this segment is very unstable, periosteal elevators should be applied with care. Too much pressure exerted on the posterior bony elements can cause motion at the subluxed level.

After the spinous process, lamina, and posterior arch of C1 are exposed, gentle dissection continues laterally over the facet joints of C2–C3 and C3–C4 and, if necessary, over those at other levels. Injury to the vertebral artery should be avoided, especially at the C1–C2 complex and overlying the arterial sulcus of C1. At this point, gentle subperiosteal dissection and bipolar cauterization are preferred over monopolar cauterization. If brisk venous bleeding is encountered, it is usually a warning sign that the vertebral artery is near. After the bony structures are exposed, several methods of fixation are possible.

C1–C2 Lateral Mass–Pars Interarticularis Screw Fixation

If screw fixation of the atlantoaxial junction is desired, screws can be placed in the lateral mass of C1 and in the pars interarticularis of C2. If necessary, screws can be placed into the lateral masses on the subaxial spine; this technique is reviewed elsewhere in this text. This section reviews placement of screws into the C1 lateral mass and pars interarticularis of C2.

After the C1 posterior arch is exposed completely, an air drill is used to drill the pilot hole for the screw within the underside of the lamina of C1, where it joins the C1 lateral mass ( Fig. 12-1, A ). A drill is used to make a pilot hole in the C1 lateral mass under fluoroscopic guidance; the lateral mass screw should have a slight medial and superior angulation (fewer than 10 degrees, see Fig. 12-1, B and C ). Care is taken to avoid injuring the vertebral artery. A number 4 Penfield dissector is inserted along the medial aspect of the C1 lateral mass to delineate its medial border.

Under direct lateral fluoroscopic visualization of the medial border, the sagittal angle is identified. Unicortical purchase is desired. Bicortical purchase can injure structures anterior to the spine and should not be attempted. At this point, the length of the screw is measured; the diameter of the screw depends on the local anatomy. Again, the medial border of the occiput of the C1 junction is palpated with a number 4 Penfield dissector to ensure that the cortex is not violated.

Next, the venous plexus around the medial and superior side of the C2 pars interarticularis is cauterized with the bipolar device, cut with microscissors, and compressed with Nu-Knit (Johnson & Johnson, Arlington, TX) or Gelfoam (Upjohn, Kalamazoo, MI) and cottonoids. A pilot hole is drilled in the inferior side of the lateral mass of C2 at the midportion of the C2–C3 facet joint and into the C2 pars interarticularis, which has been exposed to the junction of the C1–C2 articulation. To visualize the trajectory of the screw, the C2 nerve root is retracted rostrally with a number 4 Penfield dissector. A 10- to 15-degree medial angulation is used for the pars interarticularis screw ( Fig. 12-2, A ); the sagittal trajectory misses the C1–C2 joint (see Fig. 12-2, B ). Lateral fluoroscopy is also used to guide the drilling. Usually, the C2 pars interarticularis screw is short and measures less than 12 mm.

C1–C2 Lateral Mass–Pedicle Screw Fixation

The exposure is the same as that used for the C2 pars screw. The landmark for the insertion of the C2 pedicle screw is the cranial margin of the C2 lamina ( Fig. 12-3 ). Using a high-speed drill, the insertion site is demarcated. A Penfield instrument can be used to identify the superomedial surface of the C2 pedicle by placing it into the interlaminar space along the top margin of the C2 lamina. The angle of insertion of the pedicle screw should be 15 to 25 degrees medial to the midline in the transverse plane. Next, the hole is drilled and tapped. A ball-tip probe is used to confirm patency of the screw canal. Screws as long as 24 mm (20 to 24 mm) may be used in the C2 pedicle.

Atlantoaxial Transarticular Fixation

After the path is tapped, the screw is inserted. If a C1–C2 transarticular screw is required, the screw is angled toward the anterior tubercle of C1 using a slightly more medial pilot hole than that used for the C2 pars interarticularis screw ( Fig. 12-4, A ). However, there is almost no medial angulation of the screw, and the trajectory is straight up into the C1 lateral mass (see Fig. 12-4, B ). The pars interarticularis of C1 and the C1–C2 articulation are dissected as described for placement of a C2 pars interarticularis screw. The length, which is usually about 40 mm, is again measured using the K-wire method. If a lag effect is desired, an end-threaded screw can be used instead of a fully threaded screw.