C2 Translaminar Screw Fixation

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Chapter Synopsis	C2 translaminar screws are an effective method for fixation of the C2 vertebra. Compared with other techniques, this procedure is technically less demanding and has potentially fewer risks. A thorough history and examination, as well as a careful assessment of the anatomy of the C2 lamina, are still required preoperatively to minimize complications. The goal of this chapter is to review preoperative considerations, surgical technique, and results for C2 translaminar screw fixation.
Important Points	The patient’s C2 laminar anatomy must demonstrate the ability to accommodate a screw. Unlike other C2 fixation techniques, the translaminar screw does not place the vertebral arteries at risk. A history of previous surgical procedures or of congenital cervical spinal abnormalities may be an absolute or relative contraindication to the placement of translaminar screws.
Clinical and Surgical Pearls	The translaminar screw starting point is typically at the junction of the spinous process and the lamina. The first screw should be placed as close to the superior margin of the C2 lamina as possible. The second screw can be placed at the inferior portion of the lamina to prevent interference with the previously placed contralateral translaminar screw. Decortication of the C2 lamina does not affect the stability of the translaminar screw.
Clinical and Surgical Pitfalls	Congenital abnormalities may have other associated disorders, such as occipitalization or absent posterior elements, that may preclude or alter the surgical decision-making process. Laminae less than 3.5-mm thick may be at risk for anterior or posterior screw penetration. During placement of the screw, the alignment of the drill can be kept slightly posterior to ensure that any potential cortical violation would occur posteriorly through the surface of the lamina rather than anteriorly into the spinal canal.

Bilateral crossing C2 translaminar screws can be an attractive option when contemplating fixation of the C2 vertebra (axis). The procedure is not technically demanding and provides rigid fixation. Traditional posterior wiring methods are also technically simple, but they are associated with suboptimal fusion rates resulting from limited stiffness. Translaminar screws are not as affected by variations in a patient’s anatomy and do not risk injury to the vertebral arteries, unlike other technically demanding C2 screw fixation options (C1-C2 transarticular screws, C2 pedicle screws).

In an attempt to reduce the risk of injury to the vertebral artery during placement of the C2 pedicle screw, the C2 pars interarticularis fixation, which uses a shorter screw (14 to 16 mm) and a slightly different trajectory, has been suggested to be less risky to the vertebral arteries than longer pedicle screw placement. However, the biomechanical strength of the C2 pars screw has not been proven, and anatomic variations may also prevent placement of this screw. Therefore, developing an understanding of the anatomy and technique for placement of C2 translaminar screw fixation can provide an additional method for rigid fixation of the axis that may be incorporated with occipitoatlantal or subaxial instrumentation. The goal of this chapter is to review preoperative considerations, surgical technique, and results for the placement of C2 translaminar screw fixation.

Preoperative Considerations

The indications for surgery and the use of translaminar screws for stabilization of disorders of the cervical spine remain the same as for other cervical procedures. Although described more completely in other chapters, patients with myelopathy, radiculopathy, myeloradiculopathy, tumors, infection, or trauma with associated cervical instability are potential candidates.

The history and examination should include evaluation for standard signs and symptoms of myelopathy or radiculopathy. Motor weakness, sensory deficits, and reflex changes can help identify the disorder. In addition to the standard history and examination, particular attention should also include evidence of previous posterior cervical spinal surgical procedures or congenital abnormalities that may have resulted in the resection or absence of the C2 lamina, which could preclude the use of translaminar screws. In addition, a search for subtle examination findings such as a low-lying hairline, webbed neck, and decreased range of motion can identify abnormalities such as Klippel-Feil syndrome. This syndrome is associated with congenitally fused cervical segments and frequently with occipitalization, and it may alter the surgical technique selected.

Imaging studies should start with plain radiographs and include cervical spine anteroposterior, lateral, and flexion and extension dynamic imaging studies to assess overall alignment, degenerative disease, osteophytes, range of motion, and stability.

Advanced imaging, in the form of magnetic resonance imaging (MRI), can provide information about the intervertebral disks, cranial and spinal nerve roots, supporting ligaments, presence of a syrinx, Chiari malformation, and information on the spinal cord caliber and quality, among other things. Although MRI is typically the imaging study of choice for identifying disease, the addition of a computed tomography (CT) scan, with or without a myelogram, can be particularly useful when deciding to place translaminar screws.

The CT scan can help provide additional information about the presence and extent of the bony compression, presence of ossification of the posterior longitudinal ligament (OPLL), and in revision cases, presence of a solid fusion or pseudarthrosis. More specifically, with regard to translaminar screws, preoperative CT imaging of the cervical spine is important to ensure that a patient’s anatomy can accommodate a screw (length and width) before screw placement is attempted ( Fig. 41-1 ).

Indications and Contraindications

Indications

Traumatic fracture, traumatic ligamentous laxity, rheumatoid arthritis, congenital disorders, neoplasm, pseudarthrosis, degenerative disease, C1-C2 subluxation, os odontoideum, type II odontoid process fracture, and unfavorable anatomy for C2 transarticular screw or pedicle screw placement are frequent indications for consideration of placement of C2 translaminar screws.

Contraindications

This procedure is contraindicated in patients with earlier C2 laminectomy, C2 posterior element fracture, C2 lamina that is less than 3.5-mm thick, and congenital and anatomic variants with absent or dysplastic C2 lamina. In addition, an anomalous vertebral artery that places its course within the trajectory of the C2 translaminar screw is also a contraindication to placement of a screw, at least on the side of the anomalous anatomy.

Surgical Technique

Anesthesia and Positioning

After induction of general anesthesia and setup of intraoperative neuromonitoring, a Mayfield (Integra, Plainsboro, NJ) three-pin skull clamp is placed, and the patient is placed in the prone position on a Jackson table (Mizuho OSI, Union City, Calif.) with the head and cervical spine in neutral position. The Mayfield clamp is then secured to the C-Flex head positioning system (Allen Medical Systems, Acton, Mass.) and is adjusted as needed for final alignment.

Surgical Steps

A posterior midline incision is made, and subperiosteal dissection of the C1 (axis) posterior arch and the other adjacent areas to be instrumented (subocciput, atlas, or subaxial spine) is carried out in the usual fashion ( Box 41-1 ). If included in the construct, the posterior arch of C1 is dissected to expose the lateral masses bilaterally. The spinous process, laminae, and medial aspect of the lateral masses of C2 are exposed. The spinous process, laminae, and lateral masses are then exposed as needed for the subaxial vertebrae to be included in the construct.

BOX 41-1

1.

Use of a high-speed drill to open a small cortical window at the junction of the C2 spinous process and lamina on the right, close to the superior margin of the C2 lamina ( Fig. 41-2 ).
2.

A hand drill is then used, aligned with the downslope of the contralateral lamina, to drill through the cortical window into the contralateral lamina ( left ) to a depth of 30 mm ( Fig. 41-3 ).
3.

A ball-tip feeler is then used to palpate the hole to ensure that no cortical violation into the spinal canal has occurred ( Fig. 41-4 ).
4.

A 4.0 × 30 mm polyaxial screw (Mountaineer, DePuy, Raynham, Mass.) is then placed along the same trajectory ( Fig. 41-5 ).
5.

The small cortical window on the left is made again at the junction of the spinous process and lamina. However, the window is placed at the inferior portion of the lamina to prevent interference with the previously placed contralateral ( right ) translaminar screw ( Fig. 41-6 ).
6.

A hand drill is then used, aligned with the downslope of the contralateral lamina, to drill through the cortical window into the contralateral lamina ( right ) to a depth of 30 mm ( Fig. 41-7 ).
7.

A ball-tip feeler is then used to palpate the hole to ensure that no cortical violation into the spinal canal has occurred ( Fig. 41-8 ).
8.

A 4.0 × 30 mm polyaxial screw (Mountaineer, DePuy, Raynham, Mass.) is then placed along the same trajectory ( Fig. 41-9 ).