Paul Licina and Geoffrey N. Askin

Description

This extension osteotomy is performed posteriorly at the cervicothoracic junction to correct cervical kyphosis. Although originally described as being performed under local anesthesia with the patient in the seated position, the preferred technique entails general anesthesia, prone positioning, and spinal cord monitoring.

Expectations

The procedure should improve sagittal balance and restore forward gaze.

Indications

Severe cervical kyphosis associated with the following:

• Sagittal imbalance
  
• Loss of forward gaze
  
• Difficulty eating (jaw opening and swallowing)

Kyphosis severe enough to require corrective osteotomy is usually associated with ankylosing spondylitis or rheumatoid arthritis. Less commonly, kyphosis can result from trauma or cervical laminectomy.

Contraindications

Severe kyphosis localized to the thoracic spine may be more effectively corrected with thoracic osteotomies. Severe osteoporosis is a relative contraindication.

Special Considerations

Level of Osteotomy

The accepted osteotomy level is at C7-T1. This level is sufficiently cephalad for correction of the cervical deformity, while being sufficiently caudad to avoid the vertebral artery in the foramen transversarium. It is also at a level of the spinal canal that is relatively wide.

Positioning and Anesthesia

Head Control

It is best to use a halo ring attached to the bed. It facilitates precise and secure positioning as well as subsequent head manipulation.

Torso Support

A four-poster frame is usually employed. It may need to be elevated off the bed to accommodate the cervicothoracic kyphosis, and it allows the head to be attached to the bed via the halo ring.

Visualization

The required degree of correction is difficult to estimate. The use of transparent plastic drapes allows the surgeon to see the relative position of the head and torso to facilitate visual confirmation of adequate reduction.

Intubation

The flexed position and stiffness of the neck usually poses intubation problems. Preoperative anesthesia assessment includes reviewing lung and cardiac function, and developing an intubation plan. An awake intubation is usually undertaken, using a nasotracheal tube or fiberoptic laryngoscope.

Neurologic Assessment

Spinal cord injury during reduction of the osteotomy, and even during positioning, is a significant risk. For this reason, spinal cord monitoring, ideally both motor and somatosensory, is required.

Tips, Pearls, and Lessons Learned

Preoperative Planning

The following needs to be obtained:

A useful way to gauge the degree of correction required on the lateral x-ray is to trace the spine on tracing paper, cut the paper at the osteotomy level, and then rotate the pieces until sagittal balance has been achieved. The angle between the cut edges then gives the required osteotomy angle (Webb technique).

It may also be helpful to obtain a biomodel (a custom polymer model of the spine based on the CT scan data). The osteotomy and fixation can be planned preoperatively, and the model can be sterilized and used intraoperatively to facilitate three-dimensional visualization.

Control of Osteotomy Reduction

Correction of the osteotomy is often rapid, and precise control may not be possible. Resultant translation can cause spinal cord injury. A way of minimizing this risk is to use a modular cervicothoracic fixation system with cervical lateral mass and thoracic pedicle clamps that allow the rod to slide through them. Once the osteotomy is completed, a temporary malleable rod (a useful trick is to use an intubation stylette) is inserted and the cervical clamp screws are tightened to secure the rod cephalad to the osteotomy. As the osteotomy is corrected, traction is applied to the caudad end of the rod, allowing it to bend and slide through the thoracic clamps in a controlled fashion, thereby minimizing the risk of translation (Mehdian technique).

Key Procedural Steps

Preparation

The patient is intubated, positioned, and monitored as described above. A long midline approach is made, exposing C3 to T4. Imaging is used to confirm the level.

Instrumentation