Craniocervical Instrumentation Techniques

Craniocervical fixation is used for the treatment of instability owing to several pathological conditions. Initial operative techniques to stabilize the craniocervical junction involved onlay fusion. Onlay fusion is effective but requires prolonged immobilization in a halo vest. The addition of instrumentation provides immediate stability and may allow patients to forgo the use of a halo vest while achieving higher fusion rates. Initially a rod was bent and secured to the craniocervical area using sublaminar wires ( ▶ Fig. 8.1).

Fig. 8.1 Ohio Medical Instruments (Schaerer Mayfield USA, Cincinnati, Ohio) loop secured using sublaminar wires for craniocervical fixation.

Technical difficulties associated with passing sublaminar wires and suboccipital wires and biomechanical shortcomings of shorter segment constructs led to the development of plate and screw–based constructs for occipitocervical fusions. The plate and screw constructs are significantly more rigid than previous sublaminar wire constructs. Grob et al reported the use of plates and either transarticular screws or subaxial lateral mass screws in craniocervical fusions with excellent results.

8.2 Patient Selection

A wide variety of pathologies affect the craniocervical junction including congenital abnormalities: trauma, tumors, and degenerative conditions such as rheumatoid arthritis ( ▶ see text box; ▶ Fig. 8.2). Diseases causing instability at the craniocervical junction result in pain, myelopathy, and progressive disability. Craniocervical instrumentation results in a significant functional motion loss; therefore, all surgical options are considered before selecting patients for craniocervical instrumentation. Up to 56 degrees of cervical rotation occur at C1–2, and 8 degrees of rotation occur at C0–1. The craniocervical area is also responsible for most cervical sagittal plane rotation (flexion and extension).

When possible, instrumentation is limited to C1–2, excluding the occiput, to preserve cervical flexion and rotation. The development of a lateral mass screw placement technique has limited the indications for craniocervical instrumentation. Craniocervical instrumentation is required when instability involves the C1–0 segment and when C1–2 instrumentation is not feasible. Craniocervical fixation may also be required to salvage a C1–2 pseudarthrosis or following resection of the odontoid.

Pathology

Disease

Basilar invagination

Rheumatoid arthritis

Squamous cell carcinoma

Multiple myeloma

Ossification of the posterior longitudinal ligament

Down syndrome

Ossification of the posterior longitudinal ligament

Fig. 8.2 Sagittal T1-weighted magnetic resonance imaging shows an os odontoideum with anterior spinal cord compression.

8.3 Preoperative Preparation

Fusion should be kept as short as possible but include all pathological segments. If there is additional subaxial instability, fusion might have to be extended to include the lower cervical spine. If stabilization of the lower cervical spine is indicated in cases of severe osteoporosis and rheumatoid arthritis, especially with kyphotic deformity, it might be advisable to include the cervicothoracic junction and extend the fusion to the upper thoracic spine.

Imaging studies including flexion and extension plain films are important to assess the patient’s overall sagittal alignment. Preoperative cervical traction is appropriate for patients with cervical deformity.

8.4 Operative Procedure

8.4.1 Positioning

The patient is placed in the prone position. In an unstable spine, the cervical alignment is checked using fluoroscopy or plain radiographs after positioning the patient; if necessary, closed reduction is performed. A neutral craniocervical position is essential. Proper alignment allows the patient to look comfortably straight ahead after surgery. Excessive craniocervical flexion positioning and fusion can result in postoperative difficulty with swallowing and with maintaining a forward gaze.

Neurologic status may be monitored using electrophysiological monitoring, including somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs). Any changes in SEP or MEP monitoring after positioning may indicate the need to reposition.

8.4.2 Approach

A posterior midline incision is performed. The occiput, the posterior ring of the atlas, the posterior elements of C2, spinous processes, vertebral arches, and lateral masses of those lower cervical spine vertebrae to be included in the fusion are exposed subperiosteally. Careful attention is used to avoid injury to the vertebral arteries laterally near the arch of C1. The large venous plexus around the vertebral artery at the craniocervical junction is also a possible source of heavy bleeding. Meticulous dissection will reduce blood loss. Exposure of the occiput is up to the inion. Lateral exposure on the occiput is usually 4 cm. The lateral masses of the subaxial spine are well exposed for placement of lateral mass screws. Decompression of the spinal canal is performed if necessary. Bone graft from the posterior iliac crest is harvested separately.

8.4.3 Instrumentation

Several instrumentation systems exist for craniocervical fixation. The systems either involve a midline occipital plate, a Y-shaped plate, or a rod connected to a plate ( ▶ Fig. 8.3). The occipital bone in the midline is significantly thicker than the occipital bone laterally. The cortex lateral to the midline is less than 5 mm thick. The thicker central bone allows for superior screw purchase and a smaller risk of perforating the dura with drilling. Dural lacerations are not uncommon and usually are sufficiently sealed by placing a screw.

Fig. 8.3 Sawbone model with a craniocervical fixation system (Stryker Corporation, Kalamazoo, Michigan). The lateral plates are angled so that the screws are placed in the midline keel.

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