Posterior C1-C2 fusion

C1 and C2 are anatomically unlike any other vertebrae in the spine. Their unique anatomy allows for 50% one's flexion-extension motion at the occipital C1 joint and 50% of one's rotational motion at the C1-C2 joint. Consequently, they are the most important vertebrae for cervical range of motion.

When treating fractures of these two vertebrae, every effort should be made to avoid arthrodesing these two joints. However, for dislocations, fusion would be the best option.

The goals of treatment are to stabilize the spine until the fractures have healed or to perform an arthrodesis in cases where stability cannot be achieved after healing is completed (such as with ligament ruptures).

If closed reduction and immobilization is not possible, one should consider open reduction and internal fixation followed by subsequent removal of instrumentation for cases that will become stable once the fractures have healed.

The vertebral artery trajectory must be fully evaluated prior to any surgery in this area.

This procedure is performed through a posterior approach with the patient placed in the prone position.

Reduction may be performed by gentle traction, especially in acute cases. If not achieved or in more delayed cases, surgical reduction is indicated.

This involves soft tissue release (ligaments, capsule and scar tissues fond in delayed presentation) followed by gentle manipulation.

The final reduction must be confirmed using a C-arm.

The oldest technique involved wires and structural autograft. This is rarely used and will not be described here.

Magerl first described the use of trans articular screws. This is a relatively simple and inexpensive way to fixate the C1-C2 joint. The disadvantage is that screw insertion requires fluoroscopy. Furthermore, the C2 pars must be large enough to accommodate a 3.5 mm diameter screw.

• Posterior trans articular screw insertion

Goel and subsequently Harms described the use of C1 lateral mass and separate C2 fixation techniques.

C1 can be fixed using either lateral mass screws that start just caudal to the posterior arch or that start on top of the posterior arch and then capture the lateral mass. The latter can only be used if the posterior arch is thick enough to allow for the screw.

• C1 lateral mass screw insertion

C2 can be fixed using either of the three techniques:

• C2 laminar screw insertion
• C2 pedicle screw insertion
• C2 pars screw insertion

Be aware that some posterior arches have a ponticulus posticus that appears to be a thick posterior arch, but in fact is a small bridge of bone that overlies the vertebral artery.

This X-ray shows the ponticulus posticus.

Since there are only two screws on each side there is no need for rod bending. A straight rod is placed and tightened. Keep the rods as short as possible.

If there is spreading of the ring of C1, or a laterally displaced intra articular fracture, one can use the C1 lateral mass screws to reduce the displacement. After placement of bilateral C1and C2 screws and rods, one can place a cross link and compress the rods together, thereby reducing the fracture.

An alternative in patients who have an anatomic reduction of the lateral mass fracture, but in whom C1 lateral mass fixation is not possible, one can instrument up to the skull but only fuse the C1-C2 joint. Once the fractures have healed, the instrumentation can be removed.

Cancellous allograft placed dorsally over the lamina does not work in the vast majority of cases and should be avoided. One can place cancellous allograft intra-articulary after decorticating.

To decorticate the joint, reflect the C2 nerve cranially.

Burr into the joint or use a curette to scrape the articular cartilage. Be aware that the vertebral artery can in some cases be just below the articular surface of C2. This can be verified by CT scan.

If an intra-articular fusion is not performed, one must use a structural cortical cancellous graft to bridge the C1 posterior arch to the C2 lamina. Auto iliac crest bone graft is the most reliable.

Fashion the bone graft as illustrated.

If a Goel/Harms technique has been used, place a wire under the left rod over the graft and under the right rod and cinch it in place to push the graft onto the decorticated C1 posterior arch and C2 lamina.

Add additional cancellous autograft strips to fill the voids between the lamina of C2 and the structural autograft.

The bone graft is identical as for the Goel/Harms technique, but the wiring technique differs. Since there are no rods, the graft is secured with wires. A loop of wire is passed under the arch of C1, and the two free ends are passed through this loop.

A second wire is passed through the spinous process of C2.

After decorticating the C1 posterior arch and the C2 lamina, the graft is placed and the two wires are twisted together over the graft.

Add additional cancellous autograft strips to fill the voids between the lamina of C2 and the structural autograft.

Patients are made to sit up in the bed on the evening following the operation.

A collar is commonly used following surgical stabilization to moderate patient activity.

The purpose of a collar is to prevent ranges of motion outside of limits deemed unfavorable for fracture healing. Collar is optional.

Patients with intact neurological status are made to stand and walk on the first day after surgery. Patients can be discharged when medically stable or sent to a rehabilitation center if further care is necessary. This depends on the comfort levels and presence of other associated injuries.

Patients are generally followed with periodical x-rays at 6 weeks, 3 months, 6 months, and 1 year.