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Pipsa Ylanko, AOSpine Global Education Manager

Executive Editor: Luiz Vialle

Authors: Carlo Bellabarba, Marcelo Gruenberg, Cumhur Oner

Subaxial cervical trauma - A2 Anterior plating

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Glossary

1 Preliminary remarks top

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Anterior fixation is a useful technique for anterior decompression and reconstruction of the anterior column.

Direct decompression from disk or bone material can be performed directly without mobilization of the neurological structures.

Visualization of the dura allows direct confirmation of complete decompression.

Nerve roots are better identified from a posterior approach, but experienced surgeons can also perform an anterior foraminotomy.


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Preoperative evaluation of potential anatomic variations in the course of the vertebral artery is mandatory. Unidentified anatomical variations may increase the risk of compromising the artery during decompression.

2 Indications for anterior decompression top

Indications for anterior decompression

Indications for decompression during anterior reconstruction includes:

  • The presence of a traumatic disc herniation causing neurologic injury (discectomy alone)
  • The need to remove a portion or entire vertebral body followed by reconstruction for stability, or for relief of symptomatic neural compression
  • Kyphotic angulation with ventral compression.

Corpectomy is performed when the anterior column is severely compromised and/or to remove bone material from the spinal canal. In this procedure diskectomies above and below the fractured vertebra are performed first, allowing visualization of the upper and lower limits of the spinal canal.


Visualization

The procedure should be performed with adequate light and magnification; either loupes or a microscope.

3 Discectomy technique top

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Prior to performing the discectomy, the level is confirmed with intraoperative fluoroscopy.

The following landmarks are identified:

  • Midline
  • Unciform process

The midline will dictate the AP orientation of the discectomy.

The unciform processes dictate the lateral borders of the discectomy, establishing the safe area from the artery. This will leave a 3mm safe zone to the normal anatomy of the vertebral artery.


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A small (nr 15) blade is used to open the annulus from uncinate to uncinate as close as possible to the endplates.

Pearls

To help stop a slipping blade, a Frasier tip suction is held in place in the direction the blade is cutting.

To prevent accidental durotomy and spinal cord transection, the annulotomy should not go deeper than 11 mm. The sharp edge of the nr 15 blade is 11 mm and can be used as a depth gauge.


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The discectomy continues using a Pituitary rongeur forceps to remove the anulus and small curettes to scrape the endplates.


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The use of a distractor or an intervertebral distractor will facilitate the removal of the posterior half of the disk and visualize the posterior longitudinal ligament.

The normal height of the area should be reconstructed. However, care should be taken not to over distract.

A complete discectomy will allow good visualization of the spinal canal and enhance fusion.


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Meticulously remove all cartilage from the endplates. Pieces of cartilage may inhibit fusion if present either on the endplates or in the bony material used for the fusion.


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A small probe is used to ensure that no fragments are left in the area behind the vertebra which is not directly visualized, or in the foramen.

Magnification and correct illumination is essential to make the final decompression.

4 Full corpectomy technique top

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Corpectomy technique

Prior to performing a full corpectomy, both the superior and inferior discs are removed to define the safe depth of bone resection.

Segmental vessels are identified and ligated in the mid vertebral body, away from the natural foramen. These vessels may already be disrupted due to the trauma.


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Laterally the corpectomy is limited by the medial boarder of the unciform process.

The unciform processes dictate the lateral borders of the corpectomy, establishing the safe area from the artery. This will leave a 3mm safe zone to the normal anatomy of the vertebral artery.


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At this point, the fractured portion of the vertebral body (but not the posterior third) is removed using a combination of Leksell rongeurs and osteotomes.

If a cage is used for the reconstruction, an instrument producing larger fragments of bone is preferred as it facilitates filling of the cage.


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A burr is used to remove the posterior portion of the vertebral body as the spinal canal is approached.


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The spinal canal is decompressed by the resection of the posterior wall of the vertebral body.

The posterior cortex should be thinned with the burr to an eggshell. Retropulsed bone fragments can be removed with curettes and thin footplate Kerrison punches.

This is optimally done with a high speed burr and curettes under loupe or microscopic magnification.


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Pearl: protection of the dura

Care should be taken to protect the dura. Epidural venous bleeding can be troublesome at times, so meticulous hemostasis with bipolar cautery, cottonoid patties, and hemostatic adjuncts can be helpful.

5 Reduction top

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In A type fractures, spine alignment will be nearly completely restored by the distraction performed during corpectomy.

The normal height of the area should be reconstructed. However, care should be taken not to over distract.


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The over distracted hole will be filled with a larger cage or bone graft and stabilized with a plate. But, over-distracted facet joints will make this construct unstable leading to implant failure and eventually pseudo arthrosis.

If this is situation is recognized in the postoperative X-ray, this would be a clear indication for additional  posterior fixation (360° procedure)

6 Fusion after full corpectomy top

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The following two options are available for reconstruction after corpectomy:

  • Tricortical graft and plate
  • Mesh cage and plate

Care should be taken not to over distract the segment as this may compromise the postoperative stability.


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Reconstruction using tricortical graft and plate

Tricortical graft is harvested from the iliac crest and inserted in to the defect. Great care must be taken to trim the graft so that it shares axial load with the plate.

Allograft may also be used.

After insertion of the graft, the Caspar pins are removed.


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When choosing the plate length, care must be taken not to prevent it from damaging the mobile disks above and below.


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The plate is finally bent to accommodate the patient's lordosis and fixed with two screws in each vertebra.


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Reconstruction using Mesh cage and plate

The corpectomy defect is measured using caliper.


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A mesh cage of the largest possible diameter is cut to a corresponding length.


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The cage filled with tightly packed bone obtained from the corpectomy.


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End plate rings should be added in patients with osteoporosis. They are optional in patients with normal bone. These often have variable angulation and can be used to accommodate non parallel endplates.


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The cage is inserted and tapped into its final position under lateral fluoroscopic monitoring.

The Caspar pins are removed.


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When choosing the plate length, care must be taken to prevent it from damaging the mobile disks above and below.

Note: Dynamic plates should be avoided in trauma as their principles often conflict with the goals of stabilization in the unstable spine.

Variable angle plates with locking screws are also an option if thought to be necessary.


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Ideally the plate would extend as little as possible above and below the endplates of the injured level.


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The plate is bent to accommodate the patients lordosis and fixed in place with two temporary pins placed in holes diagonal to each other.

The appropriate positioning of the plate is verified in AP and lateral views.


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Malrotation of the plate is commonly seen on the AP view and can be adjusted by temporarily removing one pin while adjusting the rotation.


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Based on a preoperative measurement of vertebral body depth, screw holes are prepared with the appropriate depth. This is performed under lateral fluoroscopic guidance. of appropriate length selected and


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Screws are then applied but not fully tightened until all screws have been inserted.


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Final hardware positioning is verified in lateral and AP view.