1 Preliminary remarks top
Anterior fixation is a useful technique to achieve sufficient decompression and interbody fusion. It is the superior technique for restoring cervical lordosis.
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.
Pitfall: As the surgeon is placed lateral to the midline of the patient, the true midline may be difficult to recognize and there is a tendency to direct the decompression to the contralateral side as shown in the illustration. This may lead to an incomplete decompression.
To prevent this, verification of anatomical landmarks using intraoperative imaging may be useful.
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.
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.
The procedure should be performed with adequate light and magnification; either loupes or a microscope.
2 Reduction top
Closed reduction is performed under image intensifier prior to skin incision. Extension or flexion is applied depending on the position of the fragments. This is followed by compression. Reduction should not include traction maneuvers.
3 Discectomy topenlarge
Prior to performing the discectomy, the level is confirmed with intraoperative fluoroscopy.
The following landmarks are identified:
- 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.
A small (nr 15) blade is used to open the annulus from uncinate to uncinate as close as possible to the endplates.
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.
The discectomy continues using a Pituitary rongeur forceps to remove the anulus and small curettes to scrape the endplates.
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. However, it is difficult to place distractors in the C2-C3 level.
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.
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.
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 Fusion topenlarge
Tricortical graft is harvested from the iliac crest and inserted in to the empty disk space. Great care must be taken to trim the graft so that it shares axial load with the plate. Alternatively, a cage filled with either bone graft or bone substitutes can be used.
Care should be taken not to over distract the segment with the implant as this may compromise the postoperative stability.
When choosing the plate length, care must be taken to prevent it from damaging the mobile disks below. The necessary plate length (blue) is confirmed under image intensifier.
Ideally the plate would extend as little as possible above and below the endplates of the injured level.
The plate is bent to accommodate the patient's 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.
Malrotation of the plate is commonly seen on the AP view and can be adjusted by temporarily removing one pin while adjusting the rotation.
Based on a preoperative measurement of vertebral body depth, screw holes are prepared with the appropriate depth. This is performed under lateral fluoroscopic guidance.
Screws are then inserted but not fully tightened until all screws have been applied.
Final hardware positioning is verified in lateral and AP view.