A wider dissection will typically be performed for primary tumors compared to a trauma case.
3. Instrumentation for occipitocervical fixation
There are several plate systems available for the occiput. Their application is based on the same principles, and to illustrate these concepts, we will show the use of a plate placed in the midline, which allows for modularity and rotation when connecting to the rods.
Independently of the plate system used, its placement should be close to but still caudal to the external occipital protuberance (EOP).
Placement of the plate at the EOP will increase the risk of skin erosion.
A too-caudal position may compromise the foramen magnum.
The thickest part of the cranium is the dense ridge which runs vertically in line with the internal occipital crest.
The thickness of this crest is 11.5–15 mm in males and 10–12 mm in females, and it provides the best bone stock for screw purchase.
As you move laterally, this crest becomes thinner, and around 7–8 mm laterally to the midline, the bone thins out to a thickness of only 5–6 mm.
Another landmark with thicker bone is the superior nuchal line which runs horizontally.
Use templates centered in the midline on the posterior aspect of the occiput to determine the optimal size and shape of the plate.
Once the optimal plate is chosen, mark the location of the central cranial screw entry point with the plate in place.
Set the drill guide to 8 mm (female) or 10 mm (male) and drill the central cranial screw hole.
Probe the screw hole to verify that the anterior cortex is still intact.
If intact, continue drilling in 2 mm increments until the anterior cortex is penetrated.
Insert a screw of appropriate length through the plate into the predrilled hole.
After insertion of the first screw, there is enough flexibility in the system to allow for adjustments. Ensure the plate is flush with the skull and that it is level.
Insert the remaining screws in the order 2–5, using the same drill technique as for the first screw, ensuring bicortical purchase.
However, take care during drilling of the lateral holes (2 and 3) as the bone will be thinner than in the midline (4 and 5).
Cervical screw fixation
The C1 level is rarely included in the instrumentation for C1 and C2 tumors.
However, an uncompromised lateral mass may be instrumented upon the surgeon's preference.
Remove the posterior arch of C1 according to the preoperative plan.
Dissection should progress from normal to abnormal tissues to protect normal neurological elements and facilitate dissection.
The C2 nerve root should be decompressed as well to avoid occipital neuralgia.
Dissection of the tumor should progress from normal to abnormal tissues to protect normal neurological elements and facilitate dissection.
Use reverse-angle curettes and pituitary rongeurs to debulk the tumor.
Spinal cord mobilization should be minimized to reduce the risk of neurological injury.
Be aware of anatomical variation of the vertebral artery. Avoid injuries based on preoperative planning.
The goal is to achieve gross total resection.
Intraoperative navigation can be used as an adjunct to maximize resection accuracy.
Once the tumor is entirely resected, the goal of the surgery is met.
Decorticate the lamina, facets, and posterior aspects of the skull.
When using laminar screw fixation at C2, care must be taken not to decorticate deeply, as this might compromise screw fixation.
Alignment in the occipital cervical region
Align the head to allow for a horizontal gaze once the fusion is complete. Bend the rod accordingly.
Use the preoperative X-ray as a guide to properly align the occipitocervical junction during fusion.
Insert both rods when correct alignment is verified.
Place bone grafting material against the decorticated elements of the spine.
6. Intraoperative imaging
Before wound closure, intraoperative imaging is performed to check the adequacy of reduction, position, and length of screws, and the overall coronal and sagittal spinal alignment.
Note that in this case, the C2 vertebra was not instrumentable on the tumor side. The construct was extended lower than usual (C5) to account for this and the poor bone quality of this patient.
Lateral view of the above case
7. Posterior closure
Perform a multilayer closure as described in the approach.
For patients undergoing tumor surgery and/or with a history of radiation:
Plastic surgery should perform soft-tissue reconstruction to decrease the risk of wound complications
Intrawound vancomycin can be applied to decrease the risk of postoperative wound complications
Patients are made to sit up in bed on the first day after surgery. Bracing is optional but preferably omitted for patient comfort. 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.
Throughout the hospital stay, adequate caloric intake of a high-quality diet should be monitored.
Patients are generally followed with periodical x-rays at 6 weeks, 3 months, 6 months, and 1 year to monitor for hardware failure and with an MRI every 6 months for tumor surveillance.
Some primary benign tumors of the spine can recur years after surgery, and long-term tumor surveillance is important.