Posterior vault expansion by distraction osteogenesis

Posterior cranial vault distraction is being increasingly used for the treatment of Syndromic synostosis. Many patients have turribrachycephaly, and expansion of the posterior vault allows for more complete total vault reshaping. Conventional reshaping in these patients is often associated with a high degree of relapse. Distraction gives one the ability to not only expand posteriorly to a greater degree, but as the brain is expanded as well, there may be less relapse. Many people consider it to be the procedure of choice in the management of the syndromic patient.

Although no specific distraction devices for posterior cranial vault distraction are commercially available at the time of writing, mandibular devices utilizing 1.3 to 2.0 mm with a 25 to 40 mm barrel length can be used.

With the patient in a prone position with the head resting on a horseshoe head rest, exposure of the posterior half of the skull is made via a coronal incision.

After exposure of the posterior cranial vault, a craniotomy of the occiput and the parietal regions is outlined.

Burr holes are placed by the neurosurgeon along the planned osteotomy lines and an epidural dissection between these points is made.

The osteotomies are then completed using a craniotome.

Note: The bone flap is not removed during this procedure. Leaving the dura attached to the endocranial surface of the bone flap maintains the vascular supply to the segment, and allows the brain to be expanded concurrently.

"Barrel-stave" osteotomies with outfracture are performed in the inferior occipital segment to avoid any step-off between the distracted segment and the cranial base. The newly positioned barrel-staves may be left to float or are stabilized with a long resorbable plate.

In case a posteroinferior trajectory is chosen, an osseous wedge is removed from the junction of the craniotomy segment and the posterior vault to ensure unhindered travel of the distracted piece.

Two distractors, one on each side, are adapted to the underlying bone and placed in a parasaggital colinear position, oriented with a trajectory either directly posteriorly or posterior inferior. As it is a single vector device one must be certain that the position fits the vector chosen. The distractor is then attached with at least five 4 mm titanium screws per footplate.

The distractor is activated to ensure proper function and free travel of the bone flap. The distractors are then returned to neutral position.

This 3D-CT scan shows the distractor in place.

The activation arm of the distractor is brought out through a stab incision either in the posterior surface of the scalp or the anterior scalp flap.

After a latency period of 3-5 days, distraction commences at the rate of approximately 1 mm/day. It is common practice to instruct a relative of the patient how to perform the distraction. Periodic (usually weekly) review in the office is carried out until the desired position is reached (15-30 mm).

Following the completion of distraction, the device is left in place for 2-3 months to allow for consolidation of the regenerate bone and is then removed.

Most surgeons favors placement of a bulb suction drain under the scalp for 3-5 days. Resorbable skin sutures are often used.

A circumferential head dressing is utilized for 48 hours. The neurosurgeon may request placement of a lumbar drain if significant dural tears have occurred during surgery. Patients should spend at least 1-2 days in an intensive care unit for neurological monitoring.

Keeping the patient’s head in an upright position postoperatively may significantly improve periorbital edema and pain. Some surgeons use injectable corticosteroids during surgery to reduce periorbital swelling.

To prevent orbital emphysema, nose-blowing should be avoided for at least 10 days.

The following perioperative medications are controversial. There is little evidence to make strong recommendations for postoperative care.

• Avoidance of aspirin or nonsteroidal antiinflammatory drugs (NSAIDs) for 7 days.
• Analgesia as necessary.
• Antibiotics (many surgeons use perioperative antibiotics. There is no clear advantage of any one antibiotic, and the recommended duration of treatment is debatable.).
• Nasal decongestant may be helpful for symptomatic improvement in some patients.
• Steroids may help with postoperative edema. Some surgeons have noted increased complications with perioperative steroids.
• Ophthalmic ointment should follow local and approved hospital protocol. This is not generally required in case of periorbital edema. Some surgeons prefer it. Some ointments have been found to cause significant conjunctival irritation.
• Regular perioral and oral wound care has to include disinfectant mouth rinse, lip care if intraoral incision has been used.

Postoperative examination by an ophthalmologist may be requested, although sever periorbital edema may prevent useful assessment. The following signs and symptoms are usually evaluated:

• Vision
• Extraocular motion
• Diplopia
• Globe position
• Lid position

Postoperative imaging has to be performed within the first days after surgery to verify accuracy of surgery. 3-D imaging (CT, cone beam) is recommended.

Remove sutures from skin after approximately 7-10 days if nonresorbable sutures have been used.
Apply ice packs for the first 12 postoperative hours as able although infants and young children do not tolerate this well (may be effective in a short term to minimize edema).
Avoid sun exposure and tanning to skin incisions for several months.

Soft diet can be taken as tolerated until there has been adequate healing of any maxillary vestibular incision. In children and infants age appropriate diets are then prescribed.
Patients in MMF will remain on a liquid diet until such time the MMF is released.

Clinical follow-up depends on the complexity of the surgery, and whether the patient has any postoperative problems. Most patients are discharged at postoperative day 3-5 and seen again in 2-3 weeks.

• In patients undergoing monoblock or Le Fort III distraction, distraction typically begins at day five at 1 mm/day and is assessed weekly with plane radiographs and clinical examination until the desired position is reached. After advancement a period of consolidation of 1-3 months is recommended before the retractors are removed.
• In patients undergoing conventional advancement with intermaxillary fixation, MMF is kept in place for 4-6 weeks. Routine oral hygiene is prescribed. Patients with arch bars and/or intraoral incisions and/or wounds must be instructed in appropriate oral hygiene procedures. The presence of the arch bars or elastics makes this a more difficult procedure. A soft toothbrush (dipped in warm water to make it softer) should be used to clean the surfaces of the teeth and arch bars. Elastics are removed for oral hygiene procedures. Chlorhexidine oral rinses should be prescribed and used at least 3 times a day to help sanitize the mouth.
  For larger debris, a 1:1 mixture of hydrogen peroxide/chlorhexidine can be used. The bubbling action of the hydrogen peroxide helps remove debris. A Waterpik® is a very useful tool to help remove debris from the wires. If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions as this may lead to wound dehiscence.

The patient needs to be examined and reassessed regularly and often. Additionally, ophthalmological, ENT, and neurological/neurosurgical examination may be necessary. If any clinical signs for meningitis or mental disturbances develop, professional help has to be sought. Due to the young age of many patients, routing CT-scans are performed only if clinically indicated to avoid excessive radiation exposure.