GENERAL CONSIDERATIONS

• Indications:
  • Sleep apnea secondary to micrognathia
  • Pierre Robin Sequence airway compromise
    • Compared to other surgical options MDO addresses the underlying issue of micrognathia.
    • When compared to tracheostomy for Pierre Robin Sequence, MDO has fewer subsequent procedures, lower costs, decreased level of home care, decreased ED visits, and decreased hospitalization.

• Potential complications include: 
  • Facial nerve injury: 9% [3/32] (Tibesar 2010). Even total facial nerve injury is possible (Belcher 2020)
  • Inferior alveolar nerve injury: Animal studies suggest distraction rates are associated with inferior alveolar nerve degeneration (Zhao 2018). Generally, rates should not exceed 1mm/day.
  • Tooth bud injury: Tooth agenesis is also frequently seen in Robin sequence making missing teeth difficult to relate causallity
  • Malocclusion (Cascone 2015), Open bite 28% [9/32] (Tibesar 2010)
  • Growth disturbance of the mandible
  • Need for further distraction
  • Infection
  • Trismus
  • TMJ ankylosis/injury
  • Device failure
  • Poor cosmetic result/hypertrophic scaring
  • Opioid withdrawal
  • Relapse
  • Poor vector of distraction
  • Fusion error (premature consolidation/fibrous union)

ANATOMY

• Inferior alveolar nerve: sensory and motor branch of mandibular division of V3. It courses posterior to the lingual nerve, deep to lateral pterygoid muscle and lateral to pterygomandibular raphe. It passes between the sphenomandibular ligament and the ramus of the mandible to enter the mandibular foramen along with the inferior alveolar artery and vein, travelling through the inferior third of the mandible in the mandibular canal. The nerve to the mylohyoid passes off before entering the mandible. The incisive nerve supplies the canine and incisors. The mental nerve exits the mental foramen near the second mandibular pre-molar tooth.
• Mandibular/Inferior alveolar canal: Opens on the lingual aspect of the mandible at the mandibular foramen.
• Marginal mandibular branch of the facial nerve: The nerve course is variable, originating from the inferior portion of the pes anserinus in the plane between the platysma and superficial investing fascia of the neck.
  • Studies in adults show that >50% have multiple branches. Early studies show that distance from the mandible ranged from 0.6cm about the inferior border to 1.2cm below with 47% above the inferior border (Ziarah 1981). Similar numbers have been found in later studies, also showing the nerve can drop below the inferior border of the mandible from <5mm from the gonion to approximately 33mm anterior to the Gonion. (Yang 2016)
  • In pediatric patients, and neonates in particular, there is less robust cadaver data though smaller proportions suggest tighter margins for error.
  • The Hayes-Martin maneuver, often used in submandibular gland resection, involves ligation of the posterior facial vein over the inferior portion of the submandibular gland and superior reflection of the investing fascia below the mandible to preserve the marginal mandibular nerve without identification. The same principle is used in this procedure.
• Facial vessels: The facial artery branches off the external carotid artery. It passes deep to the posterior belly of the digastric and submandibular gland. It then courses over the posteroinferior border of the mandible. In young children this occasionally requires ligation for access to the mandible. The facial vein begins just lateral to the nose and crosses over the body of the mandible before passing posteriorly beneath the platysma and cervical fascia. It travels superficial to the submandibular gland and the posterior body of the digastric muscle. It often needs to be ligated to access the mandible.

PREOPERATIVE PREPARATION

• Craniofacial CT with 3D reconstruction
• Planning session with KLS Martin
  • Plan vector of distraction
  • Define the position and angulation of osteotomies
  • May provide an opportunity to determine the appropriate size of distractor to be use
    • Zurich Distractors
    • Micro-Zurich distractors
  • Evaluated for relevant anatomy and interferences
    • Inferior alveolar nerve
    • Developing tooth buds
  • Titanium cutting guides are designed with predictive holes for the final position of the distraction devices as well a planned osteotomies
• Stereolithographic mandibular model is created with the osteotomy and predictive holes indexed
• Unidirectional KLS Martin distractors do not have laterality and come in one configuration with 4 plates
• Multi-plane distractors are designed with laterality
• The top or bottom plates are removed to create a right and left device, this allows for the turning mechanism to be posteriorly oriented.
• The devices once cut for laterality are prebent to the mandibular model with predictive holes.
• Once complete the distractors and mandibular model are sent for sterilization and delivery to the case.
• KLS will provide a PDF file with the planning summary which should be on hand during the surgical case

SUPPLY CONSIDERATIONS

• Elite Fissure Burrs 1, 1.2, 1.6
• 14 F Red Rubber Catheter
• Guarded needle monopolar Cautery
• Kerwin bipolar
• Mandible fracture tray
• KLS Screwdriver
• Twist Drill Stop W/ Notch 1.1x50mm
• Vari-Stim III Nerve Locator
• 4-0 Monocryl RB-1
• 4-0 Vicryl TF
• 3-0 Silk
• Custom Mandible model, cutting guide and distraction plates

ANESTHESIA CONSIDERATIONS

• Either oral or nasotracheal intubation is appropriate, with the goal for the ETT to go over the forehead. In many cases nasotracheal intubation is favored to stabilize the ETT. It is important to keep an eye on tube manipulation and reducing head turning to decrease the risk of accidental extubation.
• We do not generally turn the table but need to ensure the tube does not kink and is well secured so that the head can be moved from side to side.
• Some individuals may require “airplaning” of the bed to allow for better visualization and access to the cervical incision
• Long acting paralytics should be avoided for nerve monitoring and may be avoided due to difficultly airway anatomy
• Perioperative antibiotics (usually Ancef) are indicated.

OPERATIVE TECHNIQUE

1. Patient preparation (see illustrations above)
   1. Plan bilateral neck incisions, usually a minimum of 1.5 cm inferior to the inferior border of the mandible. The incision length will need to be designed to allow access from the angle of the mandible to about the mental foramen depending on the age and of the age of the patient and size of the mandible.
   2. ~2 ml of 1:200000 epinephrine is injected at the planned incision sites bilaterally (no local anesthetic)
   3. The patient is then prepped and draped. Care is taken to place a Tegaderm over the nose and mouth, leaving the edges of the mouth visible bilaterally. It is also important that the lateral neck and space behind the ear is visible.
2. Approach
   1. Skin is incised with a 15 blade down to platysma.
   2. Platysma is divided with hemostat dissection
   3. Once through the platysma a nerve stimulator is used frequently throughout the remainder of the dissection.
   4. Hemostats and bipolar are used to come down through the investing fascia of the submandibular gland, taking care to not prematurely come superior in an effort to protect the marginal mandibular nerve.
   5. The dissection is then carried superior, elevating the superficial investing fascia until encountering the inferior border of the mandible.
   6. If the facial vein and artery are identified these are ligated with 3-0 silk ties or clips.
3. Mandible
   1. The pterygomasseteric sling is then incised with monopolar cautery to enter a subperiosteal plane.  Incision directly on the inferior border in the most avascular portion of the sling will help minimize bleeding.
   2. Subperiosteal dissection is then carried out to expose the mandible widely with a #9 periosteal elevator.  You will want to visualize the mandibular angle, ascending ramus posterior and superiorly and the mental foramen anteriorly.
   3. In neonates and infants it may be prudent to consider completing the soft tissue dissections bilaterally before initiating the bony osteotomies as bleeding will result from the bone cuts and strict hemostasis is difficult to achieve
   4. The KLS Martin cutting/plate guide is then secured with screws (Typically 1.5mm screws to secure the guide). Distractor plate screw holes are then drilled (1.2 mm drill for micro-Zurich/1.5 mm for the Zurich).
   5. The osteotomy is started with a reciprocating saw or a 1.0 mm bur with irrigation in a monocortical fashion. A bur or the reciprocating saw is then used to carefully extend the osteotomy on the lingual side of the mandible. The cutting guides is removed and the osteotomy is completed with a T-handle chisel.  The depth of the chisel should still only be through the outer cortex to avoid damaging the IAN or developing tooth buds.  A common area for residual bony union is the lingual plate of the mandible.
   6. Next the distractor can be placed or the contralateral osteotomy can be completed first based on surgeon preference. 
4. Plating
   1. The pre-bent distractor is then placed over the pre-drilled screw holes and secured according to preoperative plan with 5 and 7 mm screws of the appropriate diameter based on the type of distractor placed.
   2. Before placing the distractor the activating arm and swivel need to be attached.  A determination on the size of the arm is made by laying the distractor over the osteotomy with an arm in place.  Based on the desired location of the skin incision for posterior exit of the arm an appropriate size is selected.  The distraction arm should protrude from the skin, but the junction of the swivel and arm should remain well buried in the tissue. 
   3. A 15 blade is used to make a post auricular stab incision for placement of the activation arm. The already attached arm is then placed inside a red rubber catheter and pulled through this incision.
   4. The distractor is then activated to ensure complete osteotomy was performed and then reversed back to the starting position
   5. The reverse lock-out mechanism is then activated. The contralateral side is then completed. The reverse lock-out mechanism prevents the device from being reversed or turned in the wrong direction.  There are times when you may consider not locking the device to allow for reversal of the distraction in the later portion of activation to correct asymmetries though this is not common.  Asymmetric turns can also be considered in this scenario.
5. Closing
   1. After copious irrigation 4-0 vicryl is used to reapproximate periosteum and pterygomasseteric sling, then the investing fascia platysmal and subcutaneous layer.
   2. A subcuticular continuous 4-0 monocryl suture is placed to close the skin along with a final layer of Dermabond.

POSTOPERATIVE CARE

• Distraction is generally initiated POD1 for infants and neonates. Older children and adolescents may warrant a 3-5 day latency phase
• There are a variety of distractors but for our most commonly used [KLS Zurich Micro Mid Driven with Ratchet 15mm 36H] one turn is equal to 0.6mm. BID turns result in 1.2mm/day for a goal of 12-15 mm of distraction (~10-12 days) depending on the patient.
• Bacitracin to pin distractor sites
• Unasyn while inpatient and the Augmentin until 24h after distractor arm removal
• Pain medication is not generally required for pin turns unless there is obvious discomfort
• When performed for PRS in neonates the patient returns to the ICU intubated. Extubation can often occur on POD 5-7 when agreed upon by ICU, Otolaryngology and Oral Surgery teams. This is before distraction is complete. When the procedure is performed in older children, extubation can often occur much earlier, in some cases immediately post-operatively. These individuals may be able to leave the hospital if caregivers are comfortable continuing the distraction at home.
• Once distraction is complete the transcutaneous activation arm can be easily removed with a release mechanism allowing the puncture wound to close. This can be done in clinic without local anesthetic. Antibiotics should be continued for 24 hours after the activation arms have been removed.
• Timing of distractor removal is usually at a minimum 3x the activation phase, though commonly in our practice we will typically await 3-5 months before removal. Due to the ability to remove the transcutaneous activation arm after distraction is complete there is little consequence in leaving the devices in slightly longer in our opinion.
• Post-operative polysomnogram is necessary to evaluate improvement and assessing the possible need for future intervention
• Post-operative 3D CT scan can similarly assess post operative airway volume and identify deficiencies in distraction

SAMPLE OPERATIVE NOTE

The patient was brought to the Operating room where general anesthesia was induced and intubated with a 3-0 uncuffed oral endotracheal tube and this was secured by the ENT team following direct Laryngoscopy and Bronchoscopy procedures. The table was moved slightly away from anesthesia and the patient was properly padded relieving all pressure points. The patient was prepped and draped in the standard fashion for a bilateral submandibular approach. A tegaderm was used to cover the oral cavity and nose. A formal time-out was executed.  

The patient was marked for a submandibular approach bilaterally, taking care to stay a minimum of 1.5 cm inferior to the inferior border of the mandible to avoid the marginal mandibular branch of the facial nerve. 2 cc of 1:200,000 epinephrine was infiltrated into the proposed surgical sites. A standard submandibular approach was then performed on the right, incising thru skin, subcutaneous tissue, platysma, and the superficial layer of deep cervical fascia, taking care to avoid the marginal mandibular branch of the facial nerve. A nerve stimulator was used throughout the dissection. The facial vein and artery were identified and ligated with 3-0 silk ties. The pterygomasseteric sling was incised and the mandible was exposed in a subperiosteal plane from the condylar region to the anterior body. No bony remodeling was required per the stereolithic model surgery to accept the pre-bent KLS Martin Zurich distractor. The mandible was marked for an osteotomy as planned during model surgery, taking care to achieve a distraction vector as horizontal as possible to facilitate anterior mandibular distraction. An osteotomy was performed with a 701 burr under copious irrigation. The osteotomy was completed with a T-handle chisel, assuring complete separation of the proximal and distal segments. A tooth bud and follicle were noted within the osteotomy site, but were not further manipulated. The site was then packed with a moist pack. An identical procedure was then completed on the left.

Attention was directed to the left posterior mandibular osteotomy. Next, the pre-bent 15 mm Micro Zurich distractor was placed on the left and secured to the proximal and distal segments with a total of *** KLS Martin screws of 5 and 7 mm lengths. A retromandibular nick incision was then made to accept the activation arm, below the ear. Blunt dissection with a hemostat was used to access the remainder of the surgical field. The activation arm with universal joint extension was then placed through the stab incision with an attached red rubber catheter, which was removed after the arm was secured to the distractor. The distractor was activated to approximately 4 mm assuring no remnants of bony union, then deactivated back to bony contact to provide for appropriate latency. The distraction arm showed appropriate clearance and access.  The reverse lock-out mechanism was activated. 

Attention was directed to the right posterior mandibular osteotomy. Next, the pre-bent 15 mm Micro Zurich distractor was placed on the left and secured to the proximal and distal segments with a total of *** KLS Martin screws of 5 and 7 mm lengths. A retromandibular nick incision was then made to accept the activation arm, below the ear. Blunt dissection with a hemostat was used to access the remainder of the surgical field. The activation arm with universal joint extension was then placed through the stab incision with an attached red rubber catheter, which was removed after the arm was secured to the distractor. The distractor was activated to approximately 4 mm assuring no remnants of bony union, then deactivated back to bony contact to provide for appropriate latency. The distraction arm showed appropriate clearance and access. The reverse lock-out mechanism was activated. 

The surgical sites were then copiously irrigated with normal saline and closed in layers with 4-0 Vicryl in continuous and interrupted fashion for the fascial and muscular/subcutaneous layers. A subcuticular closure was completed with 4-0 monocryl in continuous fashion. Dermabond was then applied over the incision line. The retromandibular distractor stab incisions and distractor arms were covered with bacitracin.

Sponge and needle counts were correct x 2. Care of the patient was turned over to the Anesthesia team and the patient was transported to the NICU in stable condition.

REFERENCES

Belcher RH, Phillips JD. Total facial nerve injury during mandibular distraction osteogenesis. Int J Pediatr Otorhinolaryngol. 2020 Sep;136:110182. doi: 10.1016/j.ijporl.2020.110182. Epub 2020 Jun 13. PMID: 32563840.

Cascone P, Basile E, Saccucci M, Di Carlo G, Angeletti D, Ramieri V, Polimeni A. Fast and early mandibular osteodistraction: the long-term follow-up of mandibular distraction osteogenesis on teeth position. J. Craniofac. Surg., 26 (8) (2015 Nov), pp. 2325-2328

Master DL, Hanson PR, Gosain AK. Complications of mandibular distraction osteogenesis. J Craniofac Surg. 2010 Sep;21(5):1565-70. doi: 10.1097/SCS.0b013e3181ecc6e5. PMID: 20856049.

Paes EC, Bittermann GK, Bittermann D, Muradin MM, van Hogezand R, Etty E, Mink van der Molen AB, Kon M, Breugem CC. Long-Term Results of Mandibular Distraction Osteogenesis with a Resorbable Device in Infants with Robin Sequence: Effects on Developing Molars and Mandibular Growth. Plast Reconstr Surg. 2016 Feb;137(2):375e-385e. doi: 10.1097/01.prs.0000475769.06773.86. PMID: 26818328.

Scott AR, Tibesar RJ, Lander TA, Sampson DE, Sidman JD. Mandibular Distraction Osteogenesis in Infants Younger Than 3 Months. Arch Facial Plast Surg. 2011;13(3):173–179. doi:10.1001/archfacial.2010.114

Tibesar RJ, Scott AR, McNamara C, Sampson D, Lander TA, Sidman JD. Distraction osteogenesis of the mandible for airway obstruction in children: long-term results. Otolaryngol Head Neck Surg. 2010 Jul;143(1):90-6. doi: 10.1016/j.otohns.2010.02.018. Epub 2010 May 21. PMID: 20620625.

Yang HM, Kim HJ, Park HW, Sohn HJ, Ok HT, Moon JH, Woo SH. Revisiting the Topographic Anatomy of the Marginal Mandibular Branch of Facial Nerve Relating to the Surgical Approach. Aesthet Surg J. 2016 Oct;36(9):977-82. doi: 10.1093/asj/sjw045. Epub 2016 Mar 29. PMID: 27025245.

Ziarah HA, Atkinson ME. The surgical anatomy of the mandibular distribution of the facial nerve. Br J Oral Surg. 1981 Sep;19(3):159-70. doi: 10.1016/0007-117x(81)90001-9. PMID: 6945120.

Zhao YH, Zhang SJ, Yang ZH, Liu XC, Lei DL, Li J, Wang L. Relationship of distraction rate with inferior alveolar nerve degeneration-regeneration shift. Neural Regen Res. 2018 Feb;13(2):360-365. doi: 10.4103/1673-5374.226426. PMID: 29557389; PMCID: PMC5879911.