Interpositional nerve graft

The strategy for nerve identification depends on the site of the cut or laceration.

General considerations regarding nerve repair techniques can be found here.

Lacerations within the parotid gland are first explored in attempt to identify the cut distal and proximal ends.

The laceration may need to be extended.

If the proximal nerve cannot be identified after extension, two options can be considered in order to identify the main trunk of the facial nerve:

• A formal facelift or parotidectomy type of incision
• Extension of the laceration into a face lift or parotidectomy type incision

There are two common ways to identify the main trunk of the facial nerve:

• Identify the tragus of the ear. Dissect down the cartilage of the tragus to its inferior end called the “tragal pointer”. The nerve is found 1 cm inferior, anterior, and medial to the pointer.
• Identify the posterior belly of the digastric muscle. The nerve can be found immediately superior to the upper border of the muscle and at the same depth.

As a landmark for the facial nerve, the styloid process should be used with caution because it is situated immediately deep to the nerve.

A dissection is performed along the nerve through the parotid gland until the lacerated nerve branch is found.

Intraoperative direct nerve stimulation may be possible up to 7 days from time of injury.

If not successful, the distal nerves are identified as they exit the parotid.

The distal nerves are dissected in retrograde fashion (from distal to proximal) through the parotid gland until the lacerated branches are identified.

The main trunk of the facial nerve is identified through a limited facelift type of incision or parotidectomy (incorporating the laceration if possible).

There are two common ways to identify the main trunk of the facial nerve:

• Identify the tragus of the ear. Dissect down the cartilage of the tragus to its inferior end called the “tragal pointer”. The nerve is found 1 cm inferior, anterior, and medial to the pointer.
• Identify the posterior belly of the digastric muscle. The nerve can be found immediately superior to the upper border of the muscle and at the same depth.

As a landmark for the facial nerve, the styloid process should be used with caution because it is situated immediately deep to the nerve.

Once the main trunk is identified, dissect posteriorly until the lacerated nerve branch is found.

If greater exposure is required, a parotidectomy incision may be helpful.

If necessary, a formal drill out of the temporal bone can be performed to identify the mastoid segment of the facial nerve.

Both nerve ends are typically identified through the laceration, which can be extended if needed.

The facial nerve branches are identified as they exit the anterior extent of the parotid gland.

The branches are dissected from proximal to distal until the lacerated ends are identified.

Intraoperative direct nerve stimulation may be possible up to 7 days from time of injury but the nerve must be stimulated distal to the injury.

Several skin surface landmarks can be used to identify the various branches of the facial nerve:

• The temporal branch can be found by drawing a line 2 cm lateral to the lateral canthus, crossing over the zygomatic arch marks, to the incisura of the ear.
• The buccal branch can be found by drawing a line from mid philtrum to incisura. The nerve can be found where this line crosses the anterior parotid gland, often following the Stenson's duct anteriorly.
• The marginal mandibular branch is located at least 2 cm superior to the mandibular border and superficial to the facial artery and vein

The remaining branches vary in anatomic location and there are no consistent landmarks to aid in identification.

Note: it is not possible to directly graft into a muscle, it is always necessary to identify a distal nerve ending. In case no distal end is available, other static or dynamic options should be considered.

Sensory nerves are routinely used for grafting, as they cause less functional deficits. The most common sensory nerves used are the sural nerve and the great auricular nerve.

Other options are the medial or lateral antebrachial nerves.

The selected nerve is harvested.

The facial nerve is examined for viable fascicular bundles. This can be done:

• Clinically, including the use of operating microscope with high magnification
• Using frozen section

The grafting technique depends on the region where the nerve gap is identified:

• Distal branches
• Pes anserinus
• Main trunk
• Upper or lower divisions
• Skull base (intraosseous)

The proximal and distal ends are found and one cable graft is used with direct coaptation.

The gap is identified and multiple cable grafts are coapted to the proximal end. May consider using fibrin glue for coaptation.

Direct coaptation is used to coapt the graft to the distal branches.

Selective reinnervation could be considered to reduce the incidence of synkinesis postoperatively.

The gap is identified and multiple cable grafts can be used for a tension free repair.

May consider using fibrin glue for coaptation.

Selective reinnervation could be considered to reduce the incidence of synkinesis postoperatively.

Fascicular repair at this level may reduce the risk of synkinesis.

Grafting within the skull base is technically challenging. A temporal bone drill out is required and prognosis for recovery is often poor.

If the proximal end is not available, even after drill-out of the temporal bone, then consider a different motor nerve, such as cross face nerve graft, masseteric nerve (V-VII), or hypoglossal nerve (XII-VII).

Selective reinnervation may be considered to reduce the incidence of synkinesis postoperatively.

Static suspension may be used to augment reinnervation procedures, in order to improve facial symmetry at rest, especially during the period of facial nerve recovery.

Routine wound care is all that is necessary for the majority of the procedures.