Nerve Graft Techniques - Clinical Tree

Introduction

Neural injury, repair, and subsequent recovery are widely studied, since these topics relate to the entire human body. There are few other regions of the body where impaired nerve function can be more devastating than in the head and neck. Peripheral cranial nerves contribute to our most personal attributes, such as speech, facial expression, and the complex neural coordination of deglutition. The technical aspects of nerve repair have been refined; however, challenges persist in terms of the functional outcomes.

Any patient undergoing head and neck surgery faces risks to multiple cranial nerves. Often in our field, a nerve must be identified and dissected for preservation or resected as part of an oncologic procedure. Oncologic goals supersede the preservation of neural structures when there is curative intent; however, even when the nerve can be preserved, extensive dissection can cause functional issues that may not be entirely relieved.

The facial nerve (FN) is the most commonly reconstructed nerve in the head and neck. The FN is also the most studied in regard to outcomes. The loss of facial expression removes the visible thumbprint of our personalities in day-to-day interactions and can be devastating both emotionally and functionally. Unlike some of the other cranial nerves that are affected in oncologic surgery or even with the removal of benign tumors—such as cranial nerve VIII during acoustic neuroma surgery or the spinal accessory during radical neck procedures—a repair of the FN may be neither indicated nor performed.

Key Operative Learning Points

1.
Tension-free repair is imperative. Placing the nerve in a “lazy s” configuration within the wound is helpful to ensure that there is adequate laxity.
2.
Preoperative assessment of the patient’s smile on the normal side of the face should determine what facial motion and vector are needed to recreate a natural reanimation of the paralyzed side.
3.
Success in cross-FN grafting for smile reanimation relies on choosing the appropriate donor nerve that is associated only with movement of the oral commissure and upper lip, that is, the nerve that mimics the preoperative smile of the normal side.

Preoperative Period

History

Patient Selection

The severity and anatomic location of the injury are important predictors of how or when a repair should be performed.

The viability of the proximal nerve, distal nerve, and musculature and motor end plates are key variables in the algorithm of neural repair.
The time from injury to repair plays a key role in designing a reconstructive plan.
Immediate repair will typically yield the best outcome, as Wallerian degeneration is complete after 3 days, after which the distal nerve segments can no longer be stimulated.
The patient’s goals and wishes must be discussed prior to intervention. Patient expectations must be managed to prepare for incomplete recovery, which can occur even with the best of reconstructive efforts.

Past Medical History

History of diabetes mellitus and smoking may impair wound healing.
Medical comorbidities may limit the use of general anesthesia and therefore also the reconstructive options.
History of soft tissue loss in the face should be noted.
Negative margins or absence of recurrent tumor must be confirmed.

Past Surgical History

History of previous FN repairs
History of previous facial surgeries, including skin cancers
Surgery performed on potential donor sites

Physical Examination

Extent of facial paralysis throughout the regions of the face—that is, paresis versus paralysis, upper versus lower division, individual nerve branches
Presence of soft tissue loss
Evaluation of donor sites (neck, leg, groin)

Imaging

None necessary

Indications

Suspicion of injury to the FN with immediate loss of function
Mechanism of injury consistent with FN disruption
Resection of FN segment as part of en bloc cancer surgery
Iatrogenic injury during surgery involving the tissues surrounding the FN

Contraindications

Chronicity of facial paresis such that the motor end plates associated with the muscles of facial expression are no longer viable
Resection of distal FN branches and facial musculature
Comorbidities precluding general anesthesia
Unrealistic patient expectations as to level of recovery with nerve repair and grafting

Preoperative Preparation

Considerations for Type of Procedure to Be Chosen

All attempts should be made to do a primary neurorrhaphy when there has been traumatic or iatrogenic injury.
In the traumatic or oncologic setting, there may be loss of tissue so that the surgeon will be unable to perform a tension-free coaptation. In this situation the patient should be asked for consent to the use of appropriate donor sites for nerve graft harvest.
Donor nerves are selected based on the caliber, length, and branching pattern needed.
The anticipated viability of proximal and distal nerve segments will dictate whether or not an interposition graft can be used versus an alternate neural input such as a nerve transposition. Preoperative photos should be taken in order to document a visible deficit.

Surgical Considerations

Nerve composition may be variable even along the length of the same nerve, depending on the location.
Presence or absence of a nerve sheath or epineurium may require alternative techniques for nerve repair—that is, FN repair.
The proximal FN is devoid of a nerve sheath at the cerebellopontine angle. As the seventh cranial nerve travels through the temporal bone, it develops more of a covering. This nerve sheath offers some protection with surgical manipulation, thus allowing the extratemporal nerve to be more resilient to extensive dissection.
Epineurial repair is the standard technique of neurorrhaphy. Perineurial and endoneurial or fascicular repairs have been discussed; however, they have yet to prove beneficial.

Operative Period

Anesthesia

In the situation of early nerve repair where distal branches can be stimulated, the anesthesia team must be advised that no long-lasting paralytics should be administered.
Epinephrine 1:100,000 should be used without xylocaine if nerve stimulation will be necessary. Most operative suites will have 1:1000 epinephrine available. Dilution to 1:100,000 epinephrine is performed by mixing 0.1 mL 1:1000 epinephrine with 9.9 mL injectable saline for hemostasis without nerve inhibition.

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