Free Muscle Transfer for Long-Standing Facial Palsy

Abstract

Commonality to all patients with long-standing facial palsy is the inability to use the native mimetic muscles to restore motion since the motor end plates have undergone irreversible damage. Therefore, there is a need to insert a new neuromuscular unit, whether via a free or local functional muscle transfer. This chapter will discuss free functional muscle transfer.

Once the decision is made to use a free functional muscle transfer the next important factor is deciding on the donor nerve—the facial nerve or a non-facial nerve. The facial nerve can be used in two situations. The first and more common situation is using the contralateral normal facial nerve as a first stage cross facial nerve graft (CFNG). The second, less common scenario is the use of a proximal stump of the facial nerve to innervate the transplanted muscle if it exists.

Several situations exist when a donor facial nerve is not applicable or desired. These may include cases of bilateral facial palsy, older patients in which a CFNG often yields poor excursion, patients with disease entailing short-term prognosis, obese patients, or simply patients who prefer not waiting a prolonged period that is necessary in a two-stage procedure.

When using a cross facial nerve graft, several principles are important to follow. First, is to define what facial movement or mimetic muscle is the CFNG targeting, For example, is the CFNG targeting the smile (i.e. zygomaticus major muscle) or eye closure (i.e. orbicularis oculi muscle)? Most likely it is for reconstitution of the smile but often an additional nerve graft may be used for other purposes, for example, to assist in the blink. Once the goal is defined, selection of the appropriate donor nerve is performed after facial nerve mapping. This is done via nerve stimulation of select branches and identification of their exact function. The other extremely important criterion in selection is redundancy of nerve branches. Once a branch is selected it’s imperative that an additional branch that performs the same function is identified, thereby avoiding paralysis as a result of cutting the branch. It is extremely rare that a redundant branch is not identified. If that occurs avoiding cutting the branch is likely a safer approach.

In the two-stage approach a waiting period between 6 and 12 months is usually necessary for axonal growth through the nerve graft, depending on the length of the nerve graft. Clinically axonal growth is monitored by a Tinel Sign. At this time the second stage muscle transfer is planned. If a one stage approach is performed, no waiting period is necessary and the muscle is innervated with a non-facial nerve. Several potential muscles have been described and may be used. We use a partial gracilis muscle; however, latissimus dorsi, serratus, and pectoralis minor muscles have all been used and described. In common to all these muscles—they are transferred as a neuro-vascular-functional muscle unit.

This chapter discusses the principals of free muscle transfers for the restoration of midface reanimation with the use of either facial or non-facial nerves for neurotization.