When facial nerve dysfunction has exceeded 18 months, dynamic slings and free muscle transfers can be executed to restore facial and oral motor function. Severe neurofibrosis and myofibrosis in the distal neuromuscular unit preclude successful reinnervation. Patients with congenital facial paralyses cannot be reinnervated, since the neuromuscular units never developed. Regional muscle transposition and free-muscle transfer are the 2 modalities to reanimate the face in this subset of patients.
Regional muscle transfer can reanimate the lower third of the paralyzed face. This new neuromuscular unit is composed of the transferred muscle (to its new origin) with its original nerve and vascular supply.
The temporalis muscle may improve the symmetry of the commissure of the mouth and reestablish a voluntary smile. The vector of the temporalis muscle resembles that of the zygomaticus major and, thus, results in a lateral smile.
Temporalis muscle transposition can also reanimate the eyelids. Reanimation of the eye with the temporalis transfer can produce eyelid distortion. To avoid a contour defect, do not use the muscle anterior to the hairline. Transposition will not produce spontaneous mimetic function. Each movement necessitates a specific volitional action, in which the patient must consciously contract the transposed muscle in conjunction with the smiling. Reanimation of the eye with the temporalis muscle can cause eyelid distortion.
The muscle is harvested through a vertical incision in front of the ear that extends to the scalp. The middle section of the muscle and fascia is elevated and detached superiorly from the skull while preserving the inferior attachments. Two tongues are creating by bisecting the muscle, and the muscle is tunneled through a subcutaneous pocket from the zygomatic arch to the vermillion border. The ends of the temporalis are secured to the orbicularis and the corner of the mouth. The ends should be secured with enough tension to create some level of overcorrection. The patient initiates a smile by consciously tensing the temporalis muscle. Patients will require therapy to master this technique.
In his study, May reports improvement in 95% of patients with temporalis transfer for lower face reanimation and good-to-excellent results in 78% of patients. The complication rate was 18%; the most common complications were infection and implant-related complications. Other potential complications include failure of attachment, pulling away of the temporalis muscle from the commissure, and overcorrection of the upper lip. The transfer may also generate excess muscle bulk and a facial deformity, particularly over the zygoma.
The masseter muscle is another muscle used for reanimation of the commissure of the mouth, either alone or in conjunction with the temporalis. Unlike the temporalis, the vector of smile of the masseter muscle is in the buccinator-risorius direction, which produces a less natural smile. This muscle is elevated by detaching the anterior portion from its mandibular insertion. It is similarly bisected and secured to the modiolus. The muscle is quite bulky and can create facial irregularity or surface deformity, such as a bulge at the commissure. Postoperatively, patients must train the masseter with aggressive physical therapy to learn how to use the transposed masseter to produce a smile.
The smile is one of the most important facial expressions, and facial paralysis can debilitate an individual. Conley developed the modern method of transposing the tendon of the digastric muscle to the orbicularis of the lower lip. The blood supply and nerve to the anterior belly remains intact, and dynamic depression of the lower lip border is achieved. Of 36 patients treated in this manner by Conley, 33 were reported to have satisfactory results. This method is ideal for isolated palsy of the marginal mandibular nerve only, since it can create oral incompetence in patients with more extensive palsy of the lower face.
Depressor muscle function is important to dentured smile as well as to expressions of sadness, anger, and sorrow. The lower lip is animated by interactions of the orbicularis ori, depressor labii inferioris, depressor anguli oris, mentalis, and platysma. Terzis describes a technique to improve this type of smile by transfer either of the anterior belly of the digastric tenor or of the platysma. Other authors argue that this symmetrical smile could be achieved with less invasive approaches, including BOTOX® injections or myectomy of the depressor labii inferioris.
Regional muscle transposition is limited by anatomic constraints of size and vectors and often produces results slightly better than static strategies. Regional muscle procedures are appropriate in patients who are in poor health or who will not survive beyond the 12-24 month period of neurotization of a free muscle transfer. Such procedures provide immediate reanimation and are technically less demanding than cross-facial nerve grafting with free muscle transfer.
Principles of Free-Muscle Transfer
Cross-facial nerve grafting with microneurovascular muscle transfer is the best strategy for facial reanimation when a patient has long-established facial paralysis (>24 mo). Other approaches leave residual asymmetry, an unnatural appearance, and unwanted facial movements while eating. The advent of microsurgical technique and free-muscle transfer ignited a new epoch for facial reconstruction in patients with chronic facial palsy. Free-muscle transfer supplies a new neuromuscular unit to the face via a free-muscle flap and a grafted donor cranial nerve, usually a cross-facial nerve graft. This modality establishes more precise vectors in addition to spontaneous mimetic facial expression. Most commonly, the surgeon executes a 2-stage technique of cross-facial nerve graft followed by a delayed free-muscle transfer. The rationale for the delay is to prevent atrophy of the muscle graft while waiting for axons to travel the length of the nerve graft.
Cross-facial nerve graft
Occasionally, the proximal segment of the ipsilateral facial nerve is available for grafting to innervate a free-muscle transfer. This situation most commonly occurs in the event of a failed interposition nerve graft, resulting in facial musculature that no longer can be reinnervated.
The contralateral facial nerve is chosen as the donor nerve, and a redundant zygomaticus branch is selected for grafting. The hypoglossal nerve also can act as a donor, either by a direct or jump graft alone or in conjunction with a cross-facial graft. The sural nerve is anastomosed to the contralateral facial nerve or substituted cranial nerve and tunneled subcutaneously from the donor nerve to the planned site of free-muscle transfer and the distal segment of the graft is tagged. The ideal time for the muscle transfer occurs when a Tinel sign is detected in the distal nerve end, indicating completion of axon growth.
Muscles suitable for transfer
Free-muscle transfer is usually performed 9-12 months after nerve graft. A plethora of muscles have been assiduously investigated for free transfer to the paralyzed face, including the gracilis, serratus, pectoralis minor, latissimus dorsi, platysma, rectus abdominis, rectus femoris, and extensor digitorum brevis.
The original report by Harii in 1976 of free-muscle transfer for facial paralysis described use of the gracilis muscle. It remains the muscle of choice because of its relative ease of dissection, adequate neurovascular pedicle, and muscle fiber length, which corresponds to the action of the zygomaticus major muscle. The vascular pedicle is derived from the medial femoral circumflex artery and provides up to 8 cm of length. Innervation of the gracilis is provided by the anterior branch of the obturator nerve, which can be dissected to a length of 10-12 cm.
During the second-stage procedure, the surgeon must identify the distal end of the nerve graft and send a frozen section for confirmation of viable axons. The muscle flap is harvested and transferred to the face. The flap is secured to the periosteum of the zygomatic arch and the modiolus in a vector that corresponds to the smile on the contralateral face. Subsequently, the microanastomosis between the flap and recipient vessels is executed, followed by the nerve anastomosis as close to the muscle as possible. Movement can be expected in 6-9 months, with improvement over the following 2-3 years.
Lifchez and Gasparri endorse the serratus anterior for free-muscle transfer based on their anatomical findings. Each serratus slip, divided along fascial planes, can generate a distinct force vector for facial reanimation with a total of 5 slips and 10 subslips. This serratus anterior can, therefore, be used as a single donor muscle with multiple vectors of action and multiple functions (eg, restoration of a symmetric smile with simultaneous but independent eyelid closure).
Terzis and Noah found no significant effect of age, gender, or ischemia time on outcome in their series of 100 free-muscle transfers. They report moderate or better results in 80% of patients undergoing free-muscle transfer, based on a 5-step scale of judgment. O’Brien et al report good-to-excellent results in 51% of 47 patients treated by microvascular free-muscle transfer; the surgeons most commonly used cross-facial nerve grafts and gracilis muscle transfers in their technique.
One-stage free muscle transfer
In their study of 25 patients, Kumar and Hassan compared single-stage versus dual-stage free tissue transfer for facial reconstruction. The gracilis obdurator nerve branch can yield a length of 12 cm, which allows primary anastamosis of this nerve to the contralateral facial nerve. However, this technique produces an additional scar on the cheek. The single-stage transfer has fewer complications and a reduced recovery time with decreased rehabilitation, but the dual-stage approach has overall better symmetry.
In their investigation of 166 free gracilis transfers, Manktelow and Zuker explored muscle transfer with cross-facial nerve graft versus single-stage transfer to the masseter nerve. The excursion of the free gracilis innervated by the masseter nerves is greater than that of the cross-facial nerve graft. This is probably attributable to the different motor nerve used to reinnervate the muscle. The cross-face nerve graft provides improved spontaneity in terms of movement, which is vital to a normal smile in children. This is a more important characteristic than degree of excursion. Their future studies will explore the nature of spontaneity in their muscle transfers utilizing the masseter nerve as a donor.
Although use of the masseter nerve with free tissue transfer was previously explored and considered only in the setting of M ö bius syndrome, bilateral facial paralysis, and facial paralysis not suitable for cross-facial nerve grafting, the masseter nerve’s applicability and role has been recently extended to patients with unilateral facial palsy. This one-stage strategy, incorporating the masseter nerve with free tissue transfer, has become a reasonable alternative (and may become the criterion standard) to the dual-stage approach with cross-facial nerve grafting. The enormous advantage of the masseter nerve-free tissue transfer technique is that, unlike the cross-facial nerve, the masseter nerve donor produces a movement and muscle excursion (in relation to smile and commissure excursion) in normal range with consistent movement. Also, this technique obviates the need for a second operation.