The use of the masseteric nerve as donor nerve represents a single-stage alternative to the criterion standard two-stage procedure of cross-facial nerve grafting and free muscle transfer in facial paralysis. We provide a detailed description to safely perform this technique with a gracilis muscle transfer and discuss indications and limitations.
Unilateral facial paralysis is a common disease that is associated with significant functional, aesthetic and psychological issues. Though idiopathic facial paralysis (Bell’s palsy) is the most common diagnosis, patients can also present with a history of physical trauma, infectious disease, tumor, or iatrogenic facial paralysis. Early repair within one year of injury can be achieved by direct nerve repair, cross-face nerve grafting or regional nerve transfer. It is due to muscle atrophy that in long lasting facial paralysis complex reconstructive methods have to be applied. Instead of one single procedure, different surgical approaches have to be considered to alleviate the various components of the paralysis.
The reconstruction of a spontaneous dynamic smile with a symmetric resting tone is a crucial factor to overcome the functional deficits and the social handicap that are associated with facial paralysis. Although numerous surgical techniques have been described, a two-stage approach with an initial cross-facial nerve grafting followed by a free functional muscle transfer is most frequently applied. In selected patients however, a single-stage reconstruction using the motor nerve to the masseter as donor nerve is superior to a two-stage repair. The gracilis muscle is most commonly used for reconstruction, as it presents with a constant anatomy, a simple dissection and minimal donor site morbidity.
Here we demonstrate the pre-operative work-up, the post-operative management, and precisely describe the surgical procedure of single-stage microsurgical reconstruction of the smile by free functional gracilis muscle transfer in a step by step protocol. We further illustrate common pitfalls and provide useful tips which should enable the reader to truly comprehend the procedure. We further discuss indications and limitations of the technique and demonstrate representative results.
The facial nerve is involved in ocular protection, articulation, oral continence and greatly affects the aesthetic appearance of the face. Impairment of this nerve is therefore associated with significant morbidity and social withdrawal. Despite significant advances in therapy, the multitude of problems associated with the paralyzed face can only be targeted with a broad spectrum of additional procedures. Common to all surgical techniques is the need for an exact anatomical knowledge.
Facial nerve anatomy
The facial nerve consists of a branchial motor component for voluntary motor control of the facial musculature and a visceral motor component for parasympathetic control of lacrimal, submandibular, and sublingual glands. Besides, there are two sensory components for the innervation of the external auditory canal and for the taste in the anterior two third of the tongue. The course of the facial nerve can be subdivided into three segments: intracranial, intratemporal, and extratemporal. In the intracranial segment, the upper group of neurons that innervate the frontalis muscle and the periauricular region receives bilateral cortical input. Neurons that innervate the remaining facial muscles receive contralateral cortical input exclusively. As a consequence, frontalis function is maintained in ipsilateral supranuclear lesions. The intratemporal segment can be further divided into three segments. In the labyrinthine segment, the greater petrosal nerve leaves the trunk to supply the lacrimal gland with parasympathetic fibers1.
In the mastoid segment, the thin stapedius nerve runs to the correspondent muscle. Parasympathetic branches innervate the submandibular, sublingual and anterior lingual glands, whereas the anterior two thirds of the tongue are supplied with gustatory fibres (chorda tympani). The main stem of the facial nerve exits the bony canal through the stylomastoid foramen. This is the beginning of the extratemporal segment, however arborisation does not start before entering the parotid gland. The nerve is first divided into 3 to 4 motor divisions that form the intraparotid plexus and ultimately give rise to the temporal, zygomatic, buccal, mandibular and cervical branches2.
Differential diagnosis of facial paralysis
As etiology of facial paralysis is broad and hard to classify, the division that is affected should be considered first.
Intracranial facial paralysis can be caused by lacunar infarcts or tumors of the intracranial cavity. Bacterial and viral infections, cholesteatoma and Bell’s palsy can be reasons for intratemporal nerve damage. Neoplastic malignancies and associated surgical therapy are the dominant causes for extratemporal facial paralysis. Although Bell’s palsy represents the most common diagnosis in patients with facial paralysis, most patients recover completely without sequelae and do not need surgery3. The second most common cause of facial paralysis is trauma. Here, fractures to the temporal bone are the predominant trauma mechanism4.
Treatment types of facial paralysis
Numerous surgical options exist for the treatment of facial paralysis and they may be classified into reinnervation, static reconstruction and dynamic reconstruction. Typically, two years are considered to be the time from injury in which function after reinnervation can be regained satisfactory with reinnervating procedures5. Later on, denervation atrophy of facial muscles precludes their usefulness for further reconstruction. Reinnervation can be obtained by primary nerve repair, interpositional nerve grafts, cross-facial nerve grafting or cranial nerve transfer. Static reconstruction techniques are directed to correct functional disabilities, (protection of the cornea, improvement of nasal airflow, and prevention of drooling) and to improve symmetry at rest. Typical procedures are browlift for brow ptosis, or canthoplasty for lower lid ectropion. Static reconstruction is preferred in elderly patients with significant comorbidities or in massive facial defects secondary to trauma or cancer resection.
The surgical techniques of dynamic reconstruction can be subdivided into regional muscle transfer and free microneurovascular muscle transfer with either coaptation to the masseter motor branch or cross-facial nerve grafting. The latter represents the criterion standard for the reconstruction of the smile in facial paralysis, as no other treatment option reliably achieves a spontaneous smile that is crucial to improve social handicap. Coaptation to the masseter motor branch is the treatment modality of choice for patients with bilateral paralysis, however indications have extended, as elderly patients or patients with significant comorbidities usually prefer a single-stage procedure6.
Gracilis flap
Regional anatomy
The gracilis muscle is a rather superficial muscle of the medial thigh, representing the longest muscle of the adductor muscles. It originates from the lower symphysis and the inferior ramus of the pubis. Running distally, the muscle becomes narrow and inserts distal to the knee joint on the tibia that allows not only adduction of the thigh but also flexion of the knee. The gracilis muscle has a type II circulatory pattern after Mathes and Nahai with an arterial supply from a dominant and some minor vascular pedicles7. The dominant artery exits the muscle at the hilum to course laterally and usually terminates in the medial circumflex artery. Rarely, the dominant artery terminates directly in the deep femoral artery. Venous supply of the gracilis muscle is usually achieved through two venae comitantes, that course deep to the adductor longus muscle to follow the dominant artery. Innervation of the muscle is achieved through an anterior branch of the obturator nerve that enters the muscle 1-2 cm superiorly to the hilum.
Clinical use
The gracilis muscle is a valuable donor muscle for reconstructive microsurgery and has become the muscle of choice for many surgeons for functional free muscle transfer. This is owed to the fact that there is little donor site morbidity and the flap shows optimal proportions with regards to excursion of the muscle and vascular pedicle dimensions respectively. A long single innervated motor nerve alleviates functional flap harvest8.
We here demonstrate the case of a 49 year old female, who initially presented with a complete picture of left peripheral facial paralysis following resection of an acoustic neuroma (vestibular schwannoma) 2 years earlier. The patient was most afflicted by facial asymmetry, particularly when smiling. Other pre-existing comorbidities were not documented.
Upon clinical examination, the patient showed a complete paresis of the frontalis muscle, however a satisfactory forehead symmetry at rest. Lid closure was insufficient on the left with a lagophthalmos of 5 mm and Bell’s phenomenon. Signs of cornea irritation and ectropion were absent. At rest, the patient showed a moderate asymmetry of the corner of the mouth with a tragus-modiolus distance of 11 cm on the right and 11.5 cm on the left at rest. Upon smiling, tragus-modiolus distance scaled down to 9 cm on the right and elongated on the left to 12 cm. After extensive counseling, the patient wished for a single-staged dynamic reconstruction of the smile with a free functional gracilis transfer using the masseter as donor nerve. The patient was also informed about various techniques of lid closure reconstruction, however declined surgical treatment at this stage. The course of the treatment was uncomplicated. Signs of reinnervation were first noticed three month postoperatively. Four months after surgery, the patient presented with unremarkable scarring along the former modified facelift incision line. Symmetry at rest and deliberate smiling were excellent with a satisfactory definition of the nasolabial crease. The patient also showed a completely spontaneous smile. Pre- and 9-month postoperative range of excursion of the corner of the mouth was documented by videography.
NOTE: The Patient shown in the video has agreed on publication of the video material. Written consent was obtained. The protocol follows the guidelines of the human research ethics committee of the University of Freiburg. Though surgeons may have different preferences, the following protocol will focus on the authors’ preferred technique.
1. Pre-operative Workup
2. Facial Preparation
NOTE: Perform the procedure with a two team approach. Here, surgical steps are described one after another.
3. Flap Harvest
NOTE: The gracilis flap is harvested simultaneously with the facial dissection.
4. Flap Insertion
5. Postoperative Treatment and Follow-up
The use of the masseteric nerve for reinnervation of the muscle graft was assessed in 5 patients (Table 1). Among them, acoustic neuroma resection was the main cause for facial paralysis. 3 candidates preferred the single-stage procedure rather than the “gold standard” two-stage approach. In two patients, the procedure served as a rescue procedure after insufficient stimulation by the cross-facial nerve graft (CFNG).
Reinnervation of the gracilis flap after single-stage repair was detectable within 3 months. Oral commissure excursion was satisfactory in all patients (Figure 1) however a spontaneous smile could only be achieved in one patient and occasionally in two patients. Secondary thinning of the flap was necessary in three patients.
Representative results are shown within the video.
Figure 1: Post-operative evaluation of the distance between the tragus and the oral commissure (T-C) at rest and under maximal excursion of the oral commissure. Values are in % of the healthy side at rest (n = 5). The use of the masseteric nerve for reinnervation of the muscle graft provides a strong excursion of the oral commissure with a symmetrical result when compared to the healthy side (ns= not significant).
Table 1: Patient demographics.
Even though different surgical techniques have been described to regain a dynamic smile in patients with long standing facial paralysis, the two-stage repair with initial cross facial nerve grafting and consecutive free gracilis muscle transfer is seen as the “criterion standard”.
Although a two-stage procedure, the technique allows for spontaneity of the smile which is seen as a crucial factor to overcome the social handicap associated with facial palsy13.In cases of bilateral facial paralysis and Möbius syndrome, the concept of muscle transplantation in the absence of the seventh nerve can be applied. Here, the masseter nerve as a branch of the trigeminal (fifth nerve) has increasingly been recommended to power the free muscle flap. As elderly patients or patients with significant morbidity tend to prefer a single-stage procedure, indications of the masseteric coaptation have significantly been expanded during the last years14.
There are clearly several advantages of masserteric nerve grafting. Apart from secondary thinning of the flap that is necessary in some patients, using the masseteric nerve is a single-stage procedure that preserves the contralateral healthy facial nerve and allows for a greater axonal load that is delivered to the flap. Conversely, incomplete reinnervation and partial muscle atrophy is often seen after facial nerve grafting, as less than 50% of axons cross the nerve graft15,16. Using the masseteric nerve results in a greater excursion of the oral commissure when compared to coaptation of the neural pedicle of the muscle flap to a cross-face nerve graft and consequently might be the method of choice in patients with a strong contralateral smile where cross-face nerve grafting is insufficient to restore symmetry14. Therefore the masseteric nerve can also be used to innervate a gracilis muscle flap in a secondary procedure when a gracilis muscle flap primarily innervated by a CFNG does not show sufficient muscle excursion to achieve a symmetric smile17. As a result of the strong neural input and minimal atrophy of the muscle, thinning out of the flap may become necessary in some patients that then require a minor secondary procedure.
In some patients, single-stage reanimation of the smile powered by the masseteric nerve does not provide spontaneous activity. The smile movement must be learned as part of a conscious effort. However, spontaneity can be observed in about two thirds of the cases which is also confirmed by our own observations18. To date, the determinants of achieving a spontaneous smile after masseteric reinnervation are unknown, though the parallel innervation of the masseter muscle upon smiling that is seen in about two thirds of the population or alternatively, a degree of cortical plasticity that develops following a program of biofeedback exercises have been proposed19,20. Further research is needed to specify the determinants of achieving a spontaneous smile in the future in order to provide the patient with an individualized treatment plan.We believe that once clear predictions can be made on whether the patient will achieve a spontaneous smile with this single stage procedure we might see a change in paradigm regarding reanimation of the face as in these patients a masseteric nerve coaptation could be preferable to a CFNG coaptation.
Crucial to success is the surgery of the recipient vessels and nerve, as well as the meticulous preparation of the gracilis muscle. Even though most plastic surgeons should be familiar with the raising of the gracilis muscle as a free flap the situation in this context is more demanding. The segmental harvest of the muscle is challenging, as the neural supply has to be maintained. When separating the muscle segment the usefulness of a neural stimulator cannot be emphasized enough. The repetitive control during dissection that the harvested segment still responds by contraction to stimulation of the neural pedicle ensures that no intramuscular branches have been dissected. If unexpectedly the gracilis muscle cannot be harvested or does not seem to be suitable for free flap transfer the adductor magnus muscle can be raised instead as a salvage procedure21.If patients cannot or do not want to undergo microsurgical reconstruction, we usually choose local muscle transfers that can achieve good outcomes but are generally regarded as second choice to free flap transfers22. After microsurgical gracilis muscle transfer, we strongly recommend the use of an implantable doppler probe as this allows for a continuous monitoring of flap perfusion. Though controversy exists in the use implantable dopplers, our own data showed a revision success rate of 75 to 90% that proves that the system is efficient enough in daily use23.
In conclusion dynamic reanimation of the smile remains to be of one of most demanding areas in plastic surgery. Under the multitude of surgical techniques, we here describe pre- and postoperative workup of the single-stage reconstruction utilizing the motor nerve to the masseter and precisely elucidate every single surgical step. We emphasize the importance of a thorough pre-operative patient counseling, as this will significantly affect patient satisfaction. We illustrate the atraumatic preparation of facial vessels and the masseter nerve in a step-by-step fashion. The elevation of the gracilis flap should be a standard procedure to every plastic surgeon. For functional muscle transfer however, there are certain features to be considered in order to gain ideal functional flap dimensions. Finally, we emphasize the importance of flap positioning and application of initial tension for achieving a natural symmetrical smile.
The authors have nothing to disclose.
Dr. Eisenhardt is funded by the German Research Foundation (DFG) # EI 866/1-1 and #EI 866/2-1.
Name of Material/ Equipment | Company | Catalog Number | Comments/Description |
Nylon Suture, 9-0 | Serag Weissner | Z0039490 | ° |
Polypropylene Suture | Ethicon | – | Multiple thread sizes |
Suprarenin 1mg/ml | Sanofi | – | ° |
Cook-Swartz Doppler Probe | Cook Medical | G03014 | ° |
DP-M350 Blood Flow Monitor | Cook Medical | – | ° |
Surgical Microscope OPMI Vario | Carl Zeiss | – | ° |
Microsurgical instruments lab set | S&T | 767 | ° |
Biemer vessel clip | Diener | 64,562 | ° |
Applying forceps | Diener | 64,568 | for Biemer vessel clip |
Cefuroxim 1500mg | Fresenius | J01DC02 | ° |
Braunoderm | Braun Melsungen | 3881105 | ° |
Octenisept | Schuelke & Mayr | 5702764 | ° |
ISIS Neuromonitoring System | Inomed | – | ° |
Tissucol | Baxter | 1.33052E+12 | Fibrin glue |
Jackson-Pratt Wound Drainage | Medline | SU130-1060 | |
Myacyne Ointment | Schur Pharma | – |