Reanimation of Mouth Corner with Free Gracilis Muscle Flap

Abstract

Gracilis muscle is the most commonly used muscle in facial paralysis. Although the use of the contralateral buccal branches with the sural nerve graft as the recipient nerve provides spontaneous smiling, the main disadvantage is the weak contraction due to insufficient muscle innervation. Although the masseter nerve is a chewing muscle, it can be used as a recipient nerve to provide a strong contraction. However, postoperative adaptation of the brain is required to ensure spontaneous smiling. In this article, I will evaluate the results of the postoperative third-year results of 11 patients with partial thickness gracilis muscle. I carried on the masseter recipient nerve for oral corner reanimation in facial paralysis.

1. Introduction

In complete facial paralysis, the effected parts of the patients’ face are frontalis muscle, muscles of facial expressions, and platysma muscle in the neck. The inability that troubles patients the most is the paralysis of the muscles on the effected side that pull the mouth corner vectorally outward from the center of the face during the act of smiling. Zygomaticus major muscle and minor muscle, which pull the upper lip upward and which are the main muscles that function during smiling, combined with rhisorius muscle, which pull the side of the lip outward, create the function of smiling. In a study it has been found that children smile 400 times and adults smile 20 times in a day and the importance of the action of smiling in people’s lives in introducing themselves to their social environment has been shown [1]. In unilateral facial paralysis, an asymmetrical view is formed during smiling due to the lack of function in the muscles described above and in bilateral facial paralysis (Moebius syndrome, etc.), a motionless face is formed, which causes an apathic face appearance. Attempts on gaining the function of smiling constitute the main basis in facial reanimation operations, which are operations that aim to recreate the function of the effected muscles in cases of facial paralysis. Attempts on the muscles that close the eyelids are the second most frequent operations. Functional muscle transfer is done in attempts to recreate function of smiling. In this article, I am going to mention my experiences on single session gracilis muscle transfer in which masseter nerve is used as the recipient nerve.

2. Materials and method

In this study, 11 patients of at least 3 years of follow-up (between 2011 and 2019) are included. Following preauricular incision, a pouch is created by lifting the skin flap at the mouth corner upward and downward. After the outer edge of masseter muscle is found and after a back parallel line is drawn starting from 1 to 1.5 cm away from the zygomatic arch, a point is marked on that line 3–3.5 cm away from tragus. Masseter nerve is found by parallel dissection to muscle fibers between superficial and deep lobes of masseter muscle, approximately at 1.5 cm deep of superficial musculoaponeurotic system (SMAS) [2]. Nerve is dissected at its full length, the branch that goes to deep lobe is preserved, and the superficial branch is determined as the recipient nerve. On inner side of the thigh, adductor longus muscle is palpated, a parallel incision to that muscle is made, and gracilis muscle is found positioned medially to adductor longus muscle (Figure 1). After dissection of the pedicle, markings on the muscle, 3 cm apart from each other, are made with absorbable sutures, which are going to define the entrance site of the central predicle (Figure 2). Branch of the obturator nerve to gracilis muscle is tracked to the site of origin from the main nerve body. About 1/3–2/3 anterior segment of the muscle, 2–3 cm longer than the distance between zygomatic arch and mouth corner, is taken using a straight intestinal stapler (Figure 3). The size of the segment that is going to be used is determined according to the entrance site of the pedicle on the muscle. First of all, to technically facilitate the procedure, nerve of the gracilis muscle flap is repaired and sutured to the recipient masseter nerve. Then, flap is transferred to facial artery and vein, which had been prepared as recipient vessels. Upper end of the muscle is sutured to zygomatic arch with 2/0 Polydioxanone (PDS). Distal end of the muscle is divided in three parts: upper part is sutured to the upper side of the lip and to the base of nose, lower part is sutured to the side of the lower lip, and middle part is sutured to the mouth corner. After the operation, patient’s mouth corner is sutured as a static strap, in a position that muscles stay tight and constricted, symmetrical to the contralateral side. A drain is placed next to the pedicle, without completely closing the preauricular incision, bleeding control on the end of the muscle and circulatory control with Doppler Ultrasound are performed. Patients are immobilized for 5 days in bed. No anticoagulants were used and only be used local heating with floor lamp. After day 5, with observation of normal circulation following mobilization, preauricular incision is closed. Average time that patients start to feel the first muscle contractions is observed to be around 2 months. After contractions begin, Transcutaneous Electrical Nerve Stimulation (TENS) device is used on patients for 20 minutes four times in a day. The traction of the mouth corner is started to be observed around 6–8 months on average. Patients’ muscle power being increased, maximum muscle strength is achieved approximately 1.5–2 years on average. After patients start to pull the lip corner, physiotherapy is started. Advices of practicing control on smiling movements with a mirror, guidance on patients’ social lives, which may lead to all day smiling, and advice of watching a comedy movie every other day were made to patients.

Figure 1.

View of the gracilis muscle and its pedicle drawn on skin.

Figure 2.

Gracilis free muscle flap marked at 3 cm intervals.

Figure 3.

Removal of the muscle flap with straight intestinal stapler.

3. Results

Pictures of patients were taken after patients were informed about their pictures were to be used and published in scientific papers. Verbal and written consent has been acquired from patients regarding the use of their pictures in publications. No flap loss is observed. On eight of the patients, symmetrical smiling to the contralateral side is observed (Figures 4 and 5), on two of the patients, a pull 1–1.5 cm less than the contralateral side is observed. However, because of patient satisfaction, no muscle plication attempts aiming augmentation of traction of the lip corner were made. A swollen appearance on the face is observed on six of the patients due to muscles; however, since patients are still on follow-up period, a flap thinning procedure has not been performed.

Figure 4.

Preoperative view of the patient.

Figure 5.

View of the patient 8 years after the operation.

4. Discussion

Although the most common choice is use of gracilis muscle in reanimation of smiling muscles in facial paralysis [3], free muscle transfers such as serratus anterior muscle, latissimus dorsi muscle, extensor digitorum brevis muscle, and pedicled muscle transfers such as temporalis muscle transfers have been used.

In free muscle transfers, the contralateral facial nerve with use of nerve grafts, ipsilateral hypoglossal nerve (12th Cranial Nerve (CN)), ipsilateral accessory nerve (11th CN), or the ipsilateral masseter nerve, which is one of the motor branches of fifth CN, can be used as the recipient nerves. In the cases where the contralateral facial nerve is used as the recipient nerve, when an impulse is generated toward the contralateral side, it passes on the nerve graft and causes contraction of the transferred muscle, which in the end causes a “spontaneous smile” on the effected side. This situation is not possible in cases where other cranial nerves except facial nerve on the same side are used as the recipient nerve. In the beginning of cases, which are used CV as recipient nerve, in order to generate smiling function on the operated side, the patient needs to think of an action, which will cause their chewing muscles to work. In the studies carried out, it has been shown that masticatory center and smiling center in the brain are located close to each other and with certain exercises accessory neural pathways will be generated between these two centers [4]. Therefore, it has been stated that smiling function will be performed with use of these pathways when patients want to smile. Some studies state that simultaneous stimulation of masticatory center causes action on transferred muscle to generate smiling action, during the stimulation of the smiling center. It has been stated that success of the operation is increased with younger patient. When transfer to the masseter nerve operations is performed on patients who were in childhood, spontaneous smiling is achieved at advanced ages approximately 80% of the patients, compared with 50–80% of the patients when the operation is done in older ages [5, 6]. There are important exercises that the patient and the physiotherapist need to perform in order the neural pathways to be created. Patients are advised to smile constantly in their social lives. This includes daily life advices from greeting everyone in the most appropriate way to social lives, to trying to use every opportunity throughout the day to smile. Patients are advised to watch a comedy movie on alternate days. Furthermore, one of the most important practices is exercises to be done in front of a mirror. The goal of these exercises is to increase patients’ comprehension of the traction strength on the transferred side during smiling and to equalize their smile with the contralateral side. Therefore, patients are going to make their brains learn the traction power of the transferred muscle, and they are going to equalize the strength on both sides of their face during smiling. To start these exercises, it is necessary to wait until the maximum traction strength of the transferred muscle is achieved and revision operations regarding muscle traction and tension are completed. On my cases, I start external electrical stimulus by using TENS devices when patients feel the first contraction on the transferred muscle, although a clinically visible contraction has not been achieved. I suggest these external stimuli are given in 20 minute sessions every 3 hours. Therefore, I believe that the number of new neuromuscular junctions is increased and direct muscle stimulation is provided during muscle innervation period, which prevents muscle atrophy. There is a direct proportion between the number of neurons in the recipient nerve and contraction strength of transferred muscle. With increased number of neurons in the recipient nerve, the number of neurons, which reach the transferred muscle and cause contraction, is increased. In valuable studies carried out, it is stated that buccal branch of the facial nerve contains approximately 834+/−285 neurons. When these neurons are used at the paralyzed side with a sural nerve graft, the axons budded from the recipient nerve need to pass through two nerve coaptation sites through the nerve graft. In studies carried out, number of the neurons of buccal nerve is observed to be around 100–200 after these neurons pass through the nerve graft and reach the transferred muscle. This situation is because number of neurons of the recipient nerve is few and because neurons pass through two coaptation sites. The branch of the masseter nerve that is used as the recipient nerve contains 1542+/−291 neurons [2, 7], which is much greater than buccal branch of the facial nerve. Other benefit of using the masseter nerve is, since neurons are going to pass through a single nerve coaptation site, the decrease in the number of neurons that reach the transferred muscle is going to be less compared with when buccal branch is used as the recipient nerve. In a study, it is shown that the number of neurons pass to the obturatory nerve from masseter nerve is 10–15 times greater than the neurons pass through sural nerve graft. In my clinical practice, in the beginning I used buccal branches as the recipient nerves. However, because I observed muscle traction strength was fairly weak and because a second session was needed, I have started to transfer partial thickness gracilis muscle to the masseter nerve as the recipient nerve with a single session operation. The second frequent complaint of patients who had free muscle transfer is the unaesthetic view of the patients’ faces during contraction caused by excessive swelling, following the most common complaints, which are about traction strength [8]. This is the reason during removal of the flap from donor site, I use 1/3–2/3 of the muscle according to entrance site of the pedicle8. I use straight intestinal staplers to remove the muscle flap to be transferred from the main muscle. Therefore, ends of the muscle flap stay together preventing separation of fibers at the ends of the flap. These titanium staplers facilitate fixation of proximal end of the flap to zygomatic arch and by preventing fibers from scattering staplers facilitate division of the distal end to three parts, one for upper lip, one for lower lip, and one for mouth corner. Therefore, fixation of muscle fibers to sides of lips and mouth corner, which is among the most important parts of the operation, can easily be done with the help of staplers. I suggest that if a flap thinning operation is being planned, it should be performed at late stages after the operation. Because I believe in the long terms if the muscle is fixated to the recipient site properly and soundly, it adapts well and a thinning operation is not going to be necessary. I believe that most of the permanent swellings during muscle contraction are caused by poor fixation of the muscle to lip corner or to the zygomatic arch or detachment of the muscle from fixation sites because of poor wound healing or weak adhesion of the muscle. However, if none of the problems stated above exists and swelling during contraction is observable, a thinning operation to the nearest parts of the muscle to the skin can be performed very carefully. It has to be kept in mind that as a result of a careless procedure, contractions of the transferred muscle can be totally lost.

5. Conclusions

As a result, I believe reanimation of smiling function in facial paralysis with one session partial thickness free gracilis muscle flap with the masseter nerve as the recipient nerve is superior to other techniques despite some disadvantages regarding spontaneous smiling.

Conflict of interest

The authors declare no conflict of interest.