Abstract
Purpose
An asymmetric smile, caused by loss of function of the lip depressors, can be functionally and cosmetically debilitating. Although some surgeons report excellent results with muscle transfer to the lower lip, many facial reanimation surgeons find that dynamic techniques do not consistently address the lower lip. Our objectives were to retrospectively review our outcomes after treatment of the asymmetric lower lip, and to propose a progressive, stepwise algorithm for the management of lower lip asymmetry in facial paralysis.
Material/Methods
Retrospective chart review was performed on all patients treated in a multidisciplinary facial nerve center with lower lip asymmetry over an eighteen month period. Treatment ranged from a temporary trial of lidocaine, to chemodenervation with botulinum toxin, to pedicled digastric muscle transfer, and/or resection of the nonparetic depressor labii inferioris (DLI).
Results
Fifty-seven patients were treated with chemodenervation with botulinum toxin, four with anterior belly of the digastric transfer, and 3 with DLI resection. All patients with DLI resection had undergone chemodenervation to the contralateral lower lip with botulinum toxin and were pleased with the appearance of their smile.
Conclusions
We have found that lower lip asymmetry is optimally managed by adherence to a standardized protocol that offers patients insight into the likely outcome of chemodenervation or surgery and progresses systematically from the reversible to the irreversible. We present our algorithm for the management of the asymmetric lower lip, which reflects this graduated approach and has resulted in high patient satisfaction.
1
Introduction
Facial paralysis can create severe debilitation and social isolation. The inability to depress the lower lip, from either an isolated marginal mandibular nerve paralysis or a complete facial paralysis, significantly limits a patient’s ability to express a range of emotions. Patients with lower lip asymmetry are not able to depress, lateralize, or evert the lower lip, resulting in a smile pattern characterized by an elevated and inverted lower lip. Smile asymmetry is especially pronounced in patients with a “full denture” smile, in which all muscles are activated when smiling .
Techniques to manage the asymmetric lower lip revolve around either restoration of dynamic depressor muscle function on the paralyzed side or the weakening of functional side to improve symmetry . Methods that restore dynamic depressor muscle function have been reported in the literature, but require moderately involved surgical procedures under general anesthesia, and yield unpredictable results. Techniques that weaken the functional side, by chemodenervation with botulinum toxin or by depressor labii inferioris (DLI) resection, have been shown to be safe and effective office-based procedures, yielding high patient satisfaction . Despite this, patients with unilateral facial weakness are frequently psychologically unprepared for the suggestion that removal of additional facial movement might provide a benefit.
Many centers manage patients with lower lip asymmetry; however, in the current literature, a systematic management strategy, using a multitude of available techniques, does not exist. Herein, we describe our management of patients with lower lip asymmetry, and suggest an algorithm for the stepwise management of the asymmetric lower lip that we have found provides improved balance of the lower lip during facial expression, and higher patient satisfaction.
2
Anatomy
The depressor muscles of the lower lip include the DLI, the depressor anguli oris (DAO), and the platysma muscle . The mentalis muscle, located medial to this complex of muscles, acts as a lower lip elevator and everter. The DLI is the muscle most responsible for depression of the lower lip. It originates from the lower lateral surface of the body of the mandible, inferior to the mental foramen and inserts into the inferior and superficial surface of the orbicularis oris. At its origin, the DLI is 3 cm wide and covered laterally by the DAO for 1 to 2 cm, narrowing to 2 cm before insertion. The DLI everts the vermilion and depresses and lateralizes the lower lip. The DAO originates from the mandible, superficial to the DLI, and inserts onto the modiolus to depress the corner of the mouth. The platysma muscle plays a minor role in depressing the lip through its facial connections, although its resting tone can influence the resting, static position of the lower lip .
2
Anatomy
The depressor muscles of the lower lip include the DLI, the depressor anguli oris (DAO), and the platysma muscle . The mentalis muscle, located medial to this complex of muscles, acts as a lower lip elevator and everter. The DLI is the muscle most responsible for depression of the lower lip. It originates from the lower lateral surface of the body of the mandible, inferior to the mental foramen and inserts into the inferior and superficial surface of the orbicularis oris. At its origin, the DLI is 3 cm wide and covered laterally by the DAO for 1 to 2 cm, narrowing to 2 cm before insertion. The DLI everts the vermilion and depresses and lateralizes the lower lip. The DAO originates from the mandible, superficial to the DLI, and inserts onto the modiolus to depress the corner of the mouth. The platysma muscle plays a minor role in depressing the lip through its facial connections, although its resting tone can influence the resting, static position of the lower lip .
3
Patients and methods
A retrospective chart review was performed on all patients evaluated and treated in a multidisciplinary facial nerve center setting over an 18-month period who demonstrated lower lip asymmetry as a result of facial paralysis. Our stepwise clinical approach has evolved over the previous four years, and now begins with a one-time lidocaine injection to provide an immediate but short-lived visual sense of the potential effect of chemodenervation. If balance is improved and oral competence maintained, chemodeneravation with botulinum toxin is offered. During the study period, DLI division was offered in cases where repeat injections with botulinum toxin met with high satisfaction, and digastric transfer was offered in patients who categorically declined any “weakening” interventions or who were unhappy with the results of lower lip weakening. This study was approved by the institutional review board at the Massachusetts Eye and Ear Infirmary.
3.1
Technique for local anesthetic injection
The depressor labii inferioris muscle was identified by palpation of the lower lip, near the junction of the medial and lateral lower lip, while the patient was asked to fully animate his or her lip complex ( Fig. 1 ). The area of maximal resistance, noted as the examiner pushed up on the vermillon border, corresponded with the location of insertion of the DLI. The point of injection of local anesthesia was into the midsection of the muscle along its lateral border, to prevent inadvertent injection into the orbicularis oris muscle . The injections were performed in the office setting, with 2 mL of 1% lidocaine containing 1:100 000 epinephrine.
3.2
Technique for chemodenervation with botulinum toxin
If a patient was satisfied with the results of the motor blockade by injection with lidocaine, the patient was offered chemodenervation with botulinum toxin at the next clinic visit. The DLI muscle was identified in the same fashion as described for local anesthetic injection . Five units of botulinum toxin type A (100 U was mixed with 2 mL of normal saline creating a 5 U/.1 mL solution) was then injected into the midsection of the depressor labii inferioris muscle. Patients were seen in follow-up 2 to 3 weeks post injection to determine the success of the treatment. If the patient was satisfied with the results from chemodenervation, repeat injection was offered at 4- to 6-month intervals.
3.3
Technique for depressor labii inferioris division
Patients that continued to be satisfied with the results of chemodenervation after serial chemodenervation treatments were offered DLI resection ( Fig. 2 ). Ordinarily, DLI resection was performed in the clinic under local anesthesia. The lower lip was anesthetized with 1% lidocaine with 1:100 000 epinephrine. An incision was made in the mucosa of the right lower lip, approximately 1 cm below the margin of the lip. The fibers of the DLI were identified, and a 1 cm length of muscle was excised. The incision was closed in layers.
