Update - Surgical Management of the Marginal Mandibular Nerve Deficit

Richard L. Arden, M.D.

Isolated marginal mandibular nerve paralysis is a relatively common, yet frequently under-reported (1-3%), sequelae of surgical intervention involving the upper neck, salivary glands, or lateral mandible. The muscles innervated by the marginal branch include the depressor anguli oris (triangularis), depressor labii inferioris (quadratus), mentalis, a portion of the orbicularis oris, and in certain cases, the risorius and upper anterior portions of the platysma. Of these muscles, the greatest functional and aesthetic impact following loss of unilateral innervation occurs with the depressors anguli oris and labii inferioris. Failure of the depressor anguli oris to draw the corner of the mouth and lower lip downward and laterally, and of the depressor labii inferioris to draw the lip downward, laterally, and evert the vermillion border, yields the characteristic deformity. A hypotrophic, elevated, and inverted vermillion is seen best on opening the mouth, but typically remains well concealed in repose (inactive depressors) or lip-sealed smiling (dominant protagonist activity of elevators). When orbicularis oris muscle function is also compromised, difficultieswith puckering, purse-stringing, and oral competency may be seen. The goal, therefore, in surgical correction of the unilateral marginal nerve deficit, should be to restore lower lip position and symmetry (via eversion and depression), as well as sphincteric function (via tightening) when indicated.

Surgical Technique

With the patient in the upright position, an ideal inferolateral vector upon the paralytic lower lip is determined using an index finger with the patient in mid-and mouth excursion (Fig. 1 )

figure 1 - Desired position and inferior vector of lower lip depression is determined and marked with a skin scribe.

The point of static restraint, corresponding to subsequent sutures placement, typically lies 1.5 cm below the vermillion-cutaneous (V C) junction along this vector. A 1.2 cm incision is marked with its midpoint at the origin of this vector. Typically, this corresponds to a point approximately 1.5 cm medial to the oral commissure (Fig. 2).
figure 2 -A 1.2 cm incision at the V-C junction is centered about the predetermined vector, typically 1.5 cm medial to the oral commissure.

The patient is placed supine, and utilizing straight local or light local-sedation anesthesia, infiltration is performed conservatively from the V-C incision to the labiomental crease. It is imperative that the patient be alert enough to smile and open his/her mouth when prompted in order to assess the adequacy of repair. Following anesthetic and vasoconstrictive effect, the vermillion border incision is made down to the level of the orbicularis oris muscle. The lower skin flap is elevated inferiorly in a plane over this muscle to the labiomental crease. A permanent suture (4-0 Mersilene) is then used to vertically plicate the orbicularis oris muscle from 5 mm below the V-C junction to a point roughly 1 cm below this (Fig 3).
figure 3 - The orbicularis oris muscle is plicated over a 1 cm span along the vector following skin undermining.

The 5 mm inferior placement is necessary in order to avoid distortion of the vermillion. Suture placement is depicted diagrammatically in figure 4.
figure 4 - Elevated, inverted lip prior to correction (a); vertical plicaiton suture (b); resultant eversion and depression of lower lip after securing knot (c).

With the patient now sitting upright, the knot is gradually secured with the mouth open to judge the necessary endpoint. If over-or under-correction is present, the suture can be adjusted or removed and another placed. After adequate hemostasis is obtained, the vermillion incision is closed with several interrupted 5-0 nylon sutures. A representative case is depicted in figures 5 and 6.

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figure 5 - Preoperative right marginal mandibular nerve deficit.

figure 6 - Postoperative result at 4 months showing corrected deformity.

Discussion

Despite the myriad of surgical techniques available for the correction of the unilateral marginal mandibular nerve deformity, notable drawbacks are present in each. An idealized correction should afford simplicity of design, be reproducible, limit external scarring, restore lower lip symmetry and function, and be reversible. To date, a dynamic technique possessing these traits does not exist. Rather, the focus of attention has been on static correction of lower lip posture.

The technique described herein fulfills most of these requirements. Vertical suture plication literally takes 10 minutes to perform and could easily be done in an office setting. In our experience with 10 patients thus far, the results have been consistent and predictable. External scarring is limited to 1.2 cm and is well concealed within an anatomic junction line (vermillion border). Good lip depression and slight eversion is created by a static tension along the direction of pull of the depressor labii inferioris. This obviates the need for a more visible cheiloplasty incision. In concept, the results are similar to those described by Conley et al. with digastric transposition, but are achieved in a simpler, more aesthetic manner.

The major disadvantage of this procedure is that it will not improve functional competence of the oral sphincter in severe nerve dysfunction. In those selected cases where excessive hypotonicity of the orbicularis oris is present, this technique can be combined with lateral wedge resection. In the majority of marginal nerve palsies, however, correction of lower lip depression and eversion adequately addresses the deformity and has resulted in a high level of patient satisfaction.

Conclusion

We feel the technique of vertical suture plication adds to the armamentarium of surgical procedures that can be used to correct unilateral paralysis of the marginal branch of the facial nerve. The technique is simple to perform, yields predictable improvement, and results in negligible patient morbidity.

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