Introduction

The cervicomental angle and the contours of the neck are very important determinants of facial aesthetics and are readily modified in facial rejuvenative surgery. Deep plane procedures in the neck are often required to reach the aesthetic endpoint of a defined, less obtuse cervicomental angle and smooth surface contours. Four structures are altered in deep plane procedures of the neck: the platysma, subplatysmal fat, the anterior belly of the digastric muscle, and the submandibular gland. Deep plane procedures involving these structures are most effective when employed in concert with other rejuvenation efforts in the superficial structures of the neck and the remainder of the face. With that in mind, this chapter focuses on deep plane procedures and how they are integrated into a global approach to cervicofacial rejuvenation.

History

Skoog was one of the first surgeons to advocate deep plane dissection in facial rejuvenation surgery. Mitz and Pyronie characterized the SMAS and identified its continuity with the plastysma, the major investing supportive structure of the neck. Based on this anatomy, Hamra, Owsley, Connell, Aston and others have advocated raising the platysma as a continuous flap with the SMAS of the face, with or without elevation of the overlying skin in a separate plane of dissection.

Aston described the eight most common platysmal deformities and Ellenbogen established visual criteria for the successful rejuvenation of the neck. De Souza Pinto, Souther and later Feldman demonstrated the importance of midline tightening of the plastysma. Connell advocated low myotomy to treat a short platysma, one of the etiologic factors causing an obtuse cervicomental angle, and to treat platysmal bands. Furthermore, Connell popularized medial platysmal elevation for access to the submental and submandibular deep structures and advocated resection, total or subtotal, of the anterior belly of digastric muscle. Guyuron observed that this resection results in retropositioning of the hyoid bone and thus favorable deepening of the cervicomental angle. De Pina and Connell discussed resection of the submandibular gland and Guerrerosantos and Feldman have discussed suspension of the gland.

Physical evaluation

Fig. 20.1 Lateral view of the cervical region in a patient with an obtuse cervicomental angle.

Fig. 20.2 Physical exam. The upper figure demonstrates a patient at rest to show excess skin.

Fig. 20.3 Physical exam. The middle figure demonstrates cervical animation to identify platysmal bands.

Fig. 20.4 Physical exam. The lower figure demonstrates pinching the soft tissue at rest and with muscle contraction to distinguish the cervical bulk caused by preplatysmal fat from bulk caused by subplastysmal structures. Bulk due to subplastysmal structures “escapes” from the pinch with contraction.

Anatomy

Procedures on the neck are designed to modify the submental/submandibular regions and the cervicomental angle regions by reduction and/or relocation of volume. The excess volume exists in three planes: the superficial plane between the skin and platysma, the intermediate plane comprised of the platysma and interplatysmal fat lying between the bilateral medial platysma edges, and the deep plane beneath the platysma containing the subplatysmal fat, the anterior belly of the digastric muscles, and the submandibular glands.

The platysma muscles are thin bilateral structures that extend from the SMAS in the face to the clavicles. There are three variations of platysmal anatomy in the submental region (Fig. 20.5):

• Type I (75%): Interdigitation of the plastysma muscles to a point 1–2 cm posterior to the mandibular symphysis.

• Type II (15%): Interdigitation of the plastysma muscles from the mandibular symphysis to the thyroid cartilage.

• Type III (10%): No interdigitation.

Fig. 20.5 Three types of platysmal anatomy.

Thus it is apparent that the majority of patients don’t have a significant extent of medial platysmal interdigitation. With age the retaining ligaments that maintain the free medial edges approximated to the deep cervical fascia attenuate. The unrestrained edges shorten and pull away from the underlying structures resulting in the formation of plastysmal bands.

In patients with minimal to no plastysmal interdigitation, interplatysmal fat is found in the submental region between the medial edges of the two platysma muscles. This interplatysmal fat is considered a structure of the intermediate plane, but is contiguous with the subplatysmal fat of the deep plane. In those with complete interdigitation (no platysmal decussation) there is no interplatysmal fat and the fat referred to as “subplatysmal fat” is located deep to the plastysma, superficial to, between, and lateral to the anterior bellies of the digastric muscles.

The anterior bellies of the bilateral digastric muscles may be hypertrophied or more visible in some patients resulting in excess submental bulk. These muscles are paired bilateral structures that extend between the lesser cornu of the hyoid bone and the posterior surface of the mandible on either side of the symphysis (Fig. 20.6). Each anterior belly forms one side of the bilateral submandibular triangles. The other two borders of the submandibular triangles are the posterior belly of the digastric muscle and the inferior edge of the body of the mandible. These triangles contain the submandibular gland, facial artery and vein, lingual nerve and the marginal mandibular branch of the facial nerve. Motor innervation of the anterior belly of the digastric muscle is a branch of the mandibular division of the trigeminal nerve. The muscles function as week depressors of the mandible. Excision proceeds without noticeable alteration in function.

Fig. 20.6 Digastric muscle and submandibular gland anatomy.

The submandibular gland, a salivary gland, may produce a visible bulge in the region of the submandibular triangle, when it is hypertrophied and/or ptotic (Figs 20.7, 20.8). This bulge disrupts the otherwise planar surface that typifies the smooth contour of a youthful appearing neck. The facial artery and vein run obliquely over the posterior portion of the gland and the marginal mandibular can run horizontally across the superior aspect of the gland in a plane just superficial the facial artery and vein. Both the lingual nerve and the hypoglossal nerve lie deep to the gland. These vascular and neural structures are located in an extracapsular location, thus intracapsular resection of the gland is one strategy to reduce the risk of excessive bleeding and nerve injury.

Fig. 20.7 Lateral view of submandibular gland.

Fig. 20.8 Inferior view of submandibular gland – subplatymal fat removed from digastric and mylohyoid muscles.

Technical steps

The majority of deep plane procedures are preceded by lipectomy of the superficial neck plane. Subcutaneous infiltration of a local anesthetic containing epinephrine is performed. After the epinephrine-associated vasoconstriction is evident, an incision 3 to 5 cm in length is made parallel to and just posterior to the submental crease (Fig. 20.9). With the aid of a headlight the submental skin flap is raised leaving at least 5 mm of fat deep to the skin. The extent of the dissection is individualized. In most patients the dissection is carried at least to the thyroid cartilage. The mandibular retaining ligaments are released by carrying the dissection anteriorly and laterally. This facilitates the production of a straight and well-defined mandibular border upon skin redraping. One may also consider delaying the final paring of preplatysmal fat in the submandibular region (inferior to the mandibular body) until after SMAS and platysmal tightening as the location of the desired fat for removal may change with relocation of those deeper structures.

Fig. 20.9 Location of submental incision 2 mm posterior to the submental crease.

Open lipectomy of the superficial plane is performed most effectively when the skin flap is elevated with an even thickness retaining some subcutaneous adipose tissue (5 mm). The fat remaining on the platysma (preplatysmal) and between a decussated platysma (interplatysmal, see Fig. 20.8) is then removed with direct scissors or Bovie dissection, or by suction-assisted lipectomy (SAL). Small (3 mm or less) and single aspiration port cannulas are used, and fat is aspirated from the surface of the platysma, not from the deep surface of the skin.

Access to the subplatysmal (deep) plane is obtained in a medial to lateral approach. In patients with type III platysmal anatomy the medial edges of the platysma are elevated with scissor spreading dissection. In patients with varying degrees of submental platysmal interdigitation (types I and II), a midline incision is made in the platysma with the coagulating current to created two free medial edges. The plastysma is elevated to the level of the thyroid cartilage and laterally far enough to expose the subplatysmal fat, the anterior bellies of the digastric muscles and the submandibular glands (Fig. 20.10). Subplatysmal fat is excised by direct excision or electrocautery. If the anterior bellies of the digastric muscle are to be left unmodified, the interplatysmal and subplatysmal fat is resected only to the caudal surface of the muscles in order to prevent the formation of a submental depression. If a muscle reduction is planed, fat is resected to the projected level of the muscle excision (Fig. 20.11).

Fig. 20.10 Exposure of subplatymal fat, anterior belly or disgastric, and submandibular gland via a submental incision.

Fig. 20.11 Before and after photographs of a patient who has undergone a neck lift with subplatysmal fat reduction

(courtesy of F.N.).

Total or subtotal resection of hypertrophied anterior bellies of the digastric is performed, depending on the preoperative and intraoperative assessment. In a subtotal resection, a hemostat is placed in the non-dominant hand to aid in the determination of the level of the tangential excision (Fig. 20.12). The working end of the hemostat is pierced through the muscle fibers to separate those that are to be removed from those that are to be left in place. Electrocautery is used to transect the muscle fibers just posterior to the mandible and just anterior to the hyoid bone. If a total excision is planned the procedure is similar. The hemostat guides transection of the full thickness of the muscle in the same locations as described for the subtotal excision (Fig. 20.13).

Fig. 20.12 Subtotal resection of the anterior belly of digastric muscle.

Fig. 20.13 Before and after photographs of a patient who has undergone a neck lift with subtotal resection of the anterior belly of digastric muscle (courtesy of F.N.).

Subsequent to the management of hypertrophied digastric muscles, the submandibular glands are reassessed by direct inspection. Subtotal resection is sometimes indicated to prevent a postoperative bulge. A relatively safe approach to resection is intracapsular with piecemeal removal of the parenchyma (Fig. 20.14). The gland is brought into view with a suture or an Allice clamp. An incision is made in the capsule at the caudal pole of the superficial lobe of the gland to avoid the facial vessels and marginal mandibular nerve associated with the cephalic pole. Following entry into to the intracapular space, electrocautery is used to resect the glandular parenchyma in an incremental fashion. The neck is flexed and re-evaluated with the skin redraped periodically to prevent over-resection (Fig. 20.15).

Fig. 20.14 Intracapsular resection of the submandibular gland.

Fig. 20.15 Before and after photographs of a patient who has undergone a neck lift with intracapsular resection of submandibular gland (courtesy of F.N.).

Following the management of the subplatysmal fat, hypertrophied anterior bellies of the digastric muscles, and ptotic and/or hypertrophied submandibular glands, the structures responsible for deep plane bulk, attention must be paid to the repair of the intermediate plane, the platysma, in a fashion that restores support to this structure. The goal of plastysma modification is to lessen an obtuse cervicomental angle. This is accomplished by placing the plastysma under tension with forces applied to it both laterally and medially in vectors perpendicular to the long access of its fibers. Lateral plastysmaplasty can take the form of plication or the elevation as a flap and is addressed in the subsequent paragraph.

Many deep plane neck procedures are performed in conjunction with facial rhytidectomies. In such cases, it is recommended by some, including but not limited to Stuzin, that SMAS flap elevation and fixation or SMAS plication generally should be performed prior to lateral plastysmaplasty and before midline platysmaplasty, in order to elevate and fix the malar fat pad and the jowls cephalically prior to the application of platysmal forces that might otherwise lock these midface structures in a dependent position. However others, including the senior author of this chapter (Nahai) and Feldman do not believe that this is critical.

Lateral plastysmaplasty is performed using flap elevation and fixation or plication (Fig. 20.16). The vector and location of the traction force applied is more important than the method employed to generate the force (Fig. 20.17). The force should be applied to the lateral platysma inferior to the gonial angle and oriented in a vector perpendicular to the midline of the neck. The greatest force is applied in the location where the apex of the cervicomental angle is desired, the level of the hypoid bone. This location and vector results in a more acute cervicomental angle and helps further define the outline of the mandible.

Fig. 20.16 Lateral platysma flap fixation.

Fig. 20.17 Vectors of plastysmal tightening. Arrows demonstrate both vertical and horizontal vectors.

The midline platysmaplasty is performed last. The medial edges of the plastysma muscle are repaired at the midline from the mentum to the inferior edge of the thyroid cartilage. The midline plication is performed with the head positioned so that the cervicofacial angle is 90 degrees or less to reduce tension. Following completion of the midline plication, horizontal myotomy of the medial edges of the platysma is performed for a distance of 3 cm bilaterally at the caudal extent of the plication. The purpose of this muscle transection is two-fold. First, myotomy allows the plastysma composite to shift cephalically under the tension created by the medical repair and lateral repositioning and thus deepens the cervicomental angle. Second, the transection will help reduce the recurrence of platysma bands. The skin is dissected further as is necessary in order to permit sufficient redraping. A closed suction drain is placed and brought out of the surgical plane laterally. The submental incision and postauricular incisions, if present, are closed and a loose, non-binding dressing is applied.

Postoperative care

Patients are generally kept overnight for observation. The following morning the operative dressing and the drain are removed. A compressive, non-binding, garment is worn for 5 days continuously, except when showering, and then the balance of 10 days at night only. Patients should also be instructed to position their heads so that their necks are gently extended. Cervical flexion can increase edema through venous obstruction, place excess tension on mastoid region closures, and diminish adherence of the skin to the underlying structures. The avoidance of placing a pillow solely behind the head will decrease the risk of these untoward occurrences.

Complications

Acute complications include hematomas, seromas, and injury to the marginal mandibular branch of the facial nerve. The rate of hematomas in neck lifts is 3% and in the senior author’s experience is not increased with the addition of deep plane procedures. Expanding hematomas represent a surgical emergency due to the potential for airway compromise and skin flap necrosis. They should be explored and drained urgently. Small non-expanding collections of blood may be aspirated or milked to the drain. Often small hematomas are not recognized for several days when edema starts to ebb. At the 7–14 day time period, the clot lyses and can be aspirated percutaneously.

Seromas also become evident following the resolution of edema. Seromas are aspirated at regular intervals until they have abated entirely. If a fluid collection appears soon after drain removal and the patient reports enlargement with meals in the context of subtotal submandibular gland resection, a sialoma may be present, although this is very rare. In such cases consideration should be given to aseptically replacing a drain and/or the initiation of systemic glycopyrolate administration to reduce saliva production.

Injury to the marginal mandibular branch of the facial nerve results in weakness of depression of the ipsilateral hemi lower lip due to denervation of the depressor anguli oris and mentalis muscles. In most cases the injury is not permanent and function returns in 24 hours to 3 months. If permanent asymmetry with smiling remains, symmetrisizing procedures can be employed.

Chronic complications are generally aesthetic in nature. The most common complication in aesthetic procedures of the neck is surface contour irregularity and an over-reduction of volume in the superficial plane in an effort to reduce neck volume that is actually attributable to the intermediate and/or deep planes. Overzealous or asymmetric subcutaneous fat removal can be ameliorated to some extent by adipose or adipodermal grafts. The contour problems are sometimes compounded by the presence of adhesions between denuded dermis and the platysma muscle, resulting in dynamic puckering with cervical motion and animation. This complication often requires re-elevation and redraping of the skin with the interposition of the adipose containing grafts.

The failure to recognize hypertrophy of the digastric muscle and/or ptosis of the submandibular gland in the preoperative assessment will result in inadequate reduction of deep plane volume. The converse complication occurs when overcorrection of volume is performed, resulting in submental depression that is accentuated if one fails to plicate the platysma at midline.