History

Surgery on the lower-third of the face may be performed to reconstruct congenital or acquired deficits or to enhance facial aesthetics. These goals can be accomplished by any combination of bony osteotomies or ostectomies, alloplastic augmentation, skin resurfacing or redraping, and/or soft tissue fill. While soft tissue operations of the face are described elsewhere in this text and orthognathic movements of the midface and mandible are beyond the scope of this chapter, we will highlight autologous genioplasty. Obwegeser provided the first detailed description of bony chin surgery in 1957. The osseous genioplasty, however, was not popularized until 1964 when Converse reported the horizontal osteotomy of the mandible to reposition the genial segment. Since then, chin surgery has become a common aesthetic procedure that can complement other procedures such as rhinoplasty, rhytidectomy, or platysmaplasty.

Although improvements in alloplastic materials developed in the 1970s and 1980s have led many surgeons to choose alloplastic chin augmentation, the osseous genioplasty should not be overlooked. The osseous genioplasty remains a versatile operation that can address a wide variety of chin deformities ranging from microgenia to macrogenia to chin asymmetry. Moreover, osseous genioplasty avoids alloplastic materials and the attendant complications that can occur with a long-term foreign body in situ. This chapter will detail the technical aspects of osseous genioplasty.

Physical evaluation

While the neoclassical artistic paradigm recommends that the lower-third of the face be divided into equal thirds – the upper lip, the lower lip, and the chin – such rules are only of limited utility in surgical planning. One of the principal errors a surgeon can make in assessing the lower-third of the face is to limit evaluation to the chin only – particularly the bony component of the chin. Rather, not only must the aesthetics of the chin be balanced in relation to the facial structure, but it is necessary to take into consideration the stature and sex of the patient as well. When evaluating the chin, a systematic approach to the physical examination is helpful. For example, when honing in on the lower third of the face, a step-by-step evaluation from nose to chin should include the lower midface, nasolabial folds, upper and lower lip relationship, incisor tooth show, labiomandibular fold, lower lip eversion and inclination, height and depth of the labiomental fold, chin pad thickness, static soft tissue ptosis, and dynamic chin pad motion with smile.

Large-format frontal, oblique, basilar, and lateral photographs in repose and animation are essential. Posteroanterior and lateral cephalograms, as well as a panoramic X-ray, can also be helpful. Any evaluation of the lower third of the face should also include the following points:

1. Midface evaluation

Malar fat pad

In a youthful midface, the superior border of the triangular shaped malar fat pad lies along the orbital rim and extends laterally to the zygomas (Fig. 35.1). The lateral border can be identified by drawing a line from the lateral canthus to the lateral commissure. The malar fat pad is located beneath the skin and subcutaneous fat, but it is superficial to the superficial muscular aponeurotic system (SMAS). It is fibrous and fatty, and it is readily distinguishable from the overlying subcutaneous fat. With advancing age, the malar fat pad descends inferiorly and medially. Ptosis of the malar fat pad empties the midface and accentuates tear-trough and nasolabial folds. To a lesser extent, this displacement also results in the formation of labiomandibular folds (marionette lines) and jowls.

Fig. 35.1 In a youthful midface, the superior border of the triangular shaped malar fat pad lies along the orbital rim and extends laterally to the zygomas. With advancing age, the malar fat pad descends inferiorly and medially. Ptosis of the malar fat pad empties the midface and accentuates the tear-trough, nasolabial folds, labiomandibular folds (marionette lines), and jowls.

Nasolabial fold

The cutaneous insertion of the zygomaticus major/minor and levator labii superioris muscles determines the nasolabial fold. In a sense, the nasolabial fold may be considered a fasciocutaneous ligament necessary for lip elevating muscles to initiate a smile. Laxity of this fasciocutaneous ligament causes the malar fat pad to travel inferomedially over the crease to deepen the nasolabial fold.

Labiomandibular fold

The depressor anguli oris superiorly and the mandibular ligaments inferiorly determine the labiomandibular fold (marionette line), which is converted into a fold as a result of the laxity of the masseteric ligaments that occurs with age.

2. Lip evaluation

Proportion of lips

On profile, the upper lip ideally projects approximately 2 mm beyond the lower lip, which, in turn, ideally projects 2 mm beyond the most anterior aspect of the chin (the soft-tissue pogonion). The lower lip is normally fuller than the upper lip. The fullness of the lower lip determines the inclination of the lower lip, which affects the appearance of the chin.

Labiomental fold

The position of the labiomental fold contributes to the appearance of the vertical height of the chin. A high labiomental fold will make the chin appear larger, and a low labiomental fold will make the chin appear smaller and more defined. A shallow or indistinct labiomental fold makes the chin appear larger because the demarcation between the lower lip and the chin pad is less well defined. The surgeon can also imagine the labiomental fold in profile as an angle (Fig. 35.2). A shallow fold has an obtuse angle and a deep fold has a more acute angle. Viewing the labiomental fold as an angle can be helpful when planning chin surgery. For example, performing an augmentation genioplasty on a patient with a low, deep labiomental fold will make the fold angle more acute and the fold will appear too deep.

Fig. 35.2 A&B, The surgeon can imagine the labiomental fold in profile as an angle. A shallow fold has an obtuse angle and a deep fold has a more acute angle. Viewing the labiomental fold as an angle can be helpful when planning chin surgery.

Inclination of the lower lip

In conjunction with the labiomental fold, the inclination of the lower lip also affects one’s perception of chin size. The lower lip inclination helps to create a demarcation between the lip and the chin pad. Therefore, the more vertical the lower lip, the larger the chin appears.

4. Chin evaluation

Chin pad thickness

The chin pad is assessed by palpation. Chin pad soft tissue projection should be maximally at the level of the pogonion (Fig. 35.3). Static chin pad position should be noted. A chin pad cleft represents a cleft in the mentalis muscle as well as a deficiency of the chin pad soft tissue.

Fig. 35.3 Drawing of idealized chin proportions. Chin pad soft tissue projection should be maximally at the level of the pogonion.

Bony component

It is important to assess the size of the bony chin, especially in the case of the large chin. This is accomplished through palpation and dynamic evaluation: when smiling, a large chin due to a large bony component becomes even more pronounced, whereas a large chin due to excess soft tissue will appears better as the soft-tissue becomes effaced. Cephalograms are especially useful in determining the size and shape of the bony component.

Orientation of deficiency or excess

The vertical, anteroposterior, and transverse dimensions of the dysmorphic chin should be analyzed.

Vertical 

The vertical height of the chin extends from the menton to the nadir of the labiomental fold. The appearance of the chin is affected not only by the size of the bony chin, but also by the pad percentage and the height and distinctness of the labiomental fold.

Anterior 

Normally, maximal chin projection is at the level of the pogonion. In some patients, there is a prominent symphyseal ridge or bulky mentalis muscle which causes increased chin projection just below the labiomental fold. In some cases, bony reduction is indicated.

Transverse 

Chin point projection should coincide with the facial midline. Transverse chin point asymmetry should be noted.

Shape

The shape of the chin is important in preoperative planning. Women usually prefer a smaller, rounder chin while men tolerate a larger, more angular chin.

Anatomy

In its vertical dimension, the lower third of the face extends from the base of the columella to the most inferior aspect of the chin. Anteroposteriorly, it extends from the gnathion to the submental crease and transversely to the angles (gonion) of the mandible.

The anterior nasal spine is in the midline of the maxilla. Laterally, the concave nasal notches form the sills of the piriform aperture. The maxillary alveolar process contains the vertical wavelike eminences of the maxillary dentition; the canine root is most prominent and extends nearly 28 mm from the incisal edge. A patient with perinasal midfacial flatness may have an underlying maxillary skeletal deficiency. Ptosis of the soft tissue and malar fat pads tends to accompany this type of bony deficiency causing deep nasolabial folds. The cutaneous insertion of the zygomaticus major/minor and levator labii superioris muscles determines the nasolabial fold. Laxity of this fasciocutaneous ligament contributes to malar fat pad descent inferomedially over the crease, causing deepening of the nasolabial fold. The vermillion of the upper lip begins at the white roll. The upper lip vermillion is divided into three distinct parts: the central tubercle and lateral limbs. The upper lip ideally projects about 2 mm beyond the lower lip, but it is less full than the lower lip.

The lower lip rolls outward creating an infralabial line of inclination (seen on profile) connecting the white roll to the labiomental fold. The labiomental fold is the point of greatest concavity and defines the superior extent of the chin pad. The mandibular symphyseal spine originates in the midline of the mandible beneath the labiomental fold. The symphyseal spine divides to enclose the mental protuberance. On either side of the symphysis, just below the mandibular incisors, are the incisive fossae. The incisive fossae provide origin for the mentalis muscle (Fig. 35.4). The mentalis muscles – so-named because of its association with the expressions of pondering and doubt – insert superiorly into the dermis to elevate and protrude the lower lip. The mentalis muscle can be divided into horizontal and oblique fibers. The division between these fibers defines the labiomental fold (Fig. 35.4). The labiomandibular crease is determined by the depressor anguli oris superiorly and the mandibular ligaments inferiorly, which then converts into a fold as a result of senile laxity of the masseteric ligaments. The mandibular retaining ligaments arise from the parasymphysial mandibular body and insert into the skin inferior to the insertion of the depressor anguli oris. The mandibular ligaments define the anterior extent of the jowls.

Fig. 35.4 Sagittal view of the chin anatomic dissection. The incisive fossae provide origin for the mentalis muscles. The mentalis muscle can be divided into horizontal and oblique fibers. The division between these fibers defines the labiomental fold.

All muscles of the lower third of the face are innervated by branches of the facial nerve except the anterior bellies of the digastrics and the mylohyoids, which are innervated by the third division of the trigeminal nerve. The second division of the trigeminal nerve provides sensory innervation to the midface. The inferior alveolar nerve provides sensory innervation to the chin; unfortunately, its intraosseous anatomic course makes it particularly susceptible to injury during osseous genioplasty. The inferior alveolar nerve enters the mandibular foramen on the medial aspect of each mandibular ramus and usually travels through a single mandibular canal. The mandibular canal terminates by descending 4.5 mm inferior to the mental foramen, looping 5.0 mm mesially, and then turning distal to deliver three branches of the mental nerve. The mental foramina may be reliable located beneath the second premolars. The mental nerve branches supply sensory innervation to the mandibular teeth, mucosa, lower lip, and chin.

Technical steps

While soft tissue surgery or alloplastic operations in the lower third of the face can be performed under local anesthesia or intravenous sedation, we prefer general anesthesia for nearly all skeletal operations. Patients are positioned supine on the operating table with a pillow under the shoulders to allow the head to extend into a gel head rest. Nasal intubation is unnecessary. Preoperative antibiotics are administered. The mucosa and subcutaneous tissues of the chin are injected with 1% lidocaine with 1 : 100,000 epinephrine.

The chin can be approached intraorally or through a submental incision. Either route provides satisfactory exposure to the bony chin. The submental incision does provide an additional opportunity to excise submental skin and subcutaneous tissues if redraping of ptotic tissues is necessary. While the submental scar is usually well tolerated, we choose an intraoral approach whenever possible.

A 3 cm long intraoral incision is made 1 cm cephalad to the labiobuccal sulcus and electrocautery dissection is carried down through the subcutaneous tissues. The mentalis is divided and the periosteum is scored. Subperiosteal dissection is performed to expose the chin from mental nerve to mental nerve. The midline of the mandible is marked with a sagittal saw and the inclination of the osteotomy is decided. If the surgeon plans to perform a sliding genioplasty, the angle of the osteotomy will affect the vertical height of the chin as the genial segment is advanced sagittally. For example, an acute osteotomy slope angle (<70° relative to perpendicular line dropped from occlusal plane) will lead to a more vertical reduction for any given sagittal advancement. In contrast, an obtuse slope angle (>90°) will lead to a vertical elongation of the chin (Fig. 35.5). While a surgeon may choose a sliding genioplasty to advance and vertically reduce the chin, the change in sagittal advancement and vertical reduction is a fixed ratio based on the slope of the osteotomy. After the osteotomy angle is determined, the osteotomy is performed at least 6 mm below the mental foramina in order to avoid the intraosseous course of the inferior alveolar nerves.

Fig. 35.5 Drawing of sliding genioplasty (left side) and jumping genioplasty (right side). A, The osteotomy angle is selected and the osteotomy is performed at least 6 mm below the mental formina in order to avoid the inferior alveolar nerves. B, The genial segment is advanced and fixed with a lag screw technique. C, The advanced genial segment is contoured with a burr as necessary to adjust sagittal projection and labiomental fold depth and angle. D, The advanced genial segment is contoured with a burr as necessary to adjust sagittal projection and labiomental fold depth and angle. E, Final contour adjustments are made on the sliding genioplasty. F, The genial segment is jumped on to the anterior surface of the mandible and fixed with a lag screw technique. The segment is then contoured with a burr as necessary to adjust sagittal projection and labiomental fold depth and angle. G, Final contour adjustments are made on the jumping genioplasty.

Once liberated, the bony segment is advanced anteriorly until the desired increase in sagittal projection is achieved. The attachments of the genioglossus, geniohyoid, anterior digastrics, and mylohyoid muscles to the posterior (labial) surface of the genial fragment are maintained to preserve the blood supply. An advancement of 5–7 mm is typical, but advancements of 10 mm are possible. If the surgeon is advancing the chin more than 10 mm, he should reconsider the maxillomandibular relationship as an orthognathic movement may be indicated.

Vertical elongation of the chin is usually achieved by interposition grafting (typically hydroxyapatite or bone graft) within the intercalary gap rather than choosing an obtuse osteotomy angle (Fig. 35.6). Conversely, if a reduction in the vertical height of the chin is necessary, a wafer of bone can be removed (Fig. 35.7). Chin asymmetry can be corrected shifting the osteotomized fragment laterally.

Fig. 35.6 Vertical lengthening of the chin with bone graft or hydroxyl apatite. A, The osteotomy is performed at least 6 mm below the mental foramina. B, The genial segment is liberated and a bone graft or hydroxyl apatite bone substitute is inserted into the intercalary gap. C, The vertical lengthened genial segment fixed with a lag screw technique.

Fig. 35.7 Vertical reduction of the chin by removing a wafer of bone. A, Two parallel osteotomies are performed at least 6 mm below the mental foramina. B, The wafer of bone is removed. C, The vertical shortened genial segment fixed with a lag screw technique.

The genial segment can also be transposed or jumped to the anterior surface of the mandible. When performing a jumping genioplasty, a side cutting burr can be used to contour the posterior surface of the osteotomized segment in order to allow it to fit appropriately to the anterior surface of the mandible (Fig. 35.5). Contouring the posterior surface of the genial segment also enables the surgeon to control the amount of sagittal advancement.

Once in proper position, the osteotomized fragment is rigidly secured to the mandible using a lag technique with two or more countersunk screws (Fig. 35.5). It is important to note that the blood supply to the genial segment is provided through the genioglossus, geniohyoid, digastric, and mylohyoid muscles which originate along the mental spine, mental spine, digastric fossa, and mylohyoid line, respectively. The surgeon must preserve the muscular blood supply in order to avoid avascular necrosis of the genial segment.

Finally, the anterior surface of the secured genial segment is contoured using the side cutting burr to fine tune the desired pogonial sagittal projection and labiomental angle. When estimating the amount of desired sagittal advancement at the pogonion, we assume a 1 : 1 relationship between bony advancement and soft tissue change. A small drain can be passed transcutaneously through the submental skin. The gingivobuccal incision is closed with interrupted chromic sutures. Typical results are shown in Figs 35.8–35.10.

Fig. 35.8 21 year-old female presents with long non-projecting chin. The patient underwent an oblique osteotomy (~51° angle) of the chin (4 mm vertical reduction and 5 mm sagittal advancement) and a LeFort I (4 mm vertical reduction and 5 mm sagittal advancement) A. Preoperative frontal view. B. Postoperative frontal view at 6 months. C. Preoperative lateral view. D. Postoperative lateral view at 6 months.

Fig. 35.9 25 year-old male presents with sagittally deficient chin, class III malocclusion, and lip incompetence. The patient underwent a horizontal osteotomy (~ 80° angle) of the chin (0 mm vertical change and 6 mm sagittal advancement) and LeFort I osteotomy (0 mm vertical change and 7 mm sagittal advancement). A. Preoperative frontal view. B. Postoperative frontal view at 1 year. C. Preoperative lateral view. D. Postoperative lateral view at 1 year.

Fig. 35.10 24 year-old male presents with sagittally deficient and vertically long chin, class III malocclusion, and lip incompetence. The patient underwent an oblique osteotomy (~ 70° angle) of the chin (2 mm vertical change and 5 mm sagittal advancement), LeFort I osteotomy (3.5 mm vertical reduction and 8 mm sagittal advancement), and a bilateral sagittal split osteotomy of the mandible with counter-clockwise rotation. A. Preoperative frontal view. B. Postoperative frontal view at 18 months. C. Preoperative lateral view. D. Postoperative lateral view at 18 months.

Treatment of a large chin can also be performed through a similar approach. Reduction macrogenia can be performed with a side-cutting burr; however, we must caution the reader that burring can produce an unnatural, flattened appearance to the chin and soft tissue ptosis giving a double chin. Instead, we prefer to reduce a large chin using the osseous genioplasty approach described above except we make an effort to limit the subperiosteal dissection as much as possible so that as the osteotomized segment is set back, the overlying soft tissues are drawn with the segment. Since bony set-back or reduction moves the soft-tissue pogonion posteriorly, care must be taken not to overcorrect patients with a preoperative obtuse labiomental fold. Conversely, there is more leeway for bony reduction if the labiomental fold was deep preoperatively. After fixation of the genial fragment with wires, the segments lateral wings are smoothed by burring.

Postoperative care

A light compressive dressing of stretch tape (e.g. Elastoplast® tape) is applied to the chin across the labiomental fold and beneath the chin to ensure soft tissue contact with the underlying bone. The dressing is worn continuously for 4 days and then removed. Drains, if employed, are removed within 24 hours.

Complications

Surgical treatment of the lower third of the face can result in any complication common to surgical procedures, including infection, scarring, hematoma, nerve injury, etc. Equally noteworthy, aesthetic sequelae from faulty preoperative planning or technical execution are difficult to conceal. Fortunately, when the surgeon has appropriately analyzed the chin problem and reviewed the anatomy, osseous genioplasty can be performed on an outpatient basis with few complications.

In order to reduce complications after osseous genioplasty, we highlight the following points: (1) The mental nerve can be injured during the incision, subperiosteal dissection, retraction, osteotomy and/or screw fixation. Remembering that the mental foramina are usually located beneath the second bicuspids serves as an important guide when making the incision and performing subperiosteal dissection. We commonly switch from a square-ended (sharp) elevator to a round-ended (blunt) elevator when nearing the mental foramina in order to avoid injuring the mental nerves. Overzealous retraction can also cause neuropraxia or even axonotmesis. When designing the osteotomy, it is important to remember that the inferior alveolar nerve travels as much as 4.5 mm inferior and 5 mm mesial to the mental foramina. We commonly leave a 6 mm margin beneath the mental foramina and the osteotomy. (2) The mandibular tooth roots can be injured during the osteotomy or screw placement. It is important to remember that the canine tooth root may extend as much as 28 mm from the incisal edge. While the consequences of screw injury to the tooth root may be debated, it is best to avoid injury by simply placing screws mesial or distal to the canine. (3) Hematomas can result in ectopic bone formation and subsequent contour irregularities. It is best to avoid hematomas with a drain and compressive dressings. (4) Inadequate genial fixation will result in either relapse or asymmetries. We avoid this complication by ensuring satisfactory lag screw fixation on the table rather than relying on postoperative dressings and neo-osteogenesis to stabilize the fragment.