Introduction

The chin is the lower topographic limit of the face and thus plays an important role in the perception of appropriate facial proportions.^4,5 A vertically deficient or excessive chin places the lower third of the face out of balance relative to the middle and superior thirds of the face.⁶ Horizontal deficiency or excess diminishes facial pulchritude, most notably in profile (Figs 13.1 & 13.2). Additionally, the chin has a pivotal role as a reference in the appreciation of other facial features, most notably the nose. A large nose is often paired with a deficient chin and they have a reciprocally negative effect on the appearance of each other and on overall facial attractiveness (Fig. 13.3).^7–9

Fig. 13.1 Horizontal microgenia.

Fig. 13.2 Horizontal macrogenia.

Fig. 13.3 The synergistic facial disharmony of a large nose paired with microgenia.

Improvements in the chin can be achieved by osteotomy or by the use of implants or grafts for augmentation.¹⁰ Osseous procedures include burr reduction (ostectomy), osteotomy with caudal segment repositioning, osteotomy with grafting or osteotomy with segmental sectioning.^11–15 Augmentation genioplasty can be accomplished with autologous tissue grafts such as bone or cartilage or, more commonly, with alloplastic implants.^16,17 The benefits of alloplastic augmentation include a shorter and less technically demanding procedure. However, alloplastic genioplasty can pose limitations in achieving large augmentation without causing lip retraction, has a lower success rate for correction of asymmetry and offers very limited potential to change the vertical dimension of the chin.¹⁸

Anatomy

From external to internal, the layers of the chin include skin, subcutaneous fat, muscles, periosteum and bone. The depressor angularis, depressor labi inferioris and mentalis attach to the anterior plane of the chin. The geniohyoid, genioglossus, mylohyoid and anterior belly of the digastric attach to the lingual aspect. Following elevation of the anterior periosteum and horizontal osteotomy, the blood supply of the caudal chin segment is maintained via terminal lingual artery periosteal perforating branches that travel through the musculature attached to the lingual side (Figs 13.4 & 13.5).

Fig. 13.4 Muscles that attach to the lingual aspect of the chin.

Fig. 13.5 Demonstration of lingual aspect musculature left intact following osteotomy to preserve blood supply to the caudal segment.

The mental nerve supplies sensation to the anterior mandibular gingiva, mucosa and lower lip. It is a continuation of the inferior alveolar nerve and exits the mandible via the mental foramen. The mental foramen is located in the vertical plane between the first and second mandibular premolars. In the terminal portion of its course, as it travels posterior to anterior, the nerve ascends to the foramen (Fig. 13.6). This upward trajectory must be understood when planning the location and angle of a horizontal osteotomy.^19–21 In order to avoid direct nerve injury, the osteotomy should be placed at least 5 mm caudal to the foramen and be executed at a caudal-oblique angle.

Fig. 13.6 Sensory nerves. The inferior alveolar nerve transitions to the mental nerve as it exits the mental foramen. Prior to this transition the nerve makes a brief pass caudally then cephalically to the foramen. Horizontal osteotomies are made at least 5 mm caudal to the mental foramen to reduce the risk of direct neural injury.

Indications and Contraindications

The presence of some medical conditions influences the type of genioplasty that is prudent. Generally, patients with diabetes mellitus or immune deficiency are not ideal candidates for alloplastic augmentation.^1,22 Patients over the age of 60 years old with a mild-to-moderate horizontal microgenia are better candidates for alloplastic augmentation. On most other patients osteotomy is preferred, although the use of implants is not considered inappropriate. Patients who smoke cigarettes are not the ideal candidates for the use of grafts as a chin augmentation material.

Preoperative History and Considerations

The cardinal determinants of chin harmony are its projection symmetry and vertical length. Assessment of the vertical dimension of the chin is performed first in frontal view analysis. The face is divided into two anatomic portions using imaginary lines placed at the eyebrow level and subnasale. The three segments that these lines create should be equal in the harmonious face (Figs 13.7 & 13.8).

Figs 13.7 and 13.8 The face is divided into three equal sections by placing imaginary lines at the glabella and subnasale. Assessment of these divisions aids in the analysis of facial vertical proportions.

To assess the vertical dimension of the chin, the lower third is further subdivided using a line passing through the stomion. The distance from the stomion to the menton should be twice the length of the distance between the subnasale to the stomion. Additionally, the distance from the stomion to menton should be equal to the distance from the stomion to the line connecting the medial canthi. Deviation from equality in either of these comparisons is measured in millimeters and included in the plan for vertical modification of the chin.

The terminus of the female chin is a single light reflfection. In the male chin, there are dual light reflections indicating the underlying increased width and rectangular shape of the chin. To determine the chin symmetry, a vertical line is drawn passing through the midglabella, the tip of the nose (as long as the nose is straight) and the philtral dimple. The midpoint of a symmetrically located chin will fall on this line (Fig. 13.9).⁸ If chin asymmetry is identified, its cause should be elucidated as it impacts procedure choice. To decide whether the chin asymmetry is related to maxillary/mandibular disharmony or is intrinsic to the chin itself, the horizontal planes of the mouth and the eyes are examined. The intercommissural line should be parallel to the intercanthal line. Otherwise, vertical asymmetries of one or both of the jaws are likely to be present and genioplasty alone may not correct this condition fully. If the intercommissural line parallels the intercanthal line, a pure genial asymmetry is present and a genioplasty with osteotomy can be planned to correct the deformity (Figs 13.10 & 13.11).

Fig. 13.9 Horizontal symmetry can be assessed by the placement of vertical dividing line. This line connects the midglabella, tip of the straight nose and philtral dimple. The topographic center of a symmetric chin will also lie on this line.

Figs 13.10 and 13.11 The lower facial third is further subdivided into an upper one-third and lower two-thirds by placing a line at the stomion. The stomion to menton length is twice as long as the subnasale to stomion length when appropriate vertical chin height exists.

Horizontal excess or deficiency is detected better in profile. There are multiple methods to determine ideal chin projection. The use of Riedel’s plane is simple and practical. With the ideal chin projection present, the most projecting portion of the upper lip, lower lip and chin are all tangent to the same line (Fig. 13.12). If the chin lies posterior to the Riedel’s plane, horizontal microgenia exists. If the chin lies anterior the plane, horizontal macrogenia exists.

Fig. 13.12 Reidel’s line. The most projecting portions of the upper lip, lower lip and chin are all tangent to this line when lower facial harmony is present.

The labiomental groove should be 4 mm deep in a woman and 6 mm in a man. A deficient chin with a deep labiomental groove should not be treated with augmentation alone in most incidences. These patients are better candidates for orthognathic surgery rather than genioplasty. Although independent of the associated pathology, a deep labiomental groove can also be treated by adding autologous fat, cartilage or bone grafts.

An intraoral examination is mandatory in the assessment of the potential genioplasty patient. The maxillary/mandibular occlusal relationship is carefully examined. Significant periodontal disease should be identified and adequately treated prior to genioplasty to decrease the risk of infectious complications.

Life-size photography with soft tissue cephalometric analysis provides an opportunity for precise preoperative planning of augmentation or osseous genioplasty to the millimeter in both the vertical and horizontal planes.²³ A circumspect facial analysis, coupled with life-size photography, can lead to an accurate definition of chin dysmorphology.

Classification of Chin Deformity

Chin pathology is classified as types I-VII according to the prevailing boney or soft tissue abnormalities.²⁴ The type of deformity dictates which procedure should be utilized in order to attain a pleasing outcome (Table 13.1).

Table 13.1 Classification of chin deformities

Group I deformities encompass macrogenic chins. Moderateto-severe pure horizontal macrogenia is managed by setting back the caudal segment (Fig. 13.13). Correction of pure vertical chin excess requires resection of a horizontal block or wedge segment (Fig. 13.14).

Fig. 13.13 Horizontal macrogenia. In the upper diagram the broken line represents the normal bone outline. The middle diagram demonstrates reduction ostectomy with burr. The lower diagram demonstrates two oblique ostiotomies with resection of the intervening segment and set back to the caudal segment. The shaded area represents contouring of steps-offs following set back with burr.

Fig. 13.14 Vertical macrogenia. The broken line demonstrates an almost horizontally oriented normal chin bone; the excess is almost purely vertical. The middle diagram demonstrates two ostetomies to shorten facial height. In the lower diagram the caudal segment is repositioned cephalically and fixed in place.

Removal of a horizontal segment with setback of the remaining caudal segment is required for combined horizontal and vertical macrogenia (Fig. 13.15).

Fig. 13.15 Combined horizontal and vertical macrogenia. In the upper diagram the broken line demonstrates macrogenia in both the horizontal and vertical plane. The middle diagram demonstrates two obliquely oriented osteotomies to reduce the chin’s horizontal and vertical dimensions. The lower diagram demonstrates the caudal segment positioned posteriorly and cephalically and fixed following removal of the intervening segment.

Group II deformities are comprised of microgenic chins. Augmentation genioplasty for mild or even moderate pure horizontal deficiency is discussed in a later section. A horizontal osteotomy with advancement of the caudal segment is a predictable method of treating horizontal chin deficiency (Fig. 13.16). Pure vertical chin deficiency is addressed with a horizontal osteotomy and caudal repositioning (Fig. 13.17). Combined vertical and horizontal microgenia is managed with repositioning the osteotomized chin segment caudally and anteriorly (Fig. 13.18). With any of these osteotomies, whenever caudal repositioning is performed and a gap greater than 5 mm results, interposition bone grafting or placement of a hydroxyapatite block is indicated. Smaller defects are within the osteoblastic filling (jumping) distance.

Fig. 13.16 Horizontal microgenia. The broken line in the upper diagram demonstrates the normal chin bone outline. In the middle diagram illustrates an oblique osteotomy. In the lower diagram the caudal segment is advanced and fixed in place.

Fig. 13.17 Vertical microgenia. In the upper diagram the broken line demonstrates the normal chin bone outline. The middle diagram an oblique horizontal osteotomy is shown. The lower diagram demonstrates the inferior positioning of the caudal segment. Bone graft or hydroxyapatite is used to fi ll gaps greater than 5 mm.

Fig. 13.18 Combined vertical and horizontal microgenia. In the upper diagram the broken line demonstrates the normal chin bone outline. The middle diagram demonstrates an oblique horizontal osteotomy. In the lower diagram the caudal segment is moved anteriorly and caudally. Bone graft or hydroxyapatite is placed in the gap.

Patients with Group III chin deformities have osseous excess in one direction and deficiency in another. Combined horizontal excess with vertical deficiency is remedied with a horizontal osteotomy followed by caudal and posterior repositioning of the caudal segment (Fig. 13.19). When vertical excess is paired with horizontal deficiency, two osteotomies are performed to remove an anteriorly based wedge of bone. The caudal segment is then advanced cephalically and anteriorly and the gap is closed (Fig. 13.20).

Fig. 13.19 Combined horizontal macrogenia and vertical microgenia. In the upper diagram the broken line outlines the normal chin bone profile. An oblique horizontal osteotomy is shown in the middle diagram. In the lower diagram the caudal segment is moved caudally and inferiorly. Bone graft is used depending on the size of the gap.

Fig. 13.20 Combined vertical macrogenia and horizontal microgenia. In the upper diagram the broken line illustrates normal chin bone outline. Two osteotomies with a wedge ostectomy are demonstrated in the middle diagram. The lower diagram demonstrates cephalic and anterior positioning of the caudal chin segement with fixation.

Asymmetric chins are classified as Group IV. Patients with asymmetric chins are not ideal candidates for genioplasty with alloplasts. Asymmetric chins with normal lower facial height are treated by removing a wedge from the excessive side followed by autografting of that wedge on the side of deficiency (Fig. 13.21). If lower facial height is excessive, the caudal segment is repositioned cephalically and the wedge is discarded. If the face is vertically short only one osteotomy is performed and the caudal segment is differentially moved caudally and the resultant gap is grafted with a segment of bone.²⁵

Fig. 13.21 Chin asymmetry. A, Chin asymmetry with normal anterior lower facial height. A segment is removed and reversed to obtain symmetry. B, An asymmetric chin with deficient overall anterior facial height. A horizontal osteotomy is made and differentially repositioned in a caudal direction. The resulting gap is grafted. C, Asymmetric chin with excess lower facial height. Two osteotomies are performed resulting in a wedge. The wedge is removed and the caudal segment is differentially positioned and fixed in a caudal direction to close the gap.

In the correction of deformities classified as I-IV, the magnitude of caudal bone segment repositioning is determined using the knowledge of the soft tissues responses to the skeletal alterations as outlined (Table 13.2).^8,26

Table 13.2 Soft tissue responses to augmentation or osseous adjustment

Group V patients have pseudomacrogenia, an excess of chin soft tissue that results in the appearance of chin excess. This diagnosis is facilitated by review of radiographic studies demonstrating excess chin soft tissue. This type of chin dysmorphology is corrected through a submental incision. Pseudomicrogenia resulting from vertical maxillary excess and clockwise rotation of the mandible constitutes the group VI chin deformity. This type of deformity requires orthognathic surgery. The group VII chin is the ‘witch’s chin’ characterized by soft tissue ptosis, which is corrected by removal of excessive soft tissues through an elliptical incision in the submental area.

Operative Approach

Osseous genioplasty

Osseous genioplasty refers to alteration of the chin with modifications of the chin bone using two different methods that include ostectomy and osteotomy with caudal segment repositioning. Ostectomy is used exclusively for reduction genioplasty. This is indicated in patients with a chin that is excessive in the horizontal dimension, is long in the central portion only, or appears asymmetric due to excess bone on one side.

Reduction genioplasty by ostectomy is performed under local anesthesia and monitored sedation, or under general anesthesia. This procedure is indicated for mild horizontal or mild vertical macrogenia. The chin is infiltrated with xylocaine containing 1 : 100 000 epinephrine. Access is obtained through a 4 cm submental or an intraoral incision placed on the labial mucosal surface anterior to the sulcus. A 1 cm cuff of mucosa and mentalis muscle must be maintained on the gingival side of the incision to facilitate the repair. The periosteum is elevated off of the anterior surface of the mandibular symphysis. The mental foramina are visualized and the nerves are gently protected with malleable retractors.

An oval burr is used to incrementally remove bone from the anterior surface of the mandible on one half at a time (Figs 13.13 & 13.22). While the burr is being used, the first-generation bone is copiously irrigated with saline containing antibiotics (1 g of cephalosporins in 1 l saline) to avoid thermal damage. More bone is removed centrally and the ostectomy is tapered laterally and superiorly to the level of the mental foramen to prevent irregularities. A caliper is used to assess the amount of bone removed on the first half to have a precise account of how much bone is removed. If the bone is removed on both sides in continuum, it will be difficult to gauge the amount of removed bone precisely. After a sufficient amount of bone is removed on one side, the procedure is repeated on the opposite side.

Fig. 13.22 Burr reduction genioplasty.

Following visual and digital confirmation of smooth contours, the wound is irrigated with antibiotic containing solution. It is important to close the wound in such a way that the mentalis muscle is repaired at the level it was divided and the mucosa is well approximated using 4-0 chromic sutures. A compressive tape dressing or chin sling is placed.

Osteotomy with caudal segment repositioning

While under general or monitored anesthesia care, local blocks with 1% xylocaine containing 1 : 100 000 epinephrine are employed at the mental foramen and soft tissues over the lingual and labial surface of the mandibular symphysis are injected generously to decrease bleeding and postoperative pain (Figs 13.23 & 13.24). Exposure is achieved using the previously described intraoral approach (Figs 13.25–13.28). The inferior soft tissues are left intact to provide the blood supply to the caudal chin segment. Prior to performing an osteotomy, the midline is marked by etching a vertical line in the anterior cortical surface with a saw (Fig. 13.29).

Fig. 13.23 Local injection of anesthesia and vasoconstricting agent in labial mucosa.

Fig. 13.24 Administration of local anesthesia to soft tissues posterior to mandibular symphysis.

Fig. 13.25 The intraoral incision is marked 1 cm from the sulcus on the labial mucosa.

Fig. 13.26 A scalpel is used to make the initial incision.

Fig. 13.27 Electrocautery is used to incise through the remaining soft tissues (mentalis muscle and periosteum) to reach the surface of the osseous chin. A cuff of mentalis muscle and mucosa is left on the cephalic aspect of the mandiblular symphysis to be used later for closure.

Fig. 13.28 A periosteal elevator is used to dissect in a subperiosteal plane taking care not to injure the mental nerves.

Fig. 13.29 A retractor is placed to retract the soft tissues and to protect the mental nerve. A vertical notch is placed to mark the midline of the symphysis to facilitate subsequent identification of midline and attainment of desired caudal segment alignment.

Osteotomies are performed with minimal risk of injury to the teeth and the inferior alveolar nerve. The average length of the lower canine, the longest mandibular tooth, is 25.5 mm. The osteotomy should be performed 5 mm caudal to the projected canine roots, this equates to at least 30.5 mm inferior to the incisal edge. Furthermore, to avoid nerve injury the location of the osteotomy should also be 5 mm caudal to the mental foramen.

A wide saw blade isused to initiate the osteotomy in the central portion of the chin (Fig. 13.30). The saw blade is changed to a narrower one to complete the osteotomies laterally (Fig. 13.31). The osteotomy site is continuously irrigated during the course of the osteotomy. Malleable retractors protect the nerves and the other soft tissues throughout the osteotomy. After the caudal segment is freed it is advanced or retracted to the desired position (Fig. 13.32). A prefabricated step plate is contoured and placed in position to fit the anterior symphysial surface on both sides of the osteotomy (Fig. 13.33). Four screws, two on each side of the osteotomy, are placed (Fig. 13.34). Two osteotomies with removal of an intervening segment are used when a reduction in height is desired (Fig. 13.35). If setback is performed two screws should be sufficient for fixation after which a burr is used to the contour the lateral chin-mandible junctions bilaterally. The wound is then repaired as previously described (Fig. 13.36).

Fig. 13.30 A reciprocating saw with a wide blade is used to make the central component of the horizontal osteotomy.

Fig. 13.31 The saw blade is changed to a narrower one to complete the lateral components of the osteotomy.

Fig. 13.32 The caudal segment is advanced.

Fig. 13.33 The fixation plates have a step conformation to match the new contour of the anterior bone surface.

Fig. 13.34 The fixation plate is further contoured and fastened in place with four screws, two on either side of the osteotomy.

Fig. 13.35 A segment of bone can be removed to achieve reduction of anterior lower facial height.

Fig. 13.36 The wound is closed carefully incorporating both mucosa and mentalis muscle in each suture bite in order to assure proper alignment. Multiple interrupted chromic gut sutures are used.

Genioplasty using augmentation techniques

In current parlance, augmentation genioplasty usually refers to the implantation of alloplastic implants. Autogenous augmentation using bone or cartilage grafts is highly successful. However, unless the graft material is readily available because of a concomitant procedure being performed, one has to forego autogenous augmentation in favor of an osteotomy, which is often simpler. In extreme craniofacial cases, however, where the chin bone deficiency is too severe to reach the intended goals with an osteotomy, one may use bone or cartilage graft.

The two most common alloplastic materials used in augmentation genioplasty are silicone and porous polyethylene. While some literature suggests that silicone implants should be placed supraperiostially to diminish bone resorption, the senior author holds that a subperosteal plane should be considered for all implant types. Placing the implant in this plane and over the symphysis would minimize the soft tissue injury, dimpling and migration of the implant. Bone erosion will be also minimized if the implant is placed over the denser portion of the bone. Furthermore, if contracture should occur, the deeper location of the implant limits the deleterious affects on the soft tissue contour. The soft tissue response to augmentation genioplasty is 0.8 : 1.0 (Table 13.2).

Augmentation genioplasty can be performed under local anesthesia with sedation. A submental incision is favored over an intraoral approach because of the reduced risk of cephalad migration of the implant, dehiscence and infection. This incision also permits access to the anterior submental/cervical structures for lipectomy and platysma modification, which is commonly indicated in senescent patients requiring genioplasty.

The submental incision is placed 0.5 cm anterior to the natural submental crease. Prior to making an incision, the midline of the anterior chin is marked and extended across the incision. The area is infiltrated with xylocaine containing 1 : 200 000 epinephrine. The incision is made with a scalpel and carried through the soft tissues with electrocautery to the periosteum. The periosteum is incised and elevated. The midline mark on the skin is used to mark the underlying bone. A symmetric pocket is created just large enough to accommodate the implant using an Obwegeser elevator. The implant is inserted one side at a time and is positioned such that its midline is aligned with the midline of the chin as marked previously (Fig. 13.37). The wound is irrigated and the periosteum is closed using 5-0 monocryl for the periosteum and dermis and 6-0 fast-absorbable catgut for the skin. The soft tissue and skin are closed in layers. A tape dressing is applied. The patient will receive antibiotics perioperatively. An intraoral incision is employed when extended implants or mandibular angle implants are used. These are placed in the subperiosteal plane as well.

Fig. 13.37 Submental approach for augmentation genioplasty.

Optimizing outcomes

Outcomes are generally pleasing and improve chin appearance and overall facial harmony (Figs 13.38–13.41). Outcomes can be optimized as follows:

• Scrupulous preoperative evaluation: history, physical exam and soft-tissue cephalometric analysis of life-size photographs.

• Digital life-size photography to precisely plan the chin alterations.

• Utilization of osteotomy as often as possible to provide versatility to the technique and improve the cervico-mental angle.

• Leaving sufficient soft tissue on the gingival side of the incision to minimize lip ptosis and wound dehiscence.

• Placement of the implant in the subperiosteal plane when an implant is used.

• Protection of the soft tissue with malleable retractors to avoid nerve and soft tissue damage.

• Use of additional grafts under the labiomental groove, when an advancement over 10 mm is necessary, to avoid excessive deepening of in the labiomental groove.

Fig. 13.38 A patient with horizontal microgenia before (left) and following advancement genioplasty, secondary rhinoplasty, and submental lipectomy (right) on front view (above) and profi le (below).

Fig. 13.39 A patient with combined horizontal and vertical microgenia before (left) and following osseous genioplasty and submental lipectomy (right) on front view (above) and profi le (below).

Fig. 13.40 A patient with microgenia and aging face before (left) and following facial rejuvenation, submental lipectomy and osseous genioplasty (right) on front view (above) and profile (below).

Fig. 13.41 A patient before (left) and following reduction genioplasty with osteotomy (right) on front view (above) and profile (below).

Complications and Side Effects

Complications are rare. Nevertheless, the surgeon must understand their potential causes and management (Table 13.3).²⁷

Table 13.3 Complications of genioplasty and their management

Postoperative Care

The patient resumes eating the day of surgery. Liquids are advanced to a soft diet and then a regular diet according to the patient’s general tolerance of food within 24-48 hours. The patient is instructed to rinse with antiseptic mouthwash after eating and three times daily. Tooth brushing can be resumed the day of surgery, but the patient should be instructed to exercise caution when cleaning the area close to the incision. Oral antibiotics are prescribed for 5-7 days. The patient should avoid heavy exercise for 3 weeks following osteotomy. Foam type compressive tape dressing is removed in 2-3 days (Table 13.4).

Table 13.4 Postoperative care

Conclusion

Genioplasty is a relatively straightforward procedure with low morbidity and highly gratifying results. The use of digital life-size photographs with soft tissue cephalometrics facilitates precise surgical planning and execution. Understanding of the nature of the deformity and proper selection of the procedure are the keys to a successful outcome. Genioplasty also plays a pivotal role in achieving superior results when other disharmonies are being addressed with rhinoplasty, submental lipectomy or facial rejuvenation.