CHAPTER 51 OSSEOUS GENIOPLASTY
HARVEY M. ROSEN
Osseous genioplasty is an autogenous method for changing the size, or shape, or both of the mandibular symphysis. Although by strict definition it may involve merely recontouring the chin by burring away bone or by adding bone graft material, the term generally refers to an osteotomy of the anterior mandible in the horizontal (transverse) direction below the mental foramina (Figure 51.1A). The osteotomy was first described in 1942 by Hofer.1 The procedure remained rather obscure until 1964 when it was popularized by Converse and Wood-Smith.2 It is now the second most commonly performed osteotomy of the facial skeleton for both reconstructive and aesthetic reasons (second only to rhinoplasty).
Osseous genioplasty is frequently performed for two reasons: (a) versatility, the chin can be moved in any direction—sagittally, vertically, or transversely (Figure 51.1B–D); and (b) a receding chin or small mandible, or both, are common problems among white North Americans, occurring in approximately 5% of the population.3 When these factors are coupled with the emphasis that Western culture places on aesthetics and the belief that a well-defined jaw line characterizes an aggressive, self-confident individual, it is little wonder that this operation has grown in popularity. The ready availability of alloplastic material such as silastic, however, has prevented osseous genioplasty from becoming an operation that large numbers of plastic surgeons currently employ.
ALLOPLASTIC VERSUS AUTOGENOUS
The choice between alloplastic augmentation (chin implants) and osseous genioplasty for correction of the weak chin remains controversial. The proponents of alloplastic augmentation cite the technical ease, the relatively low risk of complications, and the ability to perform the procedure under a local anesthetic. Those who favor osseous genioplasty point out the extreme versatility of an osteotomy in correcting three-dimensional deformity.
In an effort to select the correct procedure, one should simply ask which procedure will provide the best correction for the particular patient. Certain factors are indisputable: (1) Chin implants can adequately correct mild to moderate volume deficiencies of the mandible at the level of the pogonion in the sagittal dimension. (2) Chin implants cannot correct vertical excess of the anterior mandible. (3) Chin implants are unreliable in correcting asymmetries of the anterior mandible in any plane of space. (4) Although chin implants can modestly increase the vertical dimension of the anterior mandible by covering its inferior border, this has significant potential for complications as the soft tissue in this area is relatively thin. (5) Provided that chin implants are positioned directly over the symphysis, as they should be, and not over the dental alveolus, the labiomental fold will increase in depth following chin implant placement.
FIGURE 51.1. A. Standard location and orientation of the advancement osseous genioplasty. Note that the osteotomy is placed well below the mental foramina to avoid injury to the inferior alveolar nerve. The osteotomy extends well posterior to the vicinity of the molar teeth. The angulation of this osteotomy allows forward advancement of the chin without any vertical changes. B. Simultaneous advancement and vertical reduction of the chin. Note that the two parallel osteotomies are performed with an intervening ostectomy. C. Simultaneous advancement and vertical elongation of the chin. The interpositional material typically employed is blocks of porous hydroxyapatite. D. Lateral shifting of the symphyseal segment to restore lower face symmetry.
Given these factors, the only appropriate candidates for chin implantation are those with a mild to moderate sagittal deficiency of the chin accompanied by a shallow labiomental fold. All other patients who request surgical alteration of the chin should be considered for osseous genioplasty.
One of the least mentioned, yet compelling, reasons to choose osseous genioplasty instead of alloplastic chin augmentation occurs when surgical revision is indicated. Osseous genioplasty is more amenable to revision because the soft-tissue chin has not been degloved and there is no scar capsule (as occurs in smooth implants) with which to contend. As a result, soft-tissue displacement closely follows skeletal displacement. Conversely, the soft-tissue response to removing a smooth implant, or to reducing its size, or to changing its position is unpredictable because the soft tissues have been degloved from the bone. In addition, the dead space created by the implant capsule, which does not fully collapse, fills with blood, creating more scar. Surgical excision of the capsule may cause mentalis muscle dysfunction with subsequent lower lip ptosis. Accordingly, the aesthetic consequences of removing or changing smooth chin implants are frequently undesirable.
Although a scar capsule may not form with porous implants, these implants can be very difficult to remove because of the soft-tissue ingrowth.
Preoperative evaluation of the osseous genioplasty patient includes a history and physical examination. The surgeon should ascertain the patient’s specific aesthetic complaints and objectives as they relate to the lower face, including any concerns about the height, the projection, and the symmetry in this area. Specific inquiries should be made into any history of orthodontic therapy, because such therapy may have been used to disguise an underlying class II malocclusion caused by a small mandible.
Physical examination should note the following five items:
1. The sagittal position of the pogonion relative to the lower lip and the remainder of the mid- and upper face. The lower lip, not the mid- or upper facial structures, determines the extent to which the chin should be brought forward.4 Consequently, the chin should not be brought forward any further than a vertical line dropped from the lower lip. When advancing the chin, the ratio of soft tissue to skeletal displacement is generally 1:1. If the lower lip is recessive, as it may be in many individuals with small mandibles who are seeking chin enlargement, one must be willing to accept a residual degree of sagittal weakness of the lower face relative to the mid- and upper face. This is aesthetically preferable to a chin that is advanced beyond the lower lip, which invariably results in a bizarre, artificial appearance. Undercorrection in the sagittal dimension is always preferable to overcorrection.
2. A qualitative assessment of the height of the lower face as it relates to the midface. In a patient with vertical excess of the lower face, one has the option to reduce the vertical height of the chin. This can be accomplished by two parallel osteotomies with an intervening ostectomy or a steeply oblique bone cut that allows the chin to be advanced and superiorly repositioned.
3. The symmetry of the lower face. Osseous genioplasty presents the surgeon with the opportunity to laterally shift the symphyseal segment either to the right or to the left to achieve a symmetric lower face. Similarly, the chin can be vertically elongated or shortened in an asymmetric fashion to correct vertical asymmetry.
4. The depth of the labiomental fold. Sagittal advancement or vertical shortening, or both, of the symphyseal segment results in deepening of the labiomental fold.5 Conversely, vertical lengthening of the chin tends to efface or soften the fold. Accordingly, individuals with a normal or exceedingly deep fold who undergo advancement of the chin also should be evaluated for vertical elongation. This should be considered in a person with a short lower face and in a patient with normal height of the lower face, but never in a patient with excessive height in the lower face. The individual who has a combination of a long lower face and a deep labiomental fold is never a candidate for chin surgery, and such a patient should be offered a more extensive orthognathic correction.5
5. Examination of the occlusion. The majority of individuals who request aesthetic enlargement of the chin have class II skeletal deformities secondary to a small mandible.5 This is a tip-off that coexisting problems such as abnormalities of lower face height and labiomental fold depth may be present in addition to a “weak” chin. It is important to remember that prior orthodontic treatment can convert a class II malocclusion into a class I occlusion but this does not correct the underlying skeletal problems.
Although the extent of soft-tissue movement closely follows that of skeletal displacement when advancing, shortening, or lengthening the chin, soft-tissue response to posteriorly repositioning of the chin is, at best, 0.5 to 1. Surgical efforts to correct an excessively prominent chin are not as predictable as those performed to correct a small chin.
Radiographic evaluation of the chin should include a Panorex radiograph if periapical pathology of the anterior mandibular teeth is suspected. Any preexisting dental pathology in this area is an absolute contraindication to chin surgery. In addition, one may want to evaluate the vertical dimension between the apices of the incisor roots and the inferior border of the mandible when correcting a short chin. It is important that enough room exists both to perform the osteotomy and to apply fixation devices without risk to the roots of these teeth.
Although reports exist describing osseous genioplasty under local anesthesia with intravenous sedation,5 it is best undertaken under general anesthesia with orotracheal or nasotracheal intubation and full protection of the airway. Hemostasis is facilitated by infiltration with a dilute epinephrine solution. The soft-tissue incision is placed at least 1 cm away from the depth of the mandibular buccal sulcus onto the lower lip and is 2 to 3 cm in length. The mucosa and submucosa are incised, bringing the mentalis muscle and its median raphe into view. Once these muscles are very superficially incised, the angle of the soft-tissue incision changes so that it is parallel to the mucosa of the lip. This direction is maintained until the anterior mandibular surface is reached, leaving a large amount of mentalis muscle attached to the mandible for later muscle reapproximation. A subperiosteal dissection of the symphysis is performed. The dissection is continued inferiorly only far enough to allow exposure for performing the osteotomy and for applying fixation devises. Complete degloving of the symphysis is not recommended because of the unpredictable reattachment of the soft tissues to the bone and the potential risk for the development of soft-tissue ptosis, that is, a witch’s chin.7 Exposure is continued laterally so that both mental nerves are identified. Posterior dissection is carried to the inferior border of the mandible directly below the molar roots.
Once the soft-tissue dissection is completed, a fissure burr scores a vertical mark in the midline chin, allowing it to be appropriately positioned in the transverse dimension. The reciprocating saw is used to perform the horizontal osteotomy at least 4 mm below the mental foramina to protect the inferior alveolar nerves. As previously mentioned, the osteotomy is carried as far posteriorly as possible to allow for a generous volume of skeletal displacement. This provides for natural-looking results and avoids waist lining and excessive visibility of the inevitable step in the inferior border of the mandible. Cortical cuts should be completed with the reciprocating saw, avoiding unnecessary prying downward of the symphyseal segment, which may cause fracturing. Following mobilization of the symphysis, it might be necessary to detach the anterior belly of the digastric muscles from the lingual surface if extensive anterior dislocation is anticipated. After full mobilization is achieved, fixation devices are applied to hold the chin segment in the desired location. Although plate and screws are popular, it is perfectly acceptable to use wire fixation.
If vertical shortening of the chin is desired, it is usually accomplished by performing two parallel horizontal osteotomies and removing the intervening segment of bone. If vertical elongation is desired, it is most often done by interposing blocks of hydroxyapatite into the osteotomy gaps created by inferior repositioning of the symphysis.
Following fixation, the wound is copiously irrigated with diluted povidone-iodine (Betadine) solution and closed in layers. The mentalis muscle is repaired using interrupted sutures to help avoid soft-tissue ptosis and subsequent development of a witch’s chin.7 The mucosa is repaired using interrupted 3-0 chromic sutures. By placing the incision well out onto the lower lip, there is sufficient soft tissue to close without tearing the tissues. This helps minimize subsequent wound contamination and possible infection. No dressings are applied.
The following patient examples illustrate the versatility of the osseous genioplasty.
The patient (Figure 51.2) is a 35-year-old woman with a small mandible, an increased lower face height, and a modest component of lip strain. As a result, the soft-tissue chin pad is superiorly dislocated, causing effacement and shallowness of the labiomental fold. Surgical correction involves advancement and vertical shortening of the chin. The segment was advanced 8 mm and shortened 5 mm. A rhinoplasty was also performed. Note that as the chin is advanced the labiomental fold deepens with improved definition. The lip strain has been eliminated. The chin has been advanced no further than the lower lip.
FIGURE 51.2. A 35-year-old woman with a small mandible and increased lower face height. A, B. There is lip strain, with superior dislocation of the soft-tissue chin pad and a shallow labiomental fold. Surgical correction will effect an 8-mm advancement of the chin and a 5-mm reduction in its height. Simultaneous rhinoplasty will be performed. C, D. Postoperatively, the lip strain has been eliminated and the labiomental fold has been deepened. Note that the chin has been advanced no further than the most anterior position of the lower lip. (From Rosen HM. Aesthetic refinements in genioplasty: the role of the labiomental fold. Plast Reconstr Surg. 1991;88:760, with permission.)
This 28-year-old man (Figure 51.3) complained of having a small chin. Physical examination demonstrated that he had a small mandible and a class II, deep bite malocclusion. In addition to a lack of projection of the chin, there was decreased height of the lower face relative to the midface and an exaggerated, deepened labiomental fold. Surgical planning involved a 6-mm advancement and 6-mm lengthening of the chin. In the postoperative views, note the softening of the labiomental fold and apparent decrease in its depth. Note again that the chin is advanced no further than the most anterior position of the lower lip.
In a recent report of a large series of patients undergoing osseous genioplasty by three experienced craniomaxillofacial surgeons, the complication rate was low.8 Lower lip paresthesia occurred in 5.5% of the patients. Soft-tissue infection was reported in 3% of patients.
Although not reported as a complication, the most frequent problem associated with osseous genioplasty is the undesirable aesthetic result. Such an outcome is caused by errors in both treatment planning and technique. The most commonly committed error in treatment planning is overadvancement of the symphyseal segment, resulting in an unnatural, bizarre appearance, with the chin well in advance of the lower lip. It bears repeating that the osseous genioplasty is a powerful tool and that modest advancement of the chin goes a long way. When in doubt about the extent of advancement, one should err on the side of conservatism and undercorrect in the sagittal dimension.
FIGURE 51.3. A 28-year-old man complaining of a small chin. Physical examination demonstrated a class II malocclusion with deficient sagittal projection of the chin as well as decreased height of the lower face. A, B. In addition, there is a deepened labiomental fold. Surgical planning included a 6-mm advancement and 6-mm elongation of the chin. C, D. The postoperative views demonstrate an increase in the height of the lower face and an apparent decrease in the depth of the labiomental fold. Again, the chin was advanced no further than the most anterior position of the lower lip. (From Rosen HM. Aesthetic refinements in genioplasty: the role of the labiomental fold. Plast Reconstr Surg. 1991;88:760, with permission.)
The most commonly encountered aesthetic problem relative to the surgical technique is failure to extend the osteotomy cut far enough posteriorly. This can result in an hourglass deformity with excessive tapering of the mandible in the area immediately posterior to the osteotomy. This can be largely avoided if the osteotomy cut is extended back to the molar teeth, as it is placed in an area where abundant soft tissue is present to mask any notching of the inferior mandibular border.
The osseous genioplasty represents the most versatile procedure that the plastic surgeon has available to enhance the balance and proportion of the lower face. It is a powerful tool that can yield dramatic results if the surgeon performing the procedure knows that it cannot change the sagittal position of the lower lip. It behooves plastic surgeons to become familiar and comfortable with the procedure so that the alternative—alloplastic chin augmentation—will not be used in patients who would be better treated by osseous genioplasty.
1. Hofer D. Die osteoplastiche verlaegerund des unterkiefers nach von Eiselberg bie mikrogenie. Dtsch Zahn Mund Kieferheilkd. 1957;27:81.
2. Converse JM, Wood-Smith D. Horizontal osteotomy of the mandible. Plast Reconstr Surg. 1964;34:464.
3. Bell WH, Proffit WR, White P, eds. Surgical Correction of Dentofacial Deformities. Philadelphia, PA: WB Saunders; 1980:685.
4. Rosen HM. Aesthetic guidelines in genioplasty: the role of facial disproportion. Plast Reconstr Surg. 1995;95:463.
5. Rosen HM. Aesthetic refinements in genioplasty: the role of the labiomental fold. Plast Reconstr Surg. 1991;88:760.
6. Spear SL, Mausner ME, Kawamoto HK. Sliding genioplasty as a local aesthetic outpatient procedure: a prospective two center trial. Plast Reconstr Surg. 1987;80:55.
7. Zide BM, McCarthy JG. The mentalis muscle: an associated component of chin and lower lip position. Plast Reconstr Surg. 1989;83:413.
8. Greenberg ST, Pan FS, Bartlett SP, et al. Complications of osseous genioplasty. Proc Northeastern Soc Plastic Surg. 1985;92.