CHAPTER 50 FACIAL SKELETAL AUGMENTATION WITH IMPLANTS
MICHAEL J. YAREMCHUK AND CHAD R. GORDON
The morphology of the facial skeleton is a fundamental determinant of facial appearance. Facial skeletal augmentation is usually accomplished with alloplastic materials. Implants can be used to restore or create contour during reconstruction of congenital, posttraumatic, or postablative deformities. They are useful adjuncts and, sometimes, alternatives to orthognathic surgery in patients with corrected or normal occlusion, respectively. Most often, facial skeletal augmentation is performed electively to improve facial aesthetics (Figure 50.1).
Physical examination is the most important element in preoperative assessment and planning. Reviewing life-size frontal and lateral photographs with the patient is useful when discussing aesthetic concerns and goals. Although cephalometric radiograph analysis can be helpful in the planning, the size and position of the implants are largely aesthetic judgments. Computerized tomographic (CT) data with subsequent physical model reconstruction can be particularly useful in planning the procedure or designing and fabricating implants specific for an individual patient.
Although often referenced in texts discussing facial skeletal augmentation, neoclassical canons describing ideal facial proportions have a limited role in surgical evaluation and planning because they are arbitrary. When the facial dimensions of normals and those deemed more attractive than normal were compared with artistic ideals, it was found that some theoretic proportions are never found, and others are one of the many variations.1,2 For these reasons, we have found it more useful to use the anthropometric measurements of normals to guide our gestalt for the selection of implants for facial skeletal augmentation.
In planning facial skeletal augmentation, it is important to realize that small increases in skeletal projection have a powerful impact on facial appearance. It is emphasized to the patient during the preoperative consultation that all faces are asymmetric. If unrecognized preoperatively, an asymmetric postoperative result usually may be interpreted by the patient as a technical error by the surgeon.
Virtually all aesthetic facial skeletal augmentation is achieved with alloplastic implants. The use of synthetic materials avoids donor site morbidity and vastly simplifies the procedure in terms of time and complexity. Implant materials used for facial skeletal augmentation are biocompatible, that is, they have an acceptable interaction between the material and the host. Because the host has little or no enzymatic ability to degrade the implant material, the implant tends to maintain its volume and shape. Likewise, the implant has a minimal and predictable effect on the host tissue that surrounds it. This type of relationship is an advantage over the use of autogenous bone which, when revascularized, will be remodeled to varying degrees, thereby changing volume and shape.3
The presently used alloplastic implants used for facial reconstruction do not have a toxic effect on the host.4 The host responds to these materials by forming a fibrous capsule around the implant, thereby isolating the implant. The surface of the implant determines the nature of the capsule. Smooth implants result in the formation of smooth-walled capsules. Porous implants allow varying degrees of soft-tissue ingrowth, which results in a less-dense and less-defined capsule. Clinical experience has shown that porous implants have fewer tendencies to erode underlying bone and fewer tendencies to migrate as a result of overlying soft-tissue mechanical forces. These attributes are presumably due to the fibrous incorporation associated with porous implants as opposed to the fibrous encapsulation typical of smooth implants.
The most commonly used and commercially available materials today for facial skeletal augmentation are solid silicone, polytetrafluoroethylene, and porous polyethylene. The silicone rubber used for facial implants is a vulcanized form of polysiloxane, which is a polymer created from interlocking silicone and oxygen with methyl side groups. Silicone is derived from silicon, a semimetallic element that in nature combines with oxygen to form silicon dioxide, or silicone. Beach sand, crystals, and quartz are silica. The advantages of solid silicone are that it is easily sterilizable by steam or irradiation, it can be carved easily with either a scissor or scalpel, and it can be stabilized with a screw or a suture. There are no known clinical or allergic reactions. Because it is smooth, it can be removed quite easily. The disadvantages of silicone implants include their tendency to cause resorption of the bone underlying it, the potential to migrate if not fixed, and the likelihood for the implant and its fibrous capsule to be visible when placed under a thin soft-tissue cover.
Polytetrafluoroethylene. Polytetrafluoroethylene has a carbon-ethylene backbone to which are attached four fluorine molecules. It is chemically stable, has a nonadherent surface, and, because it is not cross-linked, is flexible. Extensive experience has been accumulated with polytetrafluoroethylene (Gore-Tex; WL Gore, Flagstaff, AZ) for vascular prostheses, soft-tissue patches, and sutures. A variety of preformed implants are available for both subdermal and subperiosteal placement. Preformed implants are made with a pore size between 10 and 30 µm. The porosity allows for some soft-tissue ingrowth, for less fibrous encapsulation, and for less tendency to migrate as compared with smooth-surfaced implants. It is easily sterilizable, smooth enough to be maneuvered easily through soft tissues, and can be fixed to underlying structures with sutures or screws.
Polyethylene. Polyethylene is a simple carbon chain of ethylene monomer. The high-density variety—Medpor (Porex, Newnan, GA) and SynPOR (Synthes, West Chester, PA)—is used for facial implants because of its high tensile strength. Although chemically similar to polytetrafluoroethylene, polyethylene has a much firmer consistency that resists material compression yet permits some flexibility. Its intramaterial porosity between 125 and 250 µm allows more extensive fibrous ingrowth as compared with polytetrafluoroethylene. Soft-tissue ingrowth lessens the implant’s tendency to migrate and to erode underlying bone. Its firm consistency allows it to be easily fixed with screws and to be contoured with a scalpel or power equipment without fragmenting. A disadvantage of its greater porosity is that it allows soft tissues to adhere to it, making placement more difficult and requiring a larger pocket than is required for smoother implants. Soft-tissue ingrowth into the larger pores also makes implant removal more difficult.
FIGURE 50.1. A 26-year-old male who in two operations had multiple implants placed. Implant augmentation of the infraorbital rim, paranasal, malar, and mandibular body was performed. In addition, rhinoplasty, midface lift, and lateral canthopexies were also performed. A.Preoperative; B. Diagrammatic representation of operation; C. Postoperative. (From Yaremchuk MJ. Facial skeletal reconstruction using porous polyethylene implants. Plast Reconstr Surg. 2003;111:1818, with permission.)
Requisites of Implant Shape, Positioning, and Immobilization
Shape. The superficial surface of the implant determines the new skeletal morphology. Its posterior surface should mold to the bone to which it is applied. Gaps between the bone and the implant result in unpredictable increases in augmentation. The implant margins must taper imperceptibly into the native skeleton so that they are neither visible nor palpable.
Positioning. Although some surgeons prefer to place implants in a soft-tissue pocket (supraperiosteal), clinical experience has led to a strict policy of subperiosteal placement. A subperiosteal pocket involves a dissection that is safe to nerves and is relatively bloodless. It allows optimal visualization of the skeleton and therefore the opportunity for precise augmentation.
The size of the pockets is determined by the type of implant used and its method of immobilization. The long-standing teaching when using smooth silicone implants is to make a pocket just large enough to accommodate the implant so as to guarantee its position. Porous implants require a larger pocket because they adhere to the soft tissue during their placement. When using smooth or porous implants, I dissect widely enough to have a perspective of the skeletal anatomy being augmented, which allows precise and symmetric implant positioning.
Immobilization. Many surgeons stabilize the position of the implant by suturing it to surrounding soft tissues or by using temporary transcutaneous pullout sutures. Screw fixation of the implant to the skeleton has several benefits. It prevents movement of the implant. Because each facial skeleton has a unique and varying surface topography, portions of an implant may not conform to the bone, leaving gaps between the implant and the skeleton. This results in unpredicted increases in augmentation and distortions of the desired facial shape. Screw fixation assures application of the implant to the bone. Screw fixation also allows for final contouring of the implant in position. This final contouring is particularly important where the edge of the implant interfaces with the skeleton (Figure 50.2). Step-offs between the implant and the skeleton may be palpable and visible.
FIGURE 50.2. Representation of a preferred technique for chin augmentation. Through a submental approach, a two-piece porous polyethylene implant is fixed to the skeleton with titanium screws. This maneuver immobilizes the implant and obliterates any gaps between the implant and the underlying bone. The implant is being contoured to provide an imperceptible implant-native mandible transition.
Facial skeletal augmentation can be performed under local or general anesthesia and is routinely performed on an outpatient basis. I prefer to perform most facial skeletal surgery under general endotracheal anesthesia because most facial implants are placed either in the malar midface or along the mandible, which requires a combination of intraoral incisions. Endotracheal intubation assures protection of the airway and the optimal antiseptic preparation of the oral cavity. Patient positioning and exposure for implant placement are also optimized when the airway is controlled. The surgical site is infiltrated with a solution containing Marcaine for postoperative pain control and epinephrine to minimize bleeding.
AREAS FOR AUGMENTATION
The mid and lower face are areas most often altered with implants.
Implants are specifically designed to augment the malar, paranasal, and infraorbital rim areas.
Malar. Patients who seek malar augmentation may have normal anatomy but desire greater prominence of their middle malar prominence while others have midface skeletal deficiency.5
Malar augmentation can be performed through intraoral, coronal, or eyelid incisions. An intraoral approach is preferred. An upper buccal sulcus incision is made far enough from the apex of the sulcus so that sufficient labial tissue is available on either side for a secure closure. Division of the lip elevators is avoided. Taking care to identify the infraorbital nerve, subperiosteal dissection is carried over the malar eminence and onto the zygomatic arch, almost up to the zygomaticotemporal suture. Surgeons who use smooth silicone implants often assure the position of the implant by using suture suspension fixation.
The position of both smooth and porous implants can be certain with screw fixation of the implant to the skeleton. Patients who are dissatisfied with malar implant surgery frequently complain that the implants are too large, are placed asymmetrically, or are placed too far laterally, thereby exaggerating midface width.
Paranasal. A relative deficiency in lower midface projection may be congenital or acquired, particularly after cleft surgery and trauma. Patients with satisfactory occlusion and midface concavity are candidates for skeletal augmentation. Implantation of alloplastic material in the paranasal area can simulate the visual effect of Le Fort I advancement (Figure 50.3).6 Paranasal augmentation is done through an upper gingival buccal sulcus incision made just lateral to the piriform aperture. Placement of incisions directly over an implant is avoided.
Infraorbital Rim. Augmentation of this area is useful for patients with deficiencies of the upper midface and infraorbital rim area. This skeletal deficiency is often responsible for overly prominent eyes.Infraorbital rim augmentation can effectively reverse the “negative” vector of midface hypoplasia (Figures 50.1 and 50.4).7
The infraorbital rim and adjacent anatomy should be exposed sufficiently to assure ideal implant placement, smooth implant facial skeleton transition, and screw fixation. Subciliary skin or skin muscle flap incisions provide adequate exposure. A transconjunctival incision alone provides limited exposure and often requires concomitant intraoral access.
FIGURE 50.3. A 26-year-old woman underwent an aesthetic rhinoplasty and paranasal augmentation. A. Preoperative. B. Postoperative. C. Artist’s rendition of implant placement.
Mandibular Augmentation. Each of the anatomic areas of the mandible—the chin, body, angle, and ramus—is amenable to augmentation.
The ideal facial profile portrays a convex face, with the upper lip projecting approximately 2 mm beyond the lower lip and the lower lip projecting approximately 2 mm beyond the chin.8 The projection of the chin should be interpreted in the context of the surrounding facial features, including the projection of the nose, the relationship to the lips, and the depth of the labiomental sulcus.
Implant Design. Early implant designs augmented the mentum only and often created a stuck-on appearance as a result of failure of the lateral aspect of the implant to merge with the anterior aspect of the mandibular body. “Extended” chin implants first popularized by Flowers9 and Terino10 have lateral extensions that enable the chin implant to better merge with more lateral mandibular contours. Myriad designs are available that give great latitude in the desired effect. Extended porous polyethylene implants that have limited flexibility are designed in two pieces to allow their placement through a limited incision. The two pieces connected by a small bar in the midline convey an additional advantage.11 The central connecting bar can act as a hinge allowing the arc of the implant to be adjusted so that the inferior border of the implant can follow the inferior border of the mandible. This is usually not possible with an extended one-piece chin implant, often resulting in undesired outcomes.
FIGURE 50.4. Globe-orbital rim relationships have been categorized by placing a line or “vector” between the most anterior projection of the globe and the malar eminence and lid margin. (Left) Positive vector relationship. In the youthful face with normal globe-to-skeletal rim relations, the cheek mass supported by the infraorbital rim lies anterior to the surface of the cornea. The position of the cheek prominence beyond the anterior surface of the cornea is termed a positive vector. (Center) Negative vector relationship: In patients with maxillary hypoplasia, the cheek mass lies posterior to the surface of the cornea. The position of the cheek prominence beyond the anterior surface of the cornea is termed a negative vector. (Right) “Reversed” negative vector relationship: Alloplastic augmentation of the infraorbital rim can reverse the negative vector.
Submental Incision. Ideal results from alloplastic augmentation of the chin are not routinely obtained. Problems result from implants that merge poorly with the mandibular body; implants with posterior surfaces that are inappropriate for the tilt of the anterior surface of the chin; asymmetric implant placement; implant migration; and morbidity from surgical exposure. Placing two-piece extended implants through submental incisions assures ideal implant placement and minimizes soft-tissue morbidity. The incision is carried onto the mentum and a subperiosteal pocket is created that avoids disturbing the mentalis muscle origin and allows easy identification of the mental nerves (Figure 50.2).
Intraoral Incision. In patients in whom a submental scar may be objectionable, an intraoral incision is employed. An approximately 2 cm transverse incision is made 1 cm above the buccal sulcus in the midline. When the mentalis muscles are encountered, these muscles are neither divided nor stripped from the mandible, but are separated in the midline to access the mentum where a subperiosteal pocket is created. Placement of an extended chin implant through a midline intraoral approach alone is difficult. This intraoral exposure may result in division or damage to the mentalis muscles, damage to the mental nerve, and improper positioning of the lateral extensions of the implants. To assure implant placement, particularly of its lateral extensions, sulcus incisions 1.5 to 2 cm long are made lateral to the mental nerve. The mental foramen usually lies halfway between the top and the bottom of the mandible and directly between the two premolars. Once the implant is positioned, it is immobilized with sutures or screws.
Implant Augmentation versus Sliding Genioplasty
Sliding genioplasty involves a horizontal osteotomy of the mandible approximately 4 mm beneath the mental foramen. A now free chin point that can be moved in any direction is positioned as desired, usually anteriorly to increase chin projection. It has certain advantages over implant augmentation of the chin. First, the chin point can be lowered after osteotomy to increase the vertical height of the chin. Vertical elongation may efface the deep labiomental sulcus affecting some patients. Second, the chin point advancement stretches the attached suprahyoid muscles, thereby decreasing submental fullness to improve submental contour and, in certain individuals, may improve their compromised airways.
The major disadvantage intrinsic to sliding genioplasty is the unnatural bony and border contours that accompany the selective movement of the chin point. The contour may have a poor transition, resulting in the stuck-on appearance of the chin—much like a large button chin implant. There are also step-offs at the osteotomy sites along the mandibular body. The notchings or indentations are particularly detrimental to those who have existing prejowl sulci. Furthermore, sliding genioplasty requires considerable facility in bone carpentry. For example, an unanticipated obliquity in the horizontal osteotomy can either lengthen or shorten the vertical height of the chin after advancement.
Ramus and Body. Alloplastic augmentation of the mandibular ramus and body can have a dramatic impact on the appearance of the lower third of the face.12 Three different patient populations are candidates. One group has mandibular dimensions that relate to the upper and middle thirds of the face within the normal range. These patients desire a wider lower face with a well-defined mandibular border. Patients in this treatment group often present with a desire to emulate the appearance of models, actors, and actresses who have well-defined, angular lower faces. This patient group benefits from implants designed to augment the ramus and posterior body of the mandible and, in so doing, increase the bigonial distance.
A second subset of patients have skeletal mandibular deficiency. These patients may have normal occlusion or may have had their malocclusion treated with orthodontics alone. The skeletal anatomy associated with mandibular deficiency that can be camouflaged with implants includes the obtuse mandibular angle with steep mandibular plane and decreased vertical and transverse ramus dimensions. The addition of an extended chin implant will camouflage the poorly projecting chin (Figure 50.5).
A third group of patients who benefit from alloplastic augmentation of the mandible are patients who have had their Class II dental malocclusion due to mandibular deficiency corrected by sagittal split osteotomy with advancement of the occlusal segment. This procedure splits or separates the tooth-bearing symphysis and adjacent bodies from the non–tooth-bearing rami. Requisites for positioning the resultant anterior and posterior segments to improve occlusion, allow bone healing, and continue joint function may result in displeasing postoperative contour. The advancement of the tooth-bearing segment inevitably creates a contour irregularity at the site of the body osteotomy. This area of narrowing may be visible and even disfiguring, in certain individuals. Positioning of the posterior segment requires that the condyle be seated in the glenoid fossa and that there be sufficient contact with the occlusal segment to allow bone healing. When the sagittal osteotomies are less than ideal, the location of bone fixation is compromised and, hence, the position of the ramus. This may result in aesthetically displeasing ramus height, width, or asymmetry. Mandible implants can be used to improve contour in these patients.13 Custom implants designed from the data obtained from CT scans are particularly useful to correct these deformities (Figure 50.6).
FIGURE 50.5. A 32-year-old woman with mandibular deficiency and corrected occlusion underwent chin and mandible implant augmentation. Preoperative (A) and postoperative (B, 2 years) oblique views. C. The artist has drawn the underlying skeleton and implant applications.
FIGURE 50.6. A 50-year-old woman underwent custom mandible implants designed from computerized tomographic data to correct mandibular deficiency and irregularity after sagittal split osteotomy.
Operative Technique. A generous intraoral mucosal incision is made at least 1 cm above the sulcus on its labial side. The anterior ramus and body of the mandible are freed from their soft tissues. The mental nerve is visualized as it exits its foramen. It is important to free both the inferior and posterior borders of the mandible of soft-tissue attachments. As determined by preoperative assessment, the implant is trimmed prior to its placement on the mandible. To assure the desired placement of the implant and its application to the surface of the mandible, the implant is fixed to the mandible with titanium screws. The incision is closed in two layers with absorbable sutures. Care is taken to evert the mucosal edges. A suction drain is tunneled through the subcutaneous tissues to exit in the postauricular area.
Implants Used to Camouflage Soft-Tissue Depressions
The implants discussed in this chapter are designed to increase the surface projection of the facial skeleton. Certain authors have used implants placed on the facial skeleton to disguise overlying soft-tissue volume inadequacy, usually caused by involutional changes. These include the submalar, prejowl, and tear trough implants. Augmentation of the skeleton to compensate for a soft-tissue deficiency should be conservative. Skeletal augmentation does not give the same visual effect as the soft-tissue augmentation. Similarly, soft-tissue augmentation beyond 1 or 2 mm provides a different visual effect than skeletal enlargement. For example, a chin point augmented with fat to increase projection by 5 mm reads as a fatty chin pad, not as a more projecting chin.
Concavity in the temporal area reflects a deficiency in the bulk of the temporalis muscle or the overlying temporal fat pad. It may be caused by senescence, low body fat, exaggerated adjacent skeletal or soft-tissue contours, idiopathic progressive atrophy, or postsurgical atrophy. We use polymethylmethacrylate (PMMA) to fill depressions in the temporal area. In instances when no previous surgery has been performed or when the temporal area has served as a dissection plane for surgery in adjacent areas (e.g., subperiosteal facelift), the implant material is placed beneath the temporal muscle through a limited incision in the hair-bearing scalp.
When previous reconstructive surgery has been performed in the temporal area, the scars from previous incisions are used for access and the PMMA is placed over the altered temporalis muscle and its neighboring fossa. Titanium screws are placed along the lateral orbital rim preventing implant motion. These operative techniques using PMMA have been reliable, long lasting, and relatively free of complications.14
There are no scientific data to document the complication rate related to facial skeletal augmentation. Prospective studies that control for surgical technique, implant site, patient selection, and follow-up time do not exist. Because all the biomaterials commonly used for facial skeletal augmentation are biocompatible, complications are usually technique related—improper implant size, contour, or placement.
When infection occurs, the most reliable treatment is implant removal.
Augmentation of the facial skeleton with alloplastic materials is a powerful way to alter facial appearance. Virtually any area of the facial skeleton can be augmented. Requisites for success include implants of appropriate size and shape, adequate soft-tissue cover, and careful subperiosteal dissection during exposure and implant placement.
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