Introduction

Augmentation is the predominant means of aesthetic contouring of the facial skeleton in non-Asian populations. Conceptually, autogenous bone would be the best material for augmentation, because it has the potential to be revascularized and, then, incorporated into the facial skeleton. In time, it could be biologically indistinguishable from the adjacent native skeleton. Practically, the use of autogenous bone is limited. The morbidity, time and hospital costs associated with autogenous bone graft harvest can be significant. Furthermore, the inevitable resorption and the poor handling characteristics of autogenous bone grafts also limit the quality and predictability of the aesthetic result. For these reasons, almost all facial skeletal augmentation is done with alloplastic implants. A diagrammatic survey of the facial skeletal areas amenable to augmentation with alloplastic implants is presented in Fig. 14.1.

Fig. 14.1 A diagrammatic survey of the alloplastic implants used for facial skeletal enhancement. Anatomic areas include the infraorbital rim, malar, pyriform aperture, chin as well as the mandibular body and ramus.

Indications

• Facial skeletal augmentation is most often done to enhance facial appearance in patients whose skeletal relationships are ostensibly within the normal range. These patients want more definition and angularity to their appearance. Other patients desire to “balance” their facial dimensions.

• Craniofacial deformities which are disfiguring and are of functional consequence to vision, breathing, and mastication, usually require skeletal osteotomies and rearrangement as treatment. In patients with less severe midface or mandibular hypoplasia, occlusion is normal or has been compensated by orthodontics. These patients have neither respiratory nor ocular compromise. In these patients, the appearance of skeletal osteotomies and rearrangements can be simulated through the use of facial implants. Diagrammatic representations of how implant surgery can mimic the appearance of skeletal osteotomies are shown in Figs 14.2 and 14.3.

Fig. 14.2 Diagrams show how multiple implant augmentation of the midface skeleton can simulate the visual appearance of LeFort III osteotomy and advancement without altering dental occlusion. A, Illustration of midface concavity and Class III malocclusion. B, Osteotomy and advancement at the LeFort III level provides midface projection and Class I occlusion. C, Illustration of midface concavity and Class I occlusion. D, Multiple midface implants provide visual effect of LeFort III osteotomy and advancement but does not alter occlusion.

Fig. 14.3 Diagrams show how multiple implant augmentation of the mandible can simulate the visual appearance of of sagittal split osteotomy and horizontal osteotomy of the chin without altering dental occlusion. A, Mandibular deficiency with Class II occlusion. B, After sagittal split osteotomy with horizontal osteotomy and advancement of the chin to increase chin projection. Note that the occlusion has been corrected from Class II to Class I. C, Mandibular deficiency with Class I occlusion. D, The visual effect of sagittal split osteotomy and horizontal osteotomy of the chin with advancement has been simulated with mandible and chin implants. Note that the Class I occlusion is unchanged. Notice also that the border regularities inherent with skeletal osteotomies are avoided when implants are used.

Preoperative Evaluation

Surgical Planning

For most reconstructive problems, surgery is performed to return the involved area to its original appearance, or, if that is not possible, to one that is symmetric and accepted as normal. When alloplastic implants are used to make the face more attractive, the aesthetic goal is more arbitrary. Because implant augmentation of the facial skeleton results in measurable changes in facial dimensions and proportions, it is intuitively advisable and appropriate to use facial measurements to evaluate the face and to guide surgery.

Facial anthropometries and neoclassical canons

For purposes of painting and sculpture, Renaissance scholars and artists formulated ideal proportions and relations of the head and face. These were largely based on classical Greek canons. Although usually referenced in texts discussing facial skeletal augmentation, neoclassical canons have a limited role in surgical evaluation and planning, because they are based on idealizations. When the dimensions of normal males and females were evaluated and compared to these artistic ideals, it was found that some theoretic proportions are never found, and others are one of many variations found in healthy normals, or those determined more attractive than normals.^1,2 The neoclassical canons do not allow for the facial dimensions that are known to differ with sex and age. Most of these canons of proportion (e.g. the width of the upper face is equal to five eye widths), are interesting but hold for few individuals and cannot be obtained surgically or, if obtainable, only with extremely sophisticated craniofacial procedures. For these reasons, we have found it more useful to use the anthropometric measurements of normal individuals to guide our Gestalt in the selection of implants for facial skeletal augmentation (Fig. 14.4).³ Normal dimensioned faces are intrinsically balanced. That is, the relations between the various areas of the face relate to one another in a way that is not distracting to the observer. By comparing a patient’s dimensions to the average, the surgeon has some objective basis as to what anatomic area may be amenable to augmentation, and by how much.

Fig. 14.4 Frontal and lateral views of female and male faces drawn from average anthropometric measurements for 21 year old North American Caucasians. Measurements are in millimeters. A, Frontal view female. B, Frontal view male. C, Lateral view female. D, Lateral view male.

Alloplastic Materials

Implant materials used for facial skeletal augmentation are biocompatible – that is, there is an acceptable reaction between the material and the host. In general, the host has little or no enzymatic ability to degrade the implant with the result that the implant tends to maintain its volume and shape. Likewise, the implant has a small and predictable effect on the host tissues that surround it. This type of relationship is an advantage over the use of autogenous bone or cartilage which, when revascularized, will be remodeled to varying degrees, thereby changing volume and shape.

The presently used alloplastic implants used for facial reconstruction have not been shown to have any toxic effects on the host.⁴ The host responds to these materials by forming a fibrous capsule around the implant, which is the body’s way of isolating the implant from the host. The most important implant characteristic that determines the nature of the encapsulation is the implant’s surface characteristics. Smooth implants result in the formation of smooth-walled capsules. Porous implants allow varying degrees of soft tissue ingrowth that results in a less dense and defined capsule. It is a clinical impression that porous implants, as a result of fibrous incorporation rather than encapsulation, have a lower tendency to erode underlying bone or migrate due to soft tissue mechanical forces and, perhaps, are less susceptible to infection when challenged with an inoculum of bacteria. The most commonly used, commercially available materials today for facial skeletal augmentation are solid silicone, and porous polyethylene -Medpor (Porex, Fairborn, GA). Eppley⁵ has summarized the attributes of these materials.

Requisites of Implant Shape, Positioning, and Immobilization

Immobilization

Facial implants should be immobilized. Many surgeons stabilize the position of the implant by suturing it to surrounding soft tissues or by using temporary transcutaneous pull-out sutures. Screw fixation of the implant to the skeleton is preferred. Screw fixation prevents any movement of the implant and also assures application of the implant to the surface of the bone. Because each facial skeleton has a unique and varying surface topography, a non-conforming implant will leave gaps between the implants and the skeleton. These gaps between the implant and the skeleton are problematic for two reasons. The space between the implant and the skeleton is equivalent to an additional augmentation. This can lead to over-augmentation and asymmetries. Gaps are also potential spaces for hematoma and seroma formation (Fig. 14.5). Finally, screw fixation allows for final contouring with the implant in position. This final contouring is particularly important where the implant interfaces with the skeleton. Any step-off between the implant and the skeleton will be palpable and possibly visible in patients with thin soft tissue cover.

Fig. 14.5 Screw fixation applies the implant to the skeleton and obliterates the gaps which are equivalent to an increase in augmentation. A, Without screw fixation there are gaps between the posterior surface of the implant and the anterior surface of the mandible. B, The screw at the upper border applies the implant to the skeleton. C, The lower screw now obliterates all gaps. The posterior surface of the implant is congruent with the anterior surface of the mandible. The amount of augmentation is equivalent to the thickness of the implant only.

Screw fixation not only prevents implant movement but also obliterates gaps between the implant and the native skeleton. Gaps result in unanticipated increase in implant augmentation.

Midface Implants

Virtually all aesthetic augmentation is performed on the middle and lower thirds of the facial skeleton. The midface is best conceptualized as having three zones, alone, or in combination, appropriate for augmentation. Implants are designed to augment the infraorbital rim, the malar area, and the pyriform aperture.

Infraorbital rim

Because the infraorbital rim and upper midface skeleton support the lower eyelids and the cheek soft tissues, their projection impacts on lid and cheek position. Patients with retrusive skeletons are more likely to undergo premature lower lid and cheek descent with aging. This lack of skeletal support predisposes to lower-lid malposition after blepharoplasty and limits the efficacy and longevity of midface lifting.

Deficient infraorbital rim projection predisposes to lower-lid descent with aging.

Deficient infraorbital rim projection predisposes to lower-lid descent after blepharoplasty.

Jelks and Jelks⁶ categorized globe-orbital rim relationships and the tendency for the development of lower-lid malposition after blepharoplasty. On sagittal view, they placed a line or “vector” between the most anterior projection of the globe and the malar eminence and lid margin. A “positive” vector relationship exists when the most anterior projection of the globe is posterior to the lid margin and the malar eminence. A “negative” vector relationship exists when the most anterior projection of the globe lies anterior to the lower lid and the malar eminence. See Fig. 14.6. They warned that, patients whose orbital morphology has a negative vector relationship are prone to lid malposition after lower blepharoplasty.

Fig. 14.6 Jelks and Jelks^118-6 categorized globe-orbital rim relationships 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.

After Yaremchuk, M.J. Restoring palpebral fissure shape after previous lower blepharoplasty. Plast. Reconst. Surg. 111:441-450.

Augmentation of the infraorbital rim in patients with a retruded infraorbital rim can bring it into a better relationship with the globe, thereby “reversing the negative vector”.⁷ See Fig. 14.6.

Infraorbital rim augmentation is part of the strategy for normalizing the appearance in patients who are “morphologically prone”. It can be adapted for morphologically prone patients who are first seeking improvement in their periorbital appearance or for those whose lid malposition and round-eye appearance that has been exaggerated by previous lower blepharoplasty.⁸

Infraorbital rim augmentation can provide support for the resuspended lower lid and cheek in patients with midface skeletal deficiency.

Surgical technique

The infraorbital rim and adjacent anatomy must be exposed sufficiently to assure ideal implant placement, smooth implant facial skeleton transition, and screw fixation. Direct, subciliary skin or skin muscle-flap incisions can provide this exposure. A transconjunctival incision alone is inadequate for implant placement or screw stabilization. Use of a transconjunctival retroseptal incision requires lengthening with a lateral canthotomy or combination with intraoral and coronal incision. It is important to identify the infraorbital nerve that exits from the infraorbital foramen about 1 cm below the margin of the orbit. This may be 3–6 mm in patients with significant maxillary hypoplasia – usual candidates for this surgery. The orbicularis oculi and the origins of the lip elevators are separated from the underlying skeleton in a subperiosteal plane to expose the infraorbital rim. The implant is carved to fit the specific needs of the patient. Segmenting the implant may facilitate placement of the implant through limited skeletal access. The implant is fixed to the skeleton with titanium screw. This technique is summarized in Fig. 14.7. A clinical example is shown in Fig. 14.8.

Fig. 14.7 Overview of operation to increase projection of infraorbital rim and “reverse the negative vector” in patients with upper midface skeletal deficiency. I prefer a transconjunctival retroseptal incision (broken line) with the lateral extent of a lower-lid blepharoplasty incision (solid line) to expose the infraorbital rim. This approach preserves the integrity of the lateral canthus, and hence, the palpebral fissure. Transcutaneous blepharoplasty or transconjunctival with lateral canthotomy incisions are alternative approaches which provide greater exposure but are accompanied by a greater risk of palpebral fissure distortion. An intraoral incision (broken line) is use to access the lower midface skeleton and to identify and protect the infraorbital nerve. The lower-lid and midface soft tissues are freed by subperiosteal dissection. The implant is immobilized with titanium screws.

Fig. 14.8 Clinical example of a patient who underwent augmentation of the infraorbital rim with an alloplastic implant, subperiosteal midface lift, and lateral canthopexy. A, Pre and postoperative frontal views. B, Pre and postoperative lateral views.

Pyriform aperture

The average North American Caucasian face is convex (Figs 14.4). A relative deficiency in lower midface projection may be congenital or may be acquired, particularly after cleft surgery and trauma. Patients with satisfactory occlusion and lower midface concavity can have their aesthetic desires satisfied with skeletal augmentation. Implantation of alloplastic material in the paranasal area can simulate the visual effect of LeFort I advancement and other skeletal manipulations.⁹

Pyriform aperture augmentation increases the projection of the nasal base and, therefore, opens the nasolabial angle.

Surgical technique

Paranasal augmentation is done through an upper gingivobuccal sulcus incision made just lateral to the piriform aperture to avoid placing incisions directly over the implant. An adequate cuff of mucosa is left to allow layered closure. Subperiosteal dissection exposes the area to be augmented. The infraorbital nerve is identified and preserved. The patient’s anatomy will determine whether the entire crescent or just the horizontal or vertical limb of the crescent will be utilized. The root of the canine usually lies in the field to be augmented and should be avoided if the implant is immobilized with screws. A patient who underwent aesthetic rhinoplasty and augmentation of the pyriform aperture area is shown in Fig. 14.9.

Fig. 14.9 A 20-year-old woman underwent rhinoplasty and pyriform aperture augmentation. Note how augmentation of the pyriform aperture has changed the lower midface shape from concave to convex. A, Pre and postoperative frontal views. B, Pre and postoperative lateral views.

The implant may compromise the nasal airway if malpositioned.

Malar

Prominent malar bones are considered attractive. Hence, the malar area is frequently augmented with implants.

The lack of anthropometric and cephalometric landmarks precludes the availability of normative data making analysis and augmentation of the malar area largely subjective. Malar deficiency is often part of a generalized midface deficiency for which malar augmentation alone may be inadequate or, even, inappropriate. Clinical experience has shown that when malar projection is deemed inadequate, malar augmentation is most effective when it recreates the contours of a normal skeleton with prominent anterior projection. Malar skeletal augmentation is not a substitute for soft tissue augmentation or repositioning.

Since full cheeks are associated with youth, malar augmentation is often performed to provide a youthful appearance. This may provide an aesthetic benefit if there is a relative malar hypoplasia or if the implants are of modest size and projection. This skeletal augmentation is not equivalent to a soft tissue augmentation or resuspension. Similarly, malar implants are often advocated as a means to obliterate lower-eyelid wrinkles or secondary bags. Malar augmentation impacts poorly on these surface irregularities. More often, they detract from periorbital aesthetics by contributing to lower-lid malposition, particularly when placed through an eyelid approach.¹⁰

Skeletal augmentation is not a substitute for soft tissue augmentation or resuspension.

Surgical technique

Malar augmentation can be performed through intraoral, coronal, or eyelid incisions. It is the author’s preference to access the malar midface through an intraoral approach.

An upper buccal sulcus incision is mad e far enough from the apex of the sulcus so that sufficient labial tissue is available on either side for a secure two-layer closure. 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. The pocket size should allow precise insertion of the implant to the area of the skeleton desired for augmentation.

Extending a malar implant onto the zygomatic arch has a profound impact on midfacial width.

Although implants with greater projection are available, I rarely provide more than 3 mm of augmentation at the point of maximum projection. Larger implants will become obvious with time as the overlying soft tissues atrophy and sag. The capsule formation that accompanies smooth-surfaced implants further exaggerates the tendency towards implant visibility.

Large malar implants will become visible with time.

In my experience, implants with large surface areas do not mimic natural skeletal topography and cause unnatural implant-dictated contours. The intraoperative position of both smooth and porous implants can be guaranteed with screw fixation of the implant to the skeleton. See Figs 14.10 and 14.11.

Fig. 14.10 Overview of the operative technique for malar augmentation. The upper buccal sulcus incision is at least 1 cm above the apex so that sufficient tissue is available for closure. Taking care to identify the infraorbital nerve, the subperiosteal dissection is carried over the malar eminence and onto the zygomatic arch just beyond the zygomaticotemporal suture. Implants are fixed with titanium screws. A trochar attached suction drain is placed. It exits through temporal hair bearing scalp. The broken line indicates the buccal sulcus incision. The dotted area denotes the area of subperiosteal dissection. The implant usually extends from the temperozygomatic suture on the zygomatic arch to just below the foramen of the infraorbital nerve. It does not extend beyond the malar bone into the submalar area.

Fig. 14.11 A 24-year-old woman underwent malar augmentation, chin augmentation, and submental lipectomy. A, Pre and postoperative frontal views. B, Pre and postoperative oblique views.

Mandible Implants

Each of the anatomic areas of the mandible – chin, body, angle and ramus – may be deficient and are amenable to augmentation with alloplastic materials. For further information on the chin please see Chapter 13, Genioplasty.

Surgical technique

A generous intraoral mucosal incision is made to expose the ramus and body of the mandible. It 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. If the mental area is also being augmented, a submental incision is made for access and exposure of the anterior mandible. The mental nerve is visualized as it exits its foramen to avoid its injury. It is important to free both the inferior and pos-terior borders of the mandible of soft tissue attachments to allow placement.

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. With vigorous retaction, this is performed intraorally (Fig. 14.12). This allows strategic unicortical screw fixation of the implant to the mandible. Usually two or three screws are used to obliterate any gaps between the mandible and the implant. Screws are placed to avoid the anticipated path of the inferior alveolar nerve prior to its exit from the mental foramen.

Fig. 14.12 Screw fixation of the implant to the mandible through an intraoral approach.

It is crucial to soften any transitions between the implant and the mandible, particularly where the implant extends beyond the anterior mandibular border’s inferior edge. Any step-offs between the implant and the mandible in this area may be visible in thin patients. Screw fixation of the implants allows scalpel or mechanical burr final contouring with the implants in place. A small suction drain may be placed at the operative site that exits through the skin behind the ear. The incision is closed in two layers with absorbable sutures.

Make the intraoral incision at least 1 cm above the sulcus on the labial side to provide adequate soft tissue for two-layer closure and to avoid saliva pooling over the suture line in the early postoperative period.

A clinical example is shown in figure 14.13.

Fig. 14.13 A 30-year-old with mandibular deficiency and orthodontically corrected occlusion underwent chin and mandibular augmentation with alloplastic implants. A, Pre and postoperative frontal views. B, Pre and postoperative lateral views. C, Artist’s rendition of surgery.

Complications

The best available data support the biocompatibility of the currently used implant materials. No cases of cancer have been reported in association with a polymer craniofacial implant. True hypersensitivity reactions to prefabricated polymer implants are extremely rare.

There are no truly scientific data to document the surgical 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. We reviewed almost 200 reports in the literature that provided sufficient data to compare complication rates related both to implant material and implant site.⁴ The accumulation of these clinical data can provide some useful information about factors that can contribute to morbidity with implants. For example, the quality of the soft tissue coverage is clearly related to morbidity. Complication rates are lowest in the chin and malar region, where the soft tissue cover is relatively thick, and highest in the nose and ear, where the soft tissue cover is thin and often under tension from the underlying device. The surface characteristic of an implant may also be important. Porous implants allow a certain ingrowth of tissue which may allow the presence of host defenses within the implant to decrease the risk of infection. Given that several biomaterials are well tolerated in the human body, the actual chemical structure of an implant is important only to the degree that it influences the consistency and surface characteristics of the device.

In 2003, I reported my personal experience with porous implants used for facial skeletal reconstruction.⁸ This report was based on experiences with 162 patients who were operated on over an 11-year period (1990–2001). In this series no implants migrated or were extruded, formed clinically apparent capsules, or caused symptoms attributable to bio-incompatibility. The overall reoperation was 10% (n = 16), which included operations to remove implants because of acute infection (2% – n = 3) or late infection (1% – n = 1), or to remove implants causing displeasing contours (2% – n = 3). The rate of complications has not changed in facial implant procedures in the subsequent 100 patients.

The presence of a foreign body decreases the minimal infecting dose of Staphylococcus aureus in an animal model due to impaired bacterial clearance.¹⁹ If microorganisms are not eliminated rapidly from an implant surface they will adhere to the implant initially by non-specific physical forces and then by the formation of biofilms characterized by clustering together in an extracellular matrix attached to the implant.²⁰ Biofilms protect bacteria from host defenses and antibiotics. Only aggressive debridement and long-term suppressive therapy have been effective in treating orthopedic implant-related infections. This approach is usually not appropriate in facial implant patients since both debridement and chronic infection may be deforming in this appearance conscious population. Since antibiotic treatment alone is usually not successful, facial implant-related infections are treated by implant removal and appropriate wound care. Implants may be replaced in 6 to 12 months.

Conclusion

Augmentation of the facial skeleton with alloplastic materials can be a safe and effective way to alter facial appearance. Virtually any area of the facial skeleton can be augmented. A satisfactory result requires avoiding morbidity in the facial sensory and neuromuscular apparatus during surgical exposure, selecting sites with adequate soft tissue cover and using implants that merge imperceptibly with the adjacent skeleton.