Facial Plast Surg Clin N Am 10 (2002) 325–333

Alloplastic materials for facial skeletal augmentation$

Craig D. Friedman, MD, FACSa,b,*, Peter D. Costantino, MD, FACSc

aFrom Private Practice, Facial Plastic , 4 Greystone Farm Lane, Westport, CT 06880, USA bMedical Research and Development, Biomerix, Inc., 41 West 57th Street, New York, NY 10019, USA cDepartment of Otolaryngology, Roosevelt St. Lukes Hospital, 425 West 59th Street, 10th Floor, New York, NY 10019, USA

Facial skeletal augmentation continues to be an etal augmentations are onlay in nature with the goals important clinical area for surgeons performing cos- of stability and symmetry paramount. Esthetic guide- metic and reconstructive facial surgery. This article lines have been developed and refined to guide reviews the current state of the art approaches utilizing correction of common facial skeletal deficiencies alloplastic materials. Surgical goals, biomaterials, [1]. Additionally, recent attention has been given to operative techniques, and complication management the role of skeletal changes in aging. Both Binder [2] are discussed. Any discussion of alloplastic materials and Pessa et al [3] have shown the value of skeletal ultimately relates tissue effects to long-term clinical augmentation to enhance other aspects of facial results. It may take a full generation (20 years) to rejuvenation, thereby increasing the importance of appreciate fully most if not all possible tissue effects skeletal augmentation in cosmetic facial surgery. of an alloplastic material; however, biomaterial sci- Inlay applications for skeletal defects (of a trau- ence has developed fundamental principles that matic or oncologic etiology) additionally require vol- should aide the surgeon in choosing the most appro- ume maintenance over time to preclude defect priate alloplast for skeletal augmentation for various reformation. Volume maintenance over time is a key patient groups. advantage of commonly used alloplastic implants. In the past the goal of stable volume was believed to be due to utilization of an inert implant material and minimal tissue response over time. This view of Surgical goals implants has been found to be naive with respect to tissue–implant interface biology. Improved under- Clinical judgment always remains the most standing of interface biology has revealed the limi- important arbiter in selecting the appropriate implant tations of many implants and helped encourage the and surgical approach for an individual patient. development of bioactive implants [4]. Bioactive Patient implant requirements can be routinely clas- implants are biomaterials that allow for biologic sified as either onlay or inlay with regards to the type bonding of tissue to implant, which permits natural of skeletal augmentation. Purely cosmetic facial skel- tissue regeneration as opposed to chronic foreign body or inflammatory reaction. Bioactive interfaces theoretically reduce micro- motion and implant mobility over time. Secure $ This article is reprinted in an abridged format from: implant fixation allows for less opportunity of motion Friedman CD, Constantino PD, Sajjandian A. Alloplastic materials for facial skeletal augmentation. Facial Plast Surg at the interface to induce wound inflammation. Clin N Am 1999; 7(1):95–103. Chronic inflammation over the long term leads to * Corresponding author.. formation of avascular fibrous capsules. Although E-mail address: [email protected] such tissue reaction may by clinically quiesent, it (C.D. Friedman). can lead to gross implant mobility and secondary soft

1064-7406/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S1064-7406(02)00022-6 326 C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 tissue changes in the long term. Therefore, stable and acterized by various amount of fibrous and fibrovas- secure implant fixation becomes a very important cular ingrowth. Although polyethylene can support clinical goal that affects outcome. surface conduction of viable osteocytes, true inte- grative osteoconduction throughout an implant has not been documented by experimental results [8,9]. Implant materials Fibrovascular ingrowth makes porous polyethyl- ene an attractive implant for facial skeletal augmen- There are four commonly used implant materials tation for the following reasons. First, the ingrowth for facial skeletal augmentation: (1) silicone elasto- stabilizes fixation of the implant. Second, the implant mer, (2) porous polyethylene, (3) expanded polytetra- may be resistant to infection and therefore potentially fluoroethylene (ePTFE), and (4) hydroxyapatite– salvaged in the face of exposure if sufficient vas- calcium phosphate. Detailed implantology informa- cularity is present [10]. Fixation of implants is most tion on these materials can be found elsewhere in this commonly achieved with metal screws. issue. The tissue–implant interfaces exhibited by these materials are important to understand so that Expanded polytetrafluoroethylene clinical effectiveness is maximized. Expanded polytetrafluoroethylene (Gore-Tex, WL Silicone Gore, Flagstaff, AZ) has been used extensively as a soft tissue implant and vascular prosthesis. Various Silicone elastomer is a solid rubber–consistency formulations of fibrils are combined to create polymer of polymethyl siloxane. Due to its relative implants with pores of up to 30 lm. The tissue– inertness as an implant it has been developed for implant interface is usually that of limited fibrous many medical applications and specifically facial tissue ingrowth without significant capsule formation. skeletal augmentation [5]. Preformed shapes for Interesting recent experimental data have revealed nasal, malar, and augmentation have been in differential healing responses to ePTFE dependent use for many years. The tissue–implant interface is upon the anatomic site of implantation [11]. Such one of an avascular fibrous capsule. Capsular con- experiments shed light on potential uses in facial traction aides in securing the implant to a fixed implantation and the important questions that remain position over time. Initial fixation of silicone implants unanswered. Preformed chin and malar implants are should be attempted. Many surgeons prefer place- available, but the most common use is to augment the ment in a defined supraperiosteal pocket; others have nasal dorsum in reconstructive surgery. Extensive modified this by use of nonresorbable sutures or experience in this use has been reported with favor- metal screws. able outcomes [12]. Gore-Tex nasal augmentation The most commonly associated unfavorable result ultimately requires comparison with autogenous tis- with silicone implants has been underlying bone sue to make the final assessment of outcomes. resorption. This was identified by Robinson and Shuken [6] in 1969 and has been recounted in many Hydroxyapatite reports subsequently. Matarasso et al [7] have recently summarized these reports and provide findings that Currently, many forms of calcium phosphate and call for caution in advocating silicone chin implants hydroxyapatite biomaterials exist and have extensive for certain patient groups. Despite this well-known use in facial skeletal augmentation. These materials information, silicone implants remain popular and should be classified as bioactive in nature. The readily accepted by surgeons and patients. tissue–implant interface can be categorized as show- ing osteoconduction and osseointegration over time. Polyethylene Interested readers should consult previous reviews for comprehensive details on synthetic bone substitutes High-density porous polyethylene (MedPore, [13]. This discussion only highlights those materials Porex Industries, Fairburn, GA) has gained consid- in general use and emphasizes new information erable acceptance as an implant for facial skeletal relevant to clinical issues. augmentation. It is a particulate high-density polymer Hydroxyapatite biomaterials can be broadly cate- of ethylene that is then fused by a sintering process gorized into ceramic and nonceramic classes. Ceramic into a porous solid material. Pore size ranges from material of a porous nature has been used as an onlay 100 to 300 lm. The material is somewhat flexible and material for facial skeletal augmentation [14]. This readily carved. The tissue–implant interface is char- porous hard material (Interpore, Irvine, CA) has pore C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 327 sizes of up to 300 to 500 lm, which allows for fibro- surgery, to concealed incision surgery, and now mini- osseous conduction at the interface. The main clinical mally invasive endoscopically assisted approaches difficulties have been contouring the edges of the (Louis Morales, personal communication, 1997). Most implant for blending purposes and initial fixation with of the fronto-orbital and midfacial skeleton can be screws, which can lead to problematic implant frac- exposed via coronal scalp incisions and flap elevation. tures. Other surgeons have used granules of porous The midfacial and mandibular skeleton is most often hydroxyapatite for facial augmentation by limiting exposed via intraoral approaches. The nasal region is dissection and exposure to subperiosteal pockets for easily accessed with endonasal incisions. Fig. 1 illus- implant placement and awaiting initial soft tissue trates the authors’ preferred technique for the place- ingrowth healing to stabilize the implant [15]. ment of a chin implant. The intraoral dissection allows Hydroxyapatite cement (BoneSource HAC, Lei- for better visualization, which aids placement and thus binger, Dallas, TX) is a nonceramic cement formula- avoids malposition asymmetries. Use of metal screws tion recently cleared for clinical use in facial skeletal provides both initial and long-term fixation. Compared augmentation [16–19]. The key characteristics of the with transcutaneous submental approaches, attention cement are a true setting material that starts as a to reattachment of the mentalis muscle is important in powder and after mixing with a liquid phase becomes avoiding postsurgical lower incompetence. a paste or putty consistency. While in the paste state the With any approach, selection of the final tissue material can be shaped to the desired contour and plane for implantation is important. For the com- dimensions. It then sets to a hard consistency. Bone- monly used materials (discussed previously), con- Source has a microporous structure with pore size sensus opinions can vary with individual surgeon’s approximately 3 to 9 lm. Once set the material has a preference. Silicone polymer is most often recom- compressive strength in the range of 60 to 70 mPa. mended to be placed in a supraperiosteal plane so Like most inorganic materials, it has limited shear as to encourage fibrous capsule formation, which resistance and therefore should not be used in areas of hopefully stabilizes the implant position. Bone significant torsional loading without additional sup- resorption has been noted with implants placed in portive hardware. The tissue–implant interface is the subperiosteal plane, and therefore for the chin characterized by osteoconduction and osseointegra- area especially supraperiosteal placement is advo- tion. Over time the implant is converted to bone. The cated. For Gore-Tex, a supraperiosteal placement is conversion to bone occurs in a progressive fashion reasonable; however, subperiosteal placement has maintaining volume. It is more rapid in void defects not been reported as advantageous or contraindi- and younger animals. When placed in an onlay posi- cated. For porous polyethlyene and hydroxyapatite tion with viable periosteum, BoneSource develops a implants, placement in a subperiosteal plane is thin overlying surface of bone and a replacement recommended and advantageous from a tissue– surface at the bone–implant interface. BoneSource interface perspective. has excellent adhesion to bone surfaces, and therefore Fixation of implant material affords the best additional fixation devices are not routinely used. opportunity to diminish or preclude micromotion and the development of chronic inflammation. Inflammation from motion can facilitate secondary Technical considerations for implantation bacterial seeding, particularly when the surgical approach is introral or the implant has physical Surgical technique affects both short-term and proximity to dental structures. Sometimes this goal long-term outcomes in facial skeletal augmentation. is impractical given the surgical location or exposure. General principles of surgical implantation are well Traditionally, limited dissection pockets were advo- established, such as avoidance of contaminated fields, cated when the implant was placed. Surgical tech- use of perioperative antibiotics, and meticulous intra- nique has sequentially advocated suture fixation and operative handling of the implant materials. Careful then metal screw and plate fixation. The caveat that preoperative assessment of the recipient site should should be remembered is that any fixation is better determine whether adequate vascularity and soft than none. In the nasal area suture fixation, particu- tissue coverage are present. If not, then consideration larly of Gore-Tex, is easiest. Titanium microscrew should be given to staged procedures with inset of systems are now the standard fixation choice with vascularized tissues and soft tissue augmentation preformed implants. prior to skeletal augmentation. BoneSource HAC does not require adjunctive Surgical approaches to the various sites of the facial fixation due to its bone adherence qualities; however, skeleton have evolved from a direct transcutaneous the use of cement does require a higher level of 328 C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 technical attention when used for cosmetic skeletal desired maximum projection and then apply the augmentation. This requirement is due to the actual BoneSource HACement to envelop the screw with qualities of a cement material; in order to ensure esthetic tapering of the peripheral implant. This symmetric skeletal augmention it is recommended technique is illustrated in Fig. 2 for the malar ana- that a titanium microscrew be placed at the point of tomic site. The advantages of BoneSource HACe-

Fig. 1. Technique for alloplastic chin augmentation. (A) General anterior view with desired positioning of the implant. (B) Lateral view with superimposed Gonzales-Ulloa projection line. Note the idealized soft tissue profile. (C) Proposed incision in the labio- mental sulcus. (D) Surgical exposure of the mandibular mentum area. Note preservation of the mental nerves and mentalis muscle attachments. (E) Fixation of implant with screw. Note marking of midline to assure central placement and symmetry. ( F) Surgical closure of the wound in layers, attention to reattachment of the mentalis muscle to prevent postoperative lip incompetence. C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 329

Fig. 1 (continued). ment are that it affords custom implant fabrication (in reports on facial implant materials. Although certain situ) and a bioactive interface that results in osseoin- trends can be appreciated, it must be recognized that tegration, and thus represents the current state of the most patients with unfavorable results with facial art for facial skeletal augmentation. skeletal augmentation implants rarely return to the original surgeon. Therefore, literature reports are unable to provide data of sufficient quality to make Unfavorable results and complications definitive statements on implant performance over time. Beyond immediate common surgical complica- When patients undergo surgery, the expectation is tions (ie, bleeding and hematoma), the following that an uneventful surgery will result in attainment of areas of concern need to be addressed: mobility or preoperative goals. The reality is that all surgical malposition, infection, exposure, soft tissue changes, procedures have associated unfavorable results and and unwanted esthetic results. complications. Facial skeletal augmentation is not Mobility and malposition are complications that immune from unfavorable results; however, these appear to be infrequent and with the use of stable outcomes appear to be infrequent and make such fixation preventable. The most common implant to procedures very successful. A recent review by Rubin exhibit mobility has been silicone polymer. When one and Yaremchuk [20] summarizes conveniently many considers the nature of the tissue–implant interface, it 330 C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333

Fig. 2. Surgical technique of alloplastic midfacial augmentation with BoneSource-Hydroxyapatite (Leibirzen, Inc., Dallas, TX) cement. (A) Lateral profile of midfacial hypoplasia. Note lack of malar eminence projection. (B) Anterior view of midfacial hypoplasia. Note elongated appearance of the midface. (C) View of malar eminence where augmentation is required. (D) Surgical exposure of the malar eminence and through gingival-buccal/labial inc. Note careful identification and preservation of the infraorbital nerve. (E) Placement of titanium microscrew in the malar eminence, and use of calipers to determine the exact amount of desired projection. ( F) Placement of BoneSource-Hydroxyapatite cement by spatulation of the setting paste. ( G) Closure of the wound in layers. Note the screw is totally embedded in cement. C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 331

Fig. 2 (continued). is readily appreciated as to why this occurs. Implants dental structures) near facial implants imparts an that exhibit tissue ingrowth are less likely to become increased risk. Traditional surgical principles tell us mobile, whereas implants such as hydroxyapatite, that clean-contaminated have an inherent which have bioactive tissue interfaces, are ideal. infection rate of approximately 1% to no more than Patients with mobile implants should be evaluated 1.5%; facial skeletal alloplastic implants necessarily for chronic low-grade infection versus inflammation have a somewhat greater incidence of infection related to the underlying implant mobility. If chronic requiring implant removal. Thus, reported rates of infection becomes manifest, then implant removal is infection have ranged up to 12%, with most studies recommended. Immediate replacement should only somewhere between 3% to 7%. Those studies that be entertained in those instances of inadequate report infection rates of less than 1% usually have implant fixation and not infection. serious methodology issues and should be carefully Infection related to biomaterial implants is for the scrutinized. As previously noted, the nature of the most part localized to the area of implantation. The tissue–implant interface dictates success in managing anatomic location of colonized areas (nasal, oral, and infection with antibiotics. In particular, implants such 332 C.D. Friedman et al. / Facial Plast Surg Clin N Am 10 (2002) 325–333 as MedPore may be salvaged if significant fibrovas- Summary cular ingrowth has occurred. Patients with implants should have prophylaxis for procedures that can Alloplastic implants are commonly used for facial induce transient bacteremia. If infections cannot be skeletal augmentation with good success. Under- eliminated with appropiate antibiotic therapy, then standing the tissue–implant interface is important removal is necessary. for the successful clinical application. Current Exposure of implants presents a difficult clinical implant technology is focusing on bioactive implants management dilemma. Dependent upon the location that modulate normal wound healing to promote a and nature of the implant material, exposure can be natural tissue–implant interface and, it is hoped, managed with several strategies. If the exposure is better long-term functional outcomes. limited and thought to be related to wound margin issues, such as tension or inadequate blood supply, then careful reclosure can be attempted. If the expo- References sure is limited and thought to be related to infection, then local wound care and hygiene along with anti- [1] Epker BN. Esthetic maxillofacial surgery. Malvern biotics can be attempted. 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