Distraction Osteogenesis of the Craniofacial

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CME

Distraction Osteogenesis of the CraniofacialSkeletonJack C. Yu, M.D., D.M.D., Jeffrey Fearon, M.D., Robert J. Havlik, M.D., Steve R. Buchman, M.D., andJohn W. Polley, M.D.

Augusta, Ga.; Dallas, Texas; Indianapolis, Ind.; Ann Arbor, Mich.; and Chicago, Ill.

Learning Objectives: After studying this article, the participant should be able to: 1. Review the biomechanical principlesand pertinent cellular and molecular biology of distraction osteogenesis of the craniofacial skeleton. 2. Describe the

clinical indications and applications of distraction osteogenesis of the craniofacial skeleton. 3. Describe maxillary,mandibular, midface, and calvarial procedures in distraction osteogenesis. 4. Discuss the clinical outcomes and compli-cations of distraction osteogenesis of the craniofacial skeleton.

The year 2002 marked the end of the first decade inclinical distraction osteogenesis of the craniofacial skele-ton. In this short period, its application has increasedexponentially. More than 3000 cases have been performedaccording to a recent survey, and more than 700 articleshave been written on this subject in the MEDLINE data-base since 1996. It is a powerful surgical tool and enablessurgeons to achieve results not previously attainable. De-spite all this, distraction osteogenesis is practiced by onlya small number of plastic surgeons. This article reviews thebiomechanical principles; the pertinent cellular and mo-lecular biology; and the clinical indications, applications,controversies, and complications of distraction osteogen-esis of the craniofacial skeleton. (Plast. Reconstr. Surg.114: 1e, 2004.)

Plastic surgeons alter the product of mor-phogenesis. The natural attainment of bodyform is a multifactorial, polygenic process. Akey ingredient of this complex process is me-chanical force. Force is completely ubiquitous;it can originate from local growth, the earths

gravitation, muscular contraction, and surfacetension, to name just a few sources. Cellularresponse to force is therefore a very ancientand critical part of the biotic process.1,2 Distrac-tion osteogenesis, like soft-tissue expansion,taps into this ancient, universal property: growif stretched. Initially used in orthopedic sur-gery by Codivilla in 1905,3 it was systematically

developed and refined by Ilizarov.4,5 Ilizarovsmeticulous work definitively established thefact that bone will form in response to tension.This apparently contradicted Wolffs law re-garding bone remodeling, which associatesbone formation with compression and boneresorption with tension.6 In 1992, McCarthy etal.7 reported in the English literature the firstapplication of distraction osteogenesis tolengthen the human mandible. This method isnow used extensively at every level of thecraniofacial skeleton.813 There are three mainphases to distraction osteogenesis: latency, ac-tivation, and consolidation. Latency is that pe-riod immediately following the osteotomy andapplication of distractor; it ranges from 1 to 7days. After the latency phase is the activationphase. During this phase, the distraction deviceis activated by turning some type of axial screw,usually at 1 mm/day in four equal incrementsof 0.25 mm each. Once activation is complete,the third and final phase is the consolidationphase. Typically, the consolidation phase istwice as long as the time required for activa-tion. The above three phases constitute theIlizarov protocol designed for lengthening thelong, endochondral bones of the lower extrem-ity. Whether this is the optimal protocol for the

From the Section of Plastic Surgery and Craniofacial Center,Medical College of Georgia; theCraniofacial Center,Medical City Dallas Hospital;Riley Hospital for Children, Indiana University School of Medicine, Section of Plastic Surgery; Craniofacial Anomalies Program, C. S. MottChildrens Hospital, Section of Plastic Surgery, University of Michigan; and Department of Plastic and Reconstructive Surgery and RushCraniofacial Center, Rush-Presbyterian-St. Lukes Medical Center. Received for publication January 26, 2004; revised March 12, 2004.

DOI: 10.1097/01.PRS.0000128965.52013.95

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craniofacial skeleton as well is not completelyclear.14,15 Today, many different devices are be-ing used clinically, with many different distrac-tion protocols.16

This review article describes the biomechani-cal, cellular, and biomolecular events that oc-

cur during distraction osteogenesis. The indi-cations, clinical applications, controversies,outcomes, and potential complications of dis-traction osteogenesis in the craniofacial skele-ton are discussed at each level, from the man-dible to the forehead.

BIOMECHANICS OF DISTRACTION OSTEOGENESIS

Distraction osteogenesis can be consideredas a very special, altered form of fracture heal-ing.17 It represents an effective and long-termaugmentation of the human morphology by

using mechanical force to induce and directbone and soft-tissue formation.18 Unlike expan-sion of the soft tissue by tissue expanders, theosseous tissue, once produced, does not con-tract over time after the removal of the ex-pander device. This is because bone is rigid,and it responds to the mechanical demandsplaced on it.19 Bone is the only living tissue thatcan effectively withstand both tensile and com-pressive loads, with a tensile strength of 12,000psi and a compressive strength of 15,000 psi.20

To achieve targeted bone growth, a rigid

stretching device delivers tensile force to thedeveloping callus at the site of the bone cut(periosteum- and marrow-sparing corticoto-mies in the original Ilizarov protocol; completeosteotomies in most craniofacial centers now),a process known as callotasis. In response tothis force, the callus elongates.21 The amountof elongation as a fraction of the originallength is known as tensile strain. In distractionosteogenesis, the typical protocol is 0.25 mm atfour times per day, or 1.0 mm/day. In mostcases, the osteotomy creates an initial defect ofapproximately 1.0 mm. Thus, the strain is 100percent during day 1 of activation and drops to50 percent for day 2 and 33 percent for day 3.By day 10, the theoretical strain induced by 1.0mm of elongation in a 10-mm callus is de-creased to 10 percent. This reduction in strainas distraction progresses is inevitable given aconstant distraction rate.22 Bone tissue as a ma-terial can tolerate only 1 to 2 percent of tensilestrain, a parameter known as ultimate tensilestrain. Thus, no bone tissue can exist if the loadenvironment produces more than 1 to 2 per-cent tensile strain. In normal fracture healing,

ossification is seen when the interfragmentarystrain is below the ultimate strain. Not surpris-ingly, by week 4 of distraction, with the tensilestrain approaching or below the ultimate strainlevel, bone formation starts.23 On microscopy,the classic description is that there are five

histologic zones: one central zone of fibrosisbordered on either side by the two transitionalzones, which are themselves bordered by theremodeling zones. The central zone is betterdescribed as the central zone of mesenchymalproliferation.24 The current concept also hasfive zones but adds four transitional areas be-tween the zones. It assigns two paracentralzones, one on each side of the central zone,joined by the transitional area of vasculogen-esis. Peripherally, the paracentral zones borderthe proximal-distal zone, separated from them

by another transition area: the area of miner-alizing fronts where the highest ratio of celldivision was observed throughout the activa-tion phase (Fig. 1). Apoptosis is present in theparacentral zones. Woven bone is the first typeof bone to appear. It is not clear at presentwhich of the five zones or four transitionalareas are actually structurally the most likely toundergo tensile strain in response to the ten-sile stress imparted by the distractor. This willdepend on the elastic modulus of the variouszones and transitional areas, which has not yet

been measured or reported. Very limited di-rect biomechanical characterization is avail-able even from animal experiments. Mofid etal.25 reported recently that, using a standarddistraction protocol in New Zealand White rab-bits, the mandibular regenerate after 8 weeksof consolidation had a bending stiffness of 200N/mm, which was approximately 50 percent ofthe intact mandible. The test was three-pointbending and the load rate was 0.1 mm/second.Robinson et al.26 reported that the averagetorque required to distract human mandiblesat 0.5 mm/day was 4.2 1.6 Ncm, whichcould be converted to an estimated linear ten-sile force of 35.6 N. The distractor for thatstudy had a failure, or yield, force of 235.8 N.

All distractors have the following three com-ponents: an intraosseous component, to trans-mit the displacement to bone/callus; an an-chorage component, to push or pull against;and some type of axial screw which, whenturned, generates the primary displacement.The system is configured in such a way that it isonly as strong as the weakest link: any singlecomponent failure will result in the failure of

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the distraction process. There are two majortypes of distractors: internal and external. Aninherent difference in force delivery betweenthe internal and external distractors is the dis-tance from the callus surface to the activatingaxial screw. The closer this activating axialscrew is to the central (neutral) axis of thebone/callus, the more effective the stretching.

This is because whenever the force vector is notdirectly coaxial, or in line, with the central axisthere will be a turning moment. The externaldevices rely on intraosseous pins to transmitthe force. The longer the distance from theaxial screw of the distractor to the callus, theless effective the distraction. Internal distrac-tors thus enjoy reduced perpendicular distancefrom the callus to the activating axial screw.However, this advantage comes at increaseddifficulty at the time of device removal that canadd significantly to the overall morbidity. Theexternal distractors allow for easier adjustmentof the direction of the distraction. Of the twoprincipal means of delivering the tensile forcein achieving distractionpush or pullinternal distractors are limited to only pushingapart the bone segments. The external distrac-tor with half-halotype anchorage achieves dis-traction by pulling. The actual magnitude offorce required to elongate the callus is un-known and is likely to vary from site to site andfrom individual to individual. Polley andFigueroa27 reported using a 10-N force bymeans of heavy elastics to gradually distract the

maxilla. Using torque wrench measurements,turning moments from 14 to 18 Ncm weredelivered to the activating screw of the distrac-tor in one center.28 Because it is difficult topredict precisely what the total resistance is,the planned distraction trajectory may differfrom the actual trajectory obtained during dis-traction. This has been confirmed in simulated

internal mandibular distraction with and with-out soft tissues such as masseter, temporalis,and the suprahyoid muscles.29

CELLULAR AND MOLECULAR BIOLOGY OFDISTRACTION OSTEOGENESIS

Bone is a highly specialized connective tis-sue. It differs from all other nonmineralized,connective tissue in that it is hard (Vickershardness of 30 kg/mm2 for young humanbones and 38 kg/mm2 for mature humanbones when measured wet).20 This hardness isattributable to the mineralization of the fibril-lar extracellular matrices. There are many re-ports based on animal models of the cellularand molecular events that occur during thedistraction of a healing bone callus.30 32 Forobvious reasons, there are no comprehensivecomparable human data. Immediately afterthe osteotomy, the formation of hematomaand inflammatory infiltrates is exactly the sameas in any standard osteotomy or low-energyfracture. There is a decrease in oxygen tensionand local pH and a reversal of the electric fieldpotential, with the fractured bone ends attain-

FIG. 1. A diagram of the five zones and four transition areas of the distraction gap during the middle,activation phase. The five zones are the central zone (C), the paracentral zones (PC), and the two proximal/distal zones (PD). The four transitional areas are the two areas of vasculogenesis ( v) and the two areas of

mineralization fronts (mf). The central zone is the most cellular and most blastema-like. The transitional areaof mineralization front shows clear anisotropy, with the nascent trabeculae in perfect alignment with the lineof tensile force.

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ing a more positive charge, approximately 1mV, whereas the fracture hematoma demon-strates a sharp increase in electronegativity to6 mV.33 Toward the end of the latency pe-riod, by day 5 after osteotomy, the site is filledwith granulation tissue packed with round,

cuboidal mesenchymal cells and nascent capil-laries. The orientations of the cells, capillaries,and matrices at this time are isotropic (randomorientation). There is a rapid decrease in thelevel of mRNA of bone-specific proteins andextracellular matrices such as osteocalcin andtype I collagen, respectively. This is not surpris-ing, because the tissue being assayed by North-ern blotting is not really bone but rathergranulation tissue. Of note was the rapid in-crease of the transforming growth factor-1mRNA level to 2.5-fold of the normal bone by

day 3 of the latency period.34

As distractionprogresses, the differences between fracturehealing and distraction become more obvious.Mechanical strain is a critical factor. Ilizarovasserted that the alteration of the mechanicalenvironment within the distraction gap led tostimulation of both proliferative and biosyn-thetic cellular functions.4 More recent re-search has focused on precisely what theseevents are.35,36 There is increased cell divisionwith the proliferation index, as measured byproliferating cell nuclear antigen immunohis-

tochemistry, being highest at the mineraliza-tion fronts. The cell types begin to appearmore fusiform in shape. The more centralarea, however, retains the more cuboidal,primitive mesenchymal appearance. As distrac-tion progresses, the most striking feature is thetremendous degree of anisotropy at the junc-tion of the osteotomy site and mineralizationfront; the orientation is now parallel to the lineof tension. In the region immediately adjacentto the central zone, there are many apoptoticfigures. Here, in the paracentral zones, thecellularity decreases and ground substances ac-cumulate. Between the central zone and theparacentral zone is the transitional area, wheremuch vasculogenesis occurs. The mRNA pro-file at this early to mid-activation phase is arapid and sustained increase of the transform-ing growth factor-1 mRNA level, with a slowbut steady increase in the mRNA of type Icollagen. Lagging behind is the bone-specificosteocalcin mRNA. At the end of the activationperiod, there is clear anisotropy, with the bonetrabeculae in perfect alignment with the direc-tion of the distraction.

Not all distractions require an osteotomyfirst. In the distraction of the immature cra-nium, sutures may serve as the callus.37,38 Dis-traction of the cranial sutures has been shownto reduce the level of some key signaling pep-tides that are very important during embryo-

genesis and development. The three proteinsof the hedgehog family, Shh (Sonic hedge-hog), Ihh (Indian hedgehog), and Dhh(Desert hedgehog), are such examples. Thesesignaling proteins bind to a class of transmem-brane receptors, patched-1, and alter the activ-ity of protein kinase A, which sets off a cascadeof intracellular molecular events. Tensile stressproduced by the distraction appears to reducethe level of the hedgehog proteins and theirreceptor, patched-1, in all regions of theperisutural tissue, especially the periosteum.

Of particular interest is the observation thatsuch reduction renders a synostosing suturemore like a normal one.39 However, how theapplied tensile force actually causes the ob-served alteration in cellular and molecular ac-tivities is obscure.

To understand how distraction forces regu-late the creation and differentiation of newbone, it is critical for an experimental model todistinguish new bone formation attributable todistraction from secondary bone formation re-sulting from unaided fracture healing. A rat

model of distraction osteogenesis that does dif-ferentiate between those two fundamentalmechanisms of new bone formation has beenestablished.40 The model documented a criticaldefect size in the rat mandible for discrimina-tion of new bone formation attributable to dis-traction from unaided fracture healing at thesite of the osteotomy. The distraction protocolwas then performed with a defect larger thanthat critical size. Determination of a critical-size defect allowed clear identification of newbone formation attributable to distraction pro-cesses alone. The model also included analysisof a subcritical-size defect that uniformly healswithout difficulty, allowing a comparison ofnormal fracture healing at the same anatomi-cal site, in the same animal model. This modelhas permitted isolation of the variables neces-sary for identification of the significant differ-ences between distraction osteogenesis and os-teotomy alone and to more accurately attributethe changes to the specific stimuli producedby the process of distraction. It has been hy-pothesized that mechanical forces created dur-ing distraction osteogenesis are responsible



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for the osteogenic responses, and that thesechanges arise through integrin-dependentmechanotransduction. Mechanotransductionis the process by which mechanical forces areconverted to cellular signals. These forces ex-ert their effects by means of many pathways.1,2

One such pathway is integrin-dependent signaltransduction.41 The integrin-mediated signaltransduction cascade has been proposed as aprimary pathway by which mechanotransduc-tion occurs.42 46 Many in vitro experimentalstudies focusing on cells subjected to mechan-ical loading have investigated signal transduc-tion during bone growth and adaptation.Within the integrin-mediated signal transduc-tion cascade, focal adhesion kinase, c-Src(pp60c-src) and mitogen-activated protein ki-nase are believed to be key molecular media-

tors.47

Although these mediators have beenstudied extensively in vitro, insufficient re-search had been completed to date evaluatingtheir role and the molecular mechanisms ofintegrin-mediated mechanotransduction invivo. Using the rat model of distraction osteo-genesis, the expression of focal adhesion ki-nase, c-Src, and mitogen-activated protein ki-nase in critical-size and subcritical-size defectswas examined. Findings demonstrated immu-nolocalization of all three molecular mediatorsin mandibles undergoing distraction osteogen-

esis but not in the critical-size or subcritical-sizedefects, despite varying degrees of bone forma-tion in the latter two groups.48 50 Furthermore,the mRNA in situ hybridization patterns ofbone-specific proteins, such as bone sialopro-tein, were found to mirror focal adhesion ki-nase immunolocalization patterns in mandi-bles undergoing distraction osteogenesis,demonstrating an association of focal adhesionkinase expression with the osteogenic processspecific to distraction osteogenesis. These find-ings support the belief that bone formation indistraction osteogenesis is regulated by me-chanical forces and these forces act at the cel-lular and molecular level by means of integrin-mediated signal transduction pathways.Investigation of the cellular and molecular bi-ology of distraction osteogenesis is still in itsinfancy, but new discoveries show promise tosignificantly increase our understanding of theintricacies of this fascinating process.

MANDIBULAR DISTRACTION OSTEOGENESIS

The mandible was the initial site of applica-tion of distraction osteogenesis in the face. The

mandibles structure is similar to the tubularstructure of the long bones of the skeleton.Principles learned by orthopedic surgeons overthe previous 80 years from distraction of thelong bones of the lower extremity were rapidlyadapted to this new location.51,52 Distraction

osteogenesis has provided a powerful tool fortreatment of many mandibular deformitiesthat previously could not be successfullytreated by the conventional methods of or-thognathic surgery, free tissue transfer, or non-vascularized bone grafts.53 In addition, the useof distraction osteogenesis has been extendedinto applications that have been previouslytreated by one of these other conventional ap-proaches to optimize outcome.54

The two major strengths of distraction osteo-genesis in mandibular reconstruction are the

ability to provide strong bone with an excellentblood supply and the ability to provide effec-tive expansion of the soft-tissue envelope.55,56

The importance of expansion of the soft-tissueenvelope cannot be stated strongly enough,because the gradual expansion of the soft tis-sue over an extended period of time is muchmore effective than that which can be obtainedin the short time window of a single operation.These two factors together allow a muchgreater skeletal advancement than can be ob-tained using conventional techniques and al-

low the creation of a construct that is stable inthe advanced and reconstructed position. Thisis in contrast to the considerable relapse thatcan often be seen after conventional proce-dures in larger-scale advancements.

One of the primary planning considerationsin mandibular distraction osteogenesis is theuse of either an external distraction frameworkor an internal device. Critical to this decision isan evaluation of the goals of the distractionprocess.57 The external devices have the pow-erful advantages of allowing bone distractionin three planes and allowing the surgeon toalter the direction, or vector, of the distractionprocess while the distraction is proceeding.Pensler et al.58 first reported this principle ofmolding the regenerate. The moldingtakes advantage of the ability to manipulate thesemisolid state of the nonmineralized, andhence nonrigid, bone in the distraction gap.This allows for fine-tuning of the distractionprocess while the distraction is proceeding,and thus permits dental relationships to beadjusted before the patient enters the consoli-dation phase of bone healing.59 The external



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framework also allows greater amounts of ulti-mate expansion length. Expansions of 40 mmor greater have been reliably obtained. Thedisadvantages of an external frame distractorare the creation of a facial scar and the in-creased distance from the body of the distrac-tor to the bone surface, leading to a longermoment arm at the pin-bone interface andan increased possibility of pin loosening. Inaddition, there is the need for pin care by thepatient at the percutaneous pin sites.60

The child in Figure 2 has several congenitalproblems, including VATER association (verte-bral defects, anal atresia, tracheoesophagealfistula with esophageal atresia, and radial andrenal anomalies) and a severely hypoplasticmandible. She required tracheostomy duringinfancy, and she remained tracheostomy-dependent at 9 years of age. An external mul-tiaxial distraction technique was selected be-cause of the need to provide for stable fixation

in the severely hypoplastic mandible and lim-ited jaw opening and small mouth that pre-cluded consideration of an internal device. Af-ter distraction of approximately 38 mm, thechilds tracheostomy was successfully decannu-lated. Her preoperative and postoperative pho-

tographs are shown. Her advancement hasbeen stable, without relapse, for the past 5years.

An internal distraction framework may beused if the goal of distraction is to provide amoderate gain in length in only one direction.The osteotomy is made transorally, and thedistraction frameworks are placed using atransbuccal percutaneous technique. The goalof distraction with internal devices is generallymore modest, in the range of 25 mm or less.This is a consequence of the constraints placed

on the physical size of the device and the abilityto fit it within the mouth. In addition, thedirection of the distraction cannot be alteredafter the device is placed. This inability to alterthe vector of distraction dictates that unless thedistraction frameworks are placed with a per-fect vector of distraction initially, larger-scaledistractions will lead to larger and larger dis-crepancies as the axial length of the distractionvector proceeds. The child in Figure 3 hasMoebius syndrome, cleft palate, and a severelyhypoplastic mandible. She had a tracheostomy

placed shortly after birth and remained trache-ostomy-dependent at 3 years of age. Preopera-tive planning revealed the need for single-vector sagittal advancement of the mandible.Bilateral mandibular osteotomy and placementof internal framework bone distraction deviceswere performed using a percutaneous tech-nique. The child underwent bilateral distrac-tion of 25 mm on each side, with a linearadvancement of the mandible. Note that theadvancement has led to an improvement infacial and dental relationships and minimalscarring. The technical considerations in thistype of procedure are significant. After osteot-omy and greenstick fracture of the mandib-ular bone, the surgeon is essentially trying tocontrol three separate components (fixator,proximal, and distal bone segments) simulta-neously through the mouth and percutane-ously through the cheek. This is compoundedby the fact that in these congenital cases, themandibular segments are often small, andthere is the need to obtain favorable alignmentto allow the establishment of an appropriatevector of distraction. When the operation is

FIG. 2. A child with VATER syndrome (vertebral defects,anal atresia, tracheoesophageal fistula with esophageal atre-sia, and radial and renal anomalies) and severe mandibularhypoplasia requiring tracheostomy during infancy. Multipla-nar distraction lengthened the mandibular corpus by 38 mmand allowed successful decannulation. (Above, left) Early into

the activation phase. (Above, right) Toward the end of theconsolidation. (Below, left) Preoperative lateral view. (Below,right) Postoperative lateral view.



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completed with appropriate rigid bone fixa-

tion, the results of distraction osteogenesis canbe quite dramatic.In addition to the decision regarding inter-

nal or external distraction frameworks, othercrucial parameters are the selection of osteot-omy site and pin site and the consideration ofthe location of the inferior alveolar nerve andthe location of the teeth. In planning the os-teotomy site, distraction osteogenesis of themandible follows the principles of long-bonedistraction. The cross-sectional area of thebone formed in the distraction process (and toa great extent the strength of the bone gener-ated) is directly related to the cross-sectionalarea at the site of the osteotomy of the mandi-ble. The 4-year-old girl in Figure 4 with a hyp-oplastic mandible that was originally thoughtto be attributable to congenital facial micro-somia had been followed since the age of 1year. Her mother had undergone a series ofreconstructive procedures for a hypoplasticmandible, including costochondral graftingfor mandibular hypoplasia. Figure 4, above, alsoshows the congenital ear deformity. She alsohad a limitation in mandibular opening. Sur-

prisingly, computed tomography scanning of

the temporomandibular joint showed sagittalfractures through the condylar head on the leftand right, with a hyperplastic response on theright leading to bony ankylosis. The distractionwas performed with an osteotomy through theangle of the mandible and an external device,with a gain of approximately 40 mm. The post-operative computed tomography scan (Fig. 4,below) shows the dramatic difference betweenbone formation on the hyperplastic and nor-mal sides and illustrates the principle of boneformation being linked to the cross-sectionalarea of the osteotomy. The childs facial scarshave faded significantly.

These distraction cases highlight the appli-cation of bone distraction in the mandible witha goal of relieving airway obstruction that hadpersisted into childhood. This is a more com-mon problem than had been previously recog-nized.61 The advent of sophisticated polysom-nographic instruments has made this problemmore widely appreciated.62 It is unlikely thatthese cases could have been treated effectivelywithout the use of mandibular distraction os-teogenesis, considering the limited magnitude

FIG. 3. A child with Moebius syndrome, cleft palate, and severe mandibular hypoplasia.Internal distraction was used because only single-vector advancement was needed. The advance-ment was 25 mm, with conversions of class II to class III dental and skeletal relationships. (Left)Preoperative view showing a class II skeletal relationship. (Right) Postoperative view showing theconversion to a class III skeletal relationship.



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of the scalar movements that can be obtainedby conventional procedures. Nonetheless,these cases represent only one indication fordistraction osteogenesis of the mandible. Twospecial situations merit specific discussion:hemifacial microsomia (oculoauriculoverte-bral spectrum) and mandibular distraction forupper airway obstruction in Pierre Robinsyndrome.

Hemifacial microsomia is one of the mostcommon congenital anomalies, with an inci-dence of approximately one in 5000 births.Mandibular distraction lengthening has beenused in many cases of hemifacial microsomia toprovide jaw lengthening and even to create apseudotemporomandibular joint. The resultsin treatment of this disorder have been reward-ing. The treatment is limited to patients withappropriate bone stock distal to the dentitionfor creation of an osteotomy (Pruzansky grades

I and II).8,63 The primary advantages are thecreation of strong, well-vascularized bone andthe expansion of the soft-tissue envelope. Thisbone is much better for providing satisfactoryand durable expansion without resorption andloss of projection, as is often seen when costo-chondral grafts are used to reconstruct themandibular ramus. It is essential that a glenoidfossa or shelf be present to provide a buttressfor the distraction process; otherwise, one mustbe created. It is important to also appreciatethat the distraction process will not providecomplete correction of the deformity of hemi-facial microsomia, and appropriate planningfor maxillary osteotomy must be considered inthe overall treatment-planning process.64 Fur-thermore, milder cases of skeletal discrepancyin hemifacial microsomia can be appropriatelytreated successfully with conventional orthog-nathic surgery.

FIG. 4. A 4-year-old girl with severe congenital facial microsomiaand a strong family history of mandibular hypoplasia. Preoperativelateral view is shown (above, left). There was bony ankylosis of thetemporomandibular joint with condylar hyperplasia. (Above, right) Thelateral view of the patient near the end of the activation phase. (Below)After mandibular lengthening of 40 mm, postoperative computed to-mographic scan illustrates how new bone formation is a function of thecross-sectional area of the osteotomy.



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fracture of the angle of the mandible are sub-stantial. The demands on a framework used indistraction osteogenesis of the mandible areeven more substantial, and the use of threemonocortical screws on either side of the os-teotomy is unlikely to be sufficient in most

cases. In addition, the technique used duringplacement and fixation of the distraction de-vices must be precise and pristine. Whereas theconventional techniques used in facial fracturemanagement are useful as underpinnings, thetechnique used in placing distraction frame-works (internal or external) must be rigorouslyapplied. The basic principles of using newfresh burrs, using constant irrigation duringthe drilling process, and minimizing thermalinjury to the bone must be strictly followed inthis technique. Furthermore, the actual place-

ment of the pins and/or screws should be me-ticulous. If a pin or screw needs to be backedout, it is often better to drill a new hole andplace the pin/screw with a fresh placementthan to risk unstable and inadequate fixationthat will loosen and lead to failure of the dis-traction process.

In summary, distraction osteogenesis pro-vides a powerful and reliable technique forproviding well-vascularized bone in mandibu-lar reconstruction and providing simultaneousexpansion of the facial soft-tissue envelope.

These attributes have been used effectively intreating disorders that have been previouslynot optimally managed using the conventionaltechniques of orthognathic surgery, microvas-cular transfer, and nonvascularized bone graft-ing. The most frequent application has been intreating congenital deformities. The techniqueis reliable, but strict attention to technical de-tails of bone fixation should be observed.

MAXILLARY DISTRACTION AT THE LE FORT I LEVEL

Maxillary hypoplasia frequently occurs in pa-tients with cleft lip and palate. In approxi-mately 25 percent of these cases, the class IIImalocclusion is severe enough to require sur-gical intervention.71 Distraction at the Le Fort Ilevel has become the workhorse for managingthese severe maxillary retrusions commonly as-sociated with cleft lip and palate.7274 Beforethe advent of conventional Le Fort I osteot-omy, this difficult condition was treated fordecades by orthodontists using reverse facegears with heavy elastics. The result is usuallydisappointing, with advancements only in therange of 3 to 4 mm. The rate-limiting factor is

the extensive palatal scaring. This means thatto advance the maxilla, significant tensile forceis required. This tensile force on the maxillanecessarily produces corresponding pressureon the anchoring pads over the forehead andchin. The tensile force necessary to achieve

maxillary advancement appears to be highenough to produce sufficient pressure to causeskin necrosis under the anchoring pads. Toreduce this tensile force, the resistance to an-terior translation of the maxilla was decreasedby complete Le Fort I osteotomy. This surgi-cally assisted maxillary advancement used acombination of face mask, heavy elastics, andLe Fort I osteotomy and improved the magni-tude of advancement to the 5-mm range mea-sured at the maxillary incisor edge, which iscomparable to conventional Le Fort I osteot-

omy and advancement.75

The next improve-ment came about by providing a rigid anchor-age directly to the temporal region of thecranial skeleton using pin-retained hemi-haloand screw-generated pull in lieu of the elastics.This resulted in the current, versatile, externalmaxillary distraction system, which is capableof advancing maxilla for more than 30 mm.Polleys early reports showed average advance-ment of 11.6 mm with minimum relapse. Onekey component is the solid osseous anchorage.By using a torque wrench to tighten the trans-

cutaneous anchoring screws, the stress levels of8 psi for adults and 4 psi for children wereprovided as a guide.75 Because there is no needto establish maxillomandibular fixation, theoperation can be performed with oral intuba-tion. Because there is no need for plate-and-screw fixation, the osteotomy can be made veryhigh, at the level of the infraorbital foramen.This has two very significant salutary effects:avoiding damaging the developing permanenttooth follicles and providing high-level centralmidface advancement (Fig. 5). In addition, be-cause no plating is necessary, the operativetime is reduced. The conventional Le Fort Iosteotomy with plate-and-screw fixations hasbeen used extensively before distraction, but itis limited by the amount of advancement pos-sible and a significant relapse rate. The averageadvancement achieved by experienced sur-geons using conventional Le Fort I varies from4.5 mm to 7.8 mm for unilateral clefts and anaverage relapse of 4 to 40 percent, with largerrelapses seen in longer follow-ups.76,77

The need and the desire to close the ante-rior open bite during the advancement neces-



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sitate a downward vector. If the osteotomy isperformed at the Le Fort III level, the inevita-ble result is vertical elongation of the orbit.However, at the Le Fort I level, the downwardmovement is only limited by the aesthetics.Occasionally, too much gingival show rendersfurther clockwise rotation of the maxilla unac-ceptable. This occurs when the posterior as-pect of the maxillary segment has rotated infe-riorly because of the center of resistance beinghigher than the line of pull, thus creating aturning moment rotating the maxilla counter-clockwise. To lessen this, the vector of pullshould be made high. The risk of Le Fort Idistraction has all the risks of conventional LeFort I osteotomy and the added potential prob-lems related to the distractor.78,79 Significanthemorrhage can occur during Le Fort I osteot-omy, especially when the bone cut is carriedhigh posterolaterally into the pterygomaxillaryfissure. Blindness following Le Fort I osteot-

omy for distraction has also been reported.80

The external device is bulky and has been as-sociated with compound cranial fractures as aresult of minor trauma.81 In summary, thereare five significant advantages for distractionosteogenesis of the maxilla at the Le Fort Ilevel: large advancements, low relapse ratescaused by simultaneous soft-tissue expansion,decreased operating time, the ability to keepthe osteotomy high, and low incidence of det-rimental speech outcome resulting from velo-pharyngeal insufficiency.82

MAXILLARY DISTRACTION AT THE LE FORTIII LEVEL

Distraction techniques were first adaptedto the midface by craniofacial surgeons treat-ing children with craniofacial dysostosisassociated maxillary hypoplasia. Using a de-vice that penetrated the skin in the malarregion, Chin and Toth11,83 were the first to

FIG. 5. A teenager with a history of bilateral cleft lip and palate showing severe maxillaryhypoplasia. The preoperative lateral view is shown (above, left). The retropositioned maxillaprovided inadequate support of the lower lid. She was treated with hemi-halotype externalmaxillary distraction at the high Le Fort I level. The advancement was 18 mm and was stable at3 years. The high level of osteotomy (just below the infraorbital foramen) and amount of

advancement provided improved lower lid support with reduction of the vertical opening of thepalpebral fissure (above, right). (Below, left) The preoperative cephalogram. (Below, right) Thecephalogram at 3 years after the distraction.



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report distraction of the maxilla. Their de-vice was used to rapidly expand the Le FortIII osteotomy gap and then was left in placefor 6 months before removal. This initialreport was notable for the use of rapid ex-pansion (other surgeons using distraction

techniques were typically using a 1-mm/dayexpansion rate). Despite this accelerated ad-vancement, new bone formation was clini-cally evident after a 6-month consolidationperiod. The authors did observe significantbradycardia during the distraction phase intwo of their initial series of nine patients,presumably secondary to the oculocardiacreflex.

Shortly after this report, other surgeonsadapted similar distraction devices and rotatedthem 180 degrees to allow the devices to exit in

the less noticeable preauricular area. More im-portantly, the speed of distraction was sloweddown, which permitted faster bony consolida-tion, shortening the time needed for rigid re-tention.10,84Additional experience with Le FortIII distraction revealed that these devices werenot without some significant downsides. Onecommon problem is the difficulty in finding away to achieve a firm and stable attachmentbetween the skull and the malar region, partic-ularly when used in young children who havesmall and unstable zygomatic arches. Without a

reliable point of attachment, distraction willeither occur asymmetrically, lagging on theside that is not stable, or not occur at all (ifboth sides are unstable). Longer devices, with abroader plate for fixation, are a potential solu-tion to this predicament, but their use is notalways possible in younger children becausescrew placement in the maxilla may damagepermanent tooth follicles. Another problemwith the use of bilateral buried devices is theinability to change the vector of distractiononce the buried plates are in place.85 Difficul-ties frequently arise with the removal of thedevices, which tend to become imbedded inbone during the distraction process.

While many surgeons were in the process ofexperimenting with Le Fort III distraction, Pol-ley and Figueroa27,74 were working on an exter-nal halo distraction device, based on the orth-odontic face mask popularized by Delaire.86

This device was developed to treat the difficultadvancements of the Le Fort I segment associ-ated with a cleft lip and palate. Attachment ofthe external device to the Le Fort I segmentwas accomplished through the use of heavy

orthodontic wires. Their technique was foundto be extremely effective at advancing the mid-face, despite a scarred palate (average reportedadvancement, 11.7 mm). Moreover, these ad-vancements were accomplished with an ex-tremely low complication rate. Of all the avail-

able distraction devices, the hemi-halotypeexternal distractors are the most adjustable.Unhappy with the results of bilateral internaldistraction devices, Fearon84 adapted thishemi-halo distraction device for the treatmentof children with craniofacial dysostosisassociated midfacial deficiency. Modificationswere made in the standard Le Fort III osteot-omy to permit greater advancement, and thisexternal device was attached to the maxillathrough the use of a dental splint secured withmaxillary drop-wires. When compared with a

cohort of age-matched controls who had un-dergone the standard Le Fort III procedure,this initial series of Le Fort III hemi-halo dis-traction patients was shown to have a signifi-cantly greater advancement of the maxilla (av-erage advancement, 19 mm), without anyincrease in complications. Computed tomo-graphic scan analysis suggested that the facialprofile of patients who had undergone hemi-halo distraction was preferable to those whohad undergone a standard advancement. Thisimproved appearance is believed to derive

from the midline vector of traction associatedwith the use of the external device (by pullingthe centrally depressed face forward). The bi-lateral zygomatic-based, internal devices ad-vance the lateral aspects of the midface, poten-tially exacerbating the centrally deep midface.Other advantages of the halo distraction LeFort III over the standard procedure includedbetter correction of sleep apnea and shorteroperative times (secondary to the eliminationof the need for rigid fixation and the need toharvest cranial bone graft). As with distractingother sites of the facial skeleton, the resultsachieved with midfacial distraction are criti-cally dependent on the vector of distraction.The external halo distracter permits changesin the vector of distraction after placement,unlike buried devices. The halo distraction de-vice has also been reported to be a successfulsalvage technique for complications arisingfrom bilateral buried subcutaneous devices.85

Unlike distraction at the Le Fort I level, theLe Fort III distraction procedure is not anorthognathic procedure; it is a technique thatshould be used to reposition the malar emi-



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nences. It is important to avoid the temptationto try to close the anterior open bite that istypically seen in the craniofacial dysostoses, be-cause this can only be accomplished at theexpense of unnaturally lengthening the verti-cal orbital distance. The primary indication fordistraction of the Le Fort III is for the treat-ment of the hypoplastic maxilla in children

who have not completed facial growth (wheresome degree of overcorrection is desired)(Figs. 6 and 7). Distraction is seldom indicatedin the mature facial skeleton and should bereserved for planned advancements in excessof 1 cm in patients in whom scarring mayprevent accomplishing this with a standardprocedure. Lengthening of the maxilla (with

FIG. 6. (Above, left) A 712-year-old boy with Apert syndrome seen before distraction. (Above,right) Preoperative lateral view. Notice the significant midfacial retrusion. (Below, left) Frontal viewof the patient after Le Fort III osteotomy, with a rigid eternal distractor in place. (Below, right)Lateral view of Le Fort III distraction in progress. Notice the overcorrection.



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closure of the associated open-bite deformity)is best delayed until the middle to late teenageyears, when facial growth is complete. At thistime, the maxilla may be both advanced andlengthened with a combination standard LeFort III with Le Fort I.

In summary, distraction of the midface offersnumerous advantages: this technique permitsgradual expansion of the surrounding soft-tissue envelope, permitting a greater advance-ment than could be achieved with traditionalprocedures. Although the treatment time islonger, distraction is a shorter operation thateliminates the need for internal fixation andbone graft harvesting. With no metal plates leftbehind, secondary surgery is greatly facilitated,should the need for it arise. The disadvantagesof midfacial distraction include the following: asecond procedure is needed to remove thedevice, distraction is not always symmetric, thepostoperative orthodontic work is more chal-lenging, and the maxilla cannot be simulta-neously vertically lengthened if the distractionis at the Le Fort III level.

FRONTAL FACIAL ADVANCEMENT AND DISTRACTIONOSTEOGENESIS

An extremely important technique for re-constructing patients with syndromal midfacialdeformities is the frontal facial advancement or

monobloc osteotomy. Frontal facial or mono-bloc advancement for a patient with a syndro-mal midface deformity is often the most impor-tant procedure that a patient may undergo forrehabilitation of their congenital facial disfig-

urement. During this procedure, the foreheadand the face are literally sectioned or separatedfrom the skull base and repositioned three-dimensionally to correct the midface and fron-tal deficiencies. For appropriately selected pa-tients, this is an outstanding procedure thatcan yield dramatic morphological and func-tional results. The frontal or forehead advance-ment expands the anterior cranial vault, releas-ing intracranial hypertension, which iscommon as a result of the bicoronal synostosisin these patients. The forehead advancement isalso used for normalization of the frontal boneand forehead aesthetic projection. The orbitaladvancement with the monobloc osteotomymoves the entire functional orbit forward,normalizing its position, giving appropriatesupport to soft tissues about the orbital rimsand eyelids, and repositioning the orbital walls,allowing normalization of vectors of the ex-traocular musculature. In this procedure, ex-orbitism and exophthalmos are corrected, nor-malizing orbital aesthetics and improvingextraocular muscular imbalance. The mono-bloc osteotomy also advances the entire nose,

FIG. 7. (Left) Postoperative frontal view, 6 weeks after removal of the distractor. ( Right) Sixweeks after device removal, lateral view.



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including the nasal dorsum. This repositioningof the nasal structures in the sagittal planenormalizes nasal aesthetics and opens the nasalairway passage. In addition, advancement ofthe palate, maxilla, and zygomatic bones cor-rects a myriad of functional problems for these

patients, including opening the oral airway,correcting class III skeletal and dental relation-ships, and creating the proper oral and nasalcavities for improvement in articulation andspeech resonance. Although the functionaland morphological gains from this operationare essential for these patients, the monoblocosteotomy is perhaps the most feared osteot-omy in all craniomaxillofacial surgery. Stan-dard monobloc advancement procedures in-clude the frontal facial disjunction, intra-operative repositioning of the entire face and

forehead complex, extensive interpositionalbone grafting, and many points of rigid inter-nal fixation. In addition, in this operation, themidface is often stabilized with intermaxillaryfixation as well. The procedure can be a longone and requires extensive bone grafting andcarries the potential for major blood loss. Thegreatest problem with the monobloc osteot-omy with the traditional approach has beenthe extremely high incidence of postoperativeinfection. This incidence can range anywherefrom 10 to 50 percent, even in experienced

hands. When an infection does occur, it is nottypically a small problem but can includemajor intracranial abscesses, extensive bonedestruction, and even mortality. It is for thisreason that in the past many excellent centersworldwid e have avoided the monoblocosteotomy.

The application of distraction osteogenesisfor the monobloc osteotomy has revolution-ized this technique and has enabled this out-standing procedure to now be performed bymany surgeons worldwide.87 Frontal facial ad-vancement through distraction osteogenesisoffers many advantages over the traditionalmonobloc procedure. Some of these advan-tages include a decreased operative time, thefact that bone grafting is no longer required,elimination of internal fixation, decreasedblood loss, and decreased hospitalization. Thegreatest advantage for distraction osteogenesisand the monobloc osteotomy is the potentialreduction of the infection rate with this proce-dure.88With monobloc distraction, the osteoto-mized frontal and facial bones are not ad-vanced on the table at the time of the surgery.

This means there is no significant dead spacecreated in the anterior cranial fossa at the timeof the operation. The slow, gradual, rhythmicdistraction of the frontal facial region occurs ata rate that does not create a significant opendead space communicating the anterior fossa

with the nasal pharynx.89 In this fashion, as-cending oral pharyngeal contamination intothe intracranial space can be greatly reducedand controlled.

Monobloc midface distraction can be per-formed with an external distraction device orwith an internal device anchored along thezygomatic arch.90 Although both techniquesare used, many centers prefer an external dis-traction device for the monobloc advance-ment. External distraction allows completecontrol over the advancing midface and frontal

bone. Typically, with external monobloc dis-traction, anchorage points to the skeleton fol-lowing osteotomy are in the frontal bones bi-laterally and to the maxillary dental splint. Twopoints of fixation to the strong frontal boneand two points of fixation to the intraoralsplint allow four points of excellent control foradvancing and repositioning of the midface.The distraction procedure allows basically un-limited sagittal advancement of the midface,and rotational and vertical changes can bemade as the distraction process continues. Fi-

nal positioning of the midface can be titratedon the basis of individual aesthetic require-ments for the patient. The patients typicallywear the external halo for approximately 3months. After a 1-week latency period, activa-tion begins and continues over the next 2 to 3weeks. Consolidation of the advanced segmentis over the next 6 to 8 weeks. Confirmation ofconsolidation should be performed on a clini-cal basis, according to physical examination(Fig. 8).

The experience with internal distraction ofmidface monobloc osteotomies has been dis-appointing in some centers. The main prob-lem is the lack of control over the midfacesection. With internal distraction, the distrac-tion devices are secured at the time of surgeryand the final position of the midface cannot beadjusted during the course of distraction.Gauging precise vectors intraoperatively forplacement of the distraction devices is difficult.Internal distraction osteogenesis in the mono-bloc setting may have its greatest applicationfor those uncommon instances where midfa-cial advancement is required in infancy. One



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additional disadvantage of the internal distrac-tor is the need for and difficulty of removal.

Much still needs to be analyzed and learnedregarding monobloc distraction osteogenesis.As experience continues to grow, the tech-niques reliability, predictability, and very lowcomplication rate promise to be even moreimpressive. With greater experience, the pre-cise indications for monobloc midface ad-vancement with distraction osteogenesis willbecome elucidated.

CALVARIAL DISTRACTION OSTEOGENESIS

The calvaria is one of the last regions of thecraniofacial skeleton to enter clinical distrac-tion. However, the concept of expanding thecranium by tensile force has been reportedsince 1986.91 Several groups have adapted ab-sorbable plates and screws for the anchoragewhile using high-strength, nonabsorbable axialscrews for activation.92 This has made deviceremoval less cumbersome. Because soft-tissue

constraint is one of the theoretical rate-limitingfactors in the correction of craniosynostosis byconventional fronto-orbital advancements, dis-traction is ideal for overcoming this particularproblem. Research efforts have concentratedover the past several years on the developmentof totally implanted distraction devices.93,94

However, to date, there remains no approved,completely submerged cranial distraction sys-tem for clinical use in this country. A group inSweden led by Lauritzen has developed anddeployed implanted springs to achieve distrac-tion osteogenesis of the cranium. They usedcompressed springs to push apart the bonesegments following osteotomies. They re-ported the tensile force delivered by a spring tobe as high as 20 N. This type of distractiondiffers from all other types of distraction osteo-genesis in that the force is continuous and everreducing.95 Insufficient data exist at thepresent to evaluate this type of distraction os-teogenesis. The indications for distraction os-

FIG. 8. A 7-year-old patient with Crouzon syndrome showing severe midface

stenosis. (Above, left) Preoperative lateral view. (Below) During active rigid exter-nal monobloc distraction. (Above, right) One year after monobloc distraction.



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teogenesis of the cranium are not as clearlydefined as those for the other levels of thecraniofacial skeleton. One concern is the com-pressive force that is necessarily placed acrossthe patent sutures located anterior and poste-rior to the fused one undergoing distraction.

For example, in placing the distractor acrossthe coronal region, the ipsilateral lambdoid,frontozygomatic, and frontonasal sutures mustnecessarily undergo compressive strain. Howthis affects the behavior of these patent sutureshas not been well documented. The experi-ence with intrauterine constraint models cer-tainly indicates that, given enough compres-sion, sutures will fuse.96,97 The compressiveeffects on the temporomandibular joint havebeen reported.98 Similar concerns about thebordering joints have been expressed in the

orthopedic literature.99

CLINICAL OUTCOME AND COMPLICATIONS

Distraction osteogenesis is not performed bya large number of plastic surgeons. In a recentsurvey of 2476 surgeons in the United Statesand other countries, only 274 (11 percent)responded, and of this group, only 148 statedthat distraction is part of their practice.70 Theability of distraction to provide superior ad-vancements is clear. These advancements aremuch more resistant to relapse. Perhaps the

most significant point is that distraction osteo-genesis represents an emerging enabling tech-nology. It is a potent surgical tool and canproduce stable advancement exceeding 20 mmat every level of the craniofacial skeleton andsoft-tissue envelope, advancements that couldnot be easily achieved without distraction.However, at present, it is associated with animpressive complication rate. The reportedcomplication rates vary from 0 percent to 35.6percent to 60 percent.70,82,100 The potentialcomplications include the following: devicefailure; pin pullouts; infection; hardware expo-sure; damage to vital structures and adjacentjoints; inappropriate consolidation (prematureconsolidation or fibrous nonunion); and inap-propriate vector of distraction resulting inasymmetry, less-than-ideal occlusion, or frankmalocclusion. The orthodontic work after dis-traction is more extensive than after conven-tional orthognathic surgery. To provide someperspective, the clinical experience withcraniofacial distraction is comparable to, if notbetter than, the experience with distraction ofthe appendicular skeleton. The orthopedists

characterize the treatment course of distrac-tion osteogenesis in the long, endochondralbones as long, arduous, and painful. Theystated that the patients must be psychologi-cally robust.101 Finally, distraction should notand would not replace traditional osteotomies.

Movements that can be satisfactorily achievedwithout distraction osteogenesis should betreated with conventional, single-stage opera-tions.102 Faced with a rapidly increasing num-ber of new distraction devices, surgeons mustbe reminded of the learning curve so as tobalance between adopting newer, more effi-cient devices with which he or she has littleexperience and accumulating sufficient caseswith the existing systems to gain proficiency.

Jack C. Yu, M.D.Section of Plastic Surgery

Medical College of Georgia1467 Harper Street, HB 5040Augusta, Ga. 30912-4080

[email protected]

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Distraction Osteogenesis of the Craniofacial