chin deformities.pdf

Copyright @ 200 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.7

Chin Deformities

Judy Ward, MB, BS,* Silvio Podda, MD,1 Joe I. Garri, MD, DMD,* S. Anthony Wolfe, MD,*Seth R. Thaller, MD, DDS2

Miami, Florida, USA

Facial analysis for chin deformities evaluates theperioral structures independently and their rela-tionship to the entire face. Chin deformities in theabsence of malocclusion can be treated by agenioplasty. Patient evaluation and preoperativeplanning and the operative technique for anosseogenioplasty are outlined with clinical reportsto illustrate.

KeyWords: Genioplasty, chin, deformity, retrognathia

The chin, occupying its very prominentposition, is one of the elements of thecomplex facial structure that contributes tofacial balance and harmony.1,2 The har-

mony of the facial profile is determined in part by thesize, shape, position, and proportion of the chin withrespect to the other facial elements.2,3 The facialprofile has been divided into thirds, the lower thirdbeing determined by the size and shape of the chin.2,3

The patient who presents for facial-contouringsurgery has the goal of correcting imbalances of bothbony and soft tissues of the face to obtain facialharmony. The position and function of the lips isdetermined by the position and form of the under-lying dentition and chin and the relationship with theperioral facial mimetic muscles, particularly thementalis muscle, which contributes significantly tolabial competence being affected by change in chinposition and altered muscle forces.4 These patientsshould be evaluated in a systematic way, like anyother orthognathic patients.3,5

Many patients presenting with complaints of adeficient chin indeed have small mandibles and classII malocclusion and would benefit from orthodonticsand orthognathic surgery. For the purpose of thisdiscussion on genioplasty, we have assumed that

patients have a class I occlusion and hence do notneed surgery for correction of their malocclusion.

CLINICAL EVALUATION

The facial proportions must be considered andevaluated as a whole with detailed analysis of

chin position, height of the lower facial third,symmetry of lower facial third, labiomental sulcus,dental occlusion, soft tissue characteristics, and nasalrelationship.5Y7

Traditionally, the face has been evaluated interms of vertically equal thirds (Fig 1) and horizontalequal fifths (Fig 2). One should keep in mind that whatmay have been considered ‘‘ideal’’ proportions canchange over the years and certainly differs with raceand culture. Horizontal lines at the trichion, glabella,and menton provide landmarks to divide the face intoupper, middle, and lower thirds (Fig 1; Table 1).

Abnormal proportions require further evalua-tion of dental occlusion and the facial skeleton to ruleout short or long face syndromes or micrognathia.The lower third is further subdivided by the stomionat the point of contact of upper and lower lips.Stomium to menton should be twice the length thestomion subnasale distance. Further evaluation of thefrontal view is done by drawing a midsagittal line,which allows comparison of all paired facial struc-tures for symmetry.

When evaluating the face in profile, the relation-ship of the facial thirds also applies and is bestassessed along the Gonzalez-Ulloa zero meridian. Thisis a vertical line drawn perpendicular to the Frankforthorizontal line, which intersects the nasion (Fig 3). Inthe average face, subnasale should fall within this line.This zero meridian (also called the profile line) canalso be used to assess chin position, because the softtissue pogonionVthe most prominent point on thechinVshould lie approximately in a line throughsubnasale making a 10- angle with the zero meridian.In men, the chin should fall on this line or a couple ofmillimeters anterior, whereas in women, it should beon the line or a couple of millimeters posterior.16

It is also extremely important to assess the nose,because balance between the chin and the nose,especially in the profile view, affects overall facial

887

From the *Miami Children’s Hospital, Miami, Florida; the1Department of Plastic and Reconstructive Surgery, St. Joseph’sRegional Medical Center and Children’s Hospital, Paterson, NewJersey; and the 2Division of Plastic and Reconstructive Surgery,Jackson Memorial Hospital, Miami, Florida.

Address correspondence and reprint requests to Joe Garri, MD,DMD, 6280 Sunset Drive, #400, Miami, FL 33143; E-mail: [email protected]


harmony. If there is a discrepancy between theaccepted proportions between the chin and thenose, it is essential to figure out which of the twostructures or if both structures contribute to the

disharmony. Each structure must be evaluated by itsown and how they relate to each other. The idealnasal length (RTi) is equal to 67% of the middle facialheight (MFH) and equal to the chin vertical measure-ment Stomion to Mentum (SMe):

RT i = 0.67 MFH; RT i ¼ SMe

The noseYlipYchin plane is determined from avertical line drawn through the midpoint of RTi

touching the upper lip vermilion.14 Chin projectionshould touch this line in men and in women be 3 mmposterior to it and hence the upper lip sits at orslightly anterior to the lower lip (Fig 4).

The Rickett’s E-line assesses the overall align-ment of the nose, lip, and chin. It is drawn from the

Fig 1 Facial profile showing the division into upper,middle, and lower thirds. T = trichion, G = glabella, Sn =subnasale, Me = menton, FH = Frankfort horizontal, EFH =upper facial height, MFH = middle facial height, LFH = lowerfacial height.

Fig 2 Frontal view with division in equal fifths.

Table 1. Facial Profile With Frankfort HorizontalParallel to the Floor

Upper facial height (UFH) Trichion to glabella

Middle facial height (MFH) Glabella to subnasale

Lower facial height (LFH) Subnasale to mentum

MFH should be equal to or slightly (3 mm) less than the LFH.

Fig 3 Gonzalez-Ulloa Zero Meridian. FH = Frankforthorizontal, N = Nasion, Sn = subnasale, Pg = pogonion.Perpendicular line to FH which intersects N and Snrepresents the zero meridian or profile line. A line drawnat 10- to this should intersect with Pg in males or be slightlyanterior to it in females.

THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 18, NUMBER 4 July 2007

888


nose tip point pronasali to the most prominent chinpoint, the pogonion (Pg(s)Vsoft tissue pogonion).The E-line serves as a reference for the protrusion ofthe lips and should fall 4 and 2 mm from the upperand lower lips, respectively. Disparity can resultfrom malpositioned lips, nonoptimal tip projection,or a malpositioned chin16 (Fig 5). It is important thento assess each anatomic component separately todiagnose which component(s) is responsible for theimbalance.

RADIOGRAPHIC EVALUATION

On completion of a detailed clinical evaluation,confirmatory cephalometric analysis may be

done. Lateral and frontal skull x-rays are takenand skeletal points on the maxilla and mandibleare evaluated relative to each other and indepen-dently to the skull base. The important landmarkson the lateral cephalogram are detailed in Table 2(Fig 6).

Using cephalometric analysis, many parame-ters may be compared; the most pertinent ones areas follows:

SNA is the angle that relates the maxilla to the cranialbase (mean, 82 T 3-);

SNB is the angle that relates the mandible to thecranial base (mean, 80 T 3-);ANB is the angle that relates the jaw position relativeto one another. The angle should be zero or positiveto 2 mm.

Fig 4 Vertical line that intersects the midpoint of RTshould also intersect the upper lip and represent the Nose-Lip-Chin-Plane (NLCP).

Fig 5 Rickett’s E-line from the nasal tip; Pronasali = prnto the pogonion.

Table 2.

Sella (S) Center of the pituitary fossa

Nasion (N) Most anterior point at the nasofrontal junction

Point A Deepest midpoint of the maxillary

alveolar process between the anterior nasal

spine (ANS) and the alveolar ridge

Point B Deepest midpoint on the mandibular alveolar

process between the crest of the

ridge and pogonion

Gonion (Go) Most inferoposterior point at the angle

of the mandible

Gnathion (Gn) Cephalometric intersection of facial

and mandibular planes

Pogonion (Pg) Most anterior point along the contour

of the symphysis

Orbitale (Or) Lowest point on the inferior bony border

of the left orbital cavity

Menton (Me) Lowest point on the contour of

the mandibular symphysis

Porion (Po) Most superior extent of the

external auditory meatus

Mandibular plane Line joining gonion with menton

Frankfort horizontal plane Line joining the porion and orbitale

Aesthetic line Line joining tip of nose with the chin

CHIN DEFORMITIES / Ward et al

889


A patient with a class I occlusion will have normalangles and attention can be turned to determiningthe ideal chin point.

Holdaway’s Angle

Nasion-B point line intercepts forms an angle of 7 to 9with a tangent to the upper lip and chin. If the ANB

angle is enlarged or reduced, the difference iscorrespondingly added to or subtracted from the Hangle.18

CLASSIFICATION OF CHIN DEFORMITIES

An extensive classification system of chin defor-mities was described by Guyuron,15 which

includes:

Class I: macrogeniaV(a) horizontal, (b) vertical, (c)combination of both;Class II: microgeniaV(a) horizontal, (b) vertical, (c)combination of both;Class III: combinedV(a) horizontal macrogenia withvertical microgenia, (b) horizontal microgenia withvertical macrogenia;Class IV: asymmetric ChinV(a) short anterior facialheight, (b) normal anterior facial height, (c) longanterior facial height;Class V: witch’s chinVsoft tissue ptosis;Class VI: pseudomacrogeniaVnormal bony volumewith excessive soft tissue; andClass VII: pseudomicrogeniaVnormal bony volumewith retrogenia secondary to excessive maxillary growthand associated mandibular clockwise autorotation.

DETERMINATION OF SURGICAL PROCEDURE

After facial analysis is complete, a surgical plan isformulated based on aesthetics (guided by facial

analysis and cephalometric measurements), whichmay involve changing the chin position in the ver-tical, horizontal, or lateral planes.1,11,13 The desired

Fig 7 Osteotomy line for a genioplasty.Fig 8 Sliding genioplasty. Genioglossus and geniohyoidremaining attached to the inferior border.

Fig 6 Cephalometric tracing.


890


quantitative movement of the soft tissue chin pointshould be decided on preoperatively and based onthis, the necessary bony movement needed toproduce a reciprocal soft tissue change is calculated.

Depending on the movement made on the bonymenton, the corresponding soft tissue change willvary. With advancement genioplasty, the ratio of softtissue advance at the level of the gnathion has beenpredictably calculated to be 0.9:1. Additional benefitsinclude increase in the submental length and cervico-mental angle, improved relationship of the lower lipto the mandibular incisor with less eversion, andoverall advancement of the genialYtongueYhyoidposition, which can have a functional effect inindividuals with nocturnal snoring.17 The soft tissuesof the chin follow vertical lengthening bony move-ment with a 1:1 ratio. Reduction osteotomies, how-ever, have a less predictable effect on the soft tissuesbecause of the redundancy of the soft tissue that is

created. Horizontal reduction results in a soft tissuechange, which follows the ratio of 0.6:1, whereas forvertical reduction, the ratio is 0.25:1.17

SURGICAL TECHNIQUE

The techniques that can be used to change theposition and/or the size of the chin are essen-

tially of two types1,9: bone contouring techniqueVgenioplasty and use of alloplastic chin implants. Thefirst option, chin osteotomy or osseous genioplasty, isdiscussed here. A genioplasty may be performed as asingle procedure or in conjunction with orthognathicor other facial cosmetic procedures as part of an over-all treatment plan to optimize facial aesthetics andharmony.1,8,11,13

A genioplasty is performed preferably undergeneral anesthesia, although sedation and localanesthesia can be used. The patient is positioned

Fig 9 Jumping genioplasty.

Fig 10 Interpositional bone grafting.

Fig 11 Wedge genioplasty.

Fig 12 Stepladder genioplasty.


891


supine; a donut or headrest should not be used toallow for adequate head extension. The surgeonstands at the head of the table where contour andsymmetry of the chin is best appreciated.

Local anesthesia with a vasoconstrictor is infil-trated below the mucogingival sulcus extendingposteriorly to the second premolar. The incision isthen performed with a needle tip Bovie or a surgicalknife on the free mucosa of the vestibule, leaving acuff of tissue for closure. Optimal exposure isparamount, so the incision extends from cuspid tocuspid. The incision is extended perpendicularlythought the mentalis muscle and periosteum, whichis then striped with an elevator to expose the anteriorborder of the mandible.

Particular care is taken in exposing the inferiorborder until the mental foramen is clearly identifiedand the mental nerve protected.10 Normally theinferior alveolar nerve exits the mandible through

the mental foramen, which is located just below thesecond premolar equidistant from the superior andinferior border of the mandible. After positiveidentification of the neurovascular bundle, it isimperative to perform a dissection below it, becausethe genioplasty osteotomy extends well posteriorlyon the mandible from this point.

The midline of the mandible is then marked bycomparison to the dental midline and other facialstructures, most commonly with the use of anoscillating saw to carve a permanent vertical markin the cortical bone. The oscillating saw is then usedperpendicular to this line to make an osteotomy ofthe anterior mandible full-thickness to the lingualcortex. Then the reciprocating saw is used tocomplete the osteotomy laterally. The level of theosteotomy must be at least 5 mm below the canineroot11 and when extended laterally 6 mm below theinferior to the mental foramen.20

Fig 13 Patient presented with a deficient, asymmetrical chin for which a centering, advancement genioplasty wasundertaken. (A) - Frontal, preoperative; (B) - Frontal, postoperative; (C) - Lateral preoperative; (D) - Lateral, postoperative.

Fig 14 Retrognathia with evidence of mentalis strain preoperative. An advancement genioplasty was undertaken with amuch improved facial profile and mentalis function. (A) - Frontal, preoperative; (B) - Frontal, postoperative; (C) - Lateral,preoperative; (D) - Lateral, postoperative.


892


When cutting in the area of the inferior border ofthe mandible, the surgeon’s nondominant hand isused to palpate the tip of the blade, thus ensuringthat both cortical walls have been fully cut. When allthe osteotomies have been completed, the periostealelevator is then placed at the osteotomy site inthe midline and, with a torquing motion, the twosegments of the bone are separated. Once theseparation is done, the distal segment shouldmaintain its lingual attachments that consist of thetwo muscles genioglossus and geniohyoid (Fig 7).These muscles need to be stretched at this point ifadvancement is planned. It is recommended thatthe pogonion not be advanced beyond a perpen-dicular dropped from the lower lip because thisresults in a markedly exaggerated appearance ofthe chin.

The distal segment is then placed in the desiredposition and the inferior border checked for anysharp edges or steps that are smoothed with a rasp.Rigid fixation is achieved with a bone plate orscrews. Plates can either be prefabricated to differentlengths of chin advancement or regular straightplates, which are bent to fit in the operating room.For screw fixation, 2-mm bicortical screws areusually used, of which two are needed to attainadequate fixation.

When vertical shortening is anticipated, twoosteotomies are performed following markings atthe level of the B point of the mandible and a secondinferiorly on a parallel plane. The distance betweenthe parallel osteotomies should be calculatedpreoperatively and should be equal to the amountof desired reduction. The inferior osteotomy has to beperformed first such that the superior one is

performed on a stable segment. After the osteotomieshave been completed, the intervening bone fragmentis removed and the two segments placed in theproper position and the fixation applied. For increasein the vertical dimension, a singular osteotomy isnecessary and an intervening bone graft is placed inbetween the two bony segments.

Once the fixation is successfully completed, thesurgical site is copiously irrigated and the soft tissuesare then closed. This can be done in two layers, firstthe muscle layer followed by the mucosa or just asingle layer with resorbable sutures. An externaldressing is not necessary in these cases, but manysurgeons advocate the use of foam tape around thechin to maintain soft tissue stability and reduce thepostoperative edema.

The genioplasty procedure is further differen-tiated and classified depending on the variation oftechniques, the reciprocal movements of the man-dible segments, and the final result that needs to beachieved.1,11Y13

The classification follows:

1. In the sliding genioplasty, the osteotomy segmentslides anteriorly and the lower third verticaldimension is not modified (Fig 8).

2. In the jumping genioplasty, the caudal segment ismoved anteriorly and placed in front of themandible, almost like an implant. The lower softtissue attachments of the segment should bepreserved to avoid bone resorption. This nomen-clature was actually used for the first time byGilles and indicates the attempt to improve thesagittal projection of the chin and decrease theheight of the lower facial third24 (Fig 9).

Fig 15 27-year-old male who desired a stronger chin underwent a 5 mm advancement genioplasty concomitant withsubmental liposuction. (A) - Frontal, preoperative; (B) - Frontal, postoperative; (C) - Lateral, preoperative; (D) - Lateral,postoperative.


893


3. In the graft genioplasty or interpositional genio-plasty, the advancement is achieved with theinterposition of bone graft between the mandiblesegments to advance the chin as well as increasethe lower facial height (Fig 10).

4. In the wedge genioplasty, the anteroposteriordimension and projection of the chin is increasedand the height of the lower facial third isdecreased (Fig 11). Two horizontal osteotomiesparallel to each other and to the occlusal plane areperformed and, after the caudal cut is made, thesegment between the osteotomies is resected. Inthis case, you reduce the lower facial third heightconsiderably. It is important to let the patientknow that a certain degree of soft tissue ptosismay occur.

5. In the case of oblique genioplasty, the osteotomyis performed obliquely on the sagittal plane,allowing the distal fragment to slide anteriorlyand superiorly if the posterior aspect of the cut ismore caudal. In case the posterior aspect of the cutis more cephalad, the distal fragments slideanteriorly and inferiorly.

6. The stepladder/two-tiered genioplasty techniqueis used instead in cases of important sagittaladvancement without significant modification ofthe lower facial third height. Two osteotomies areperformed and the lower segment is advancedsagittally over an already advanced proximalsegment (Fig 12).

7. Finally, there are a special group of procedures,in which the vertical and horizontal asymmetryare corrected and these are called asymmetricgenioplasty. Normally, a lateral wedge of thebone is resected on the longer side and used inthe contralateral side. The midline is also shiftedto the center of the facial axis during thisprocedure.

Figures 13, 14, and 15 show patients who haveundergone genioplasty surgery with stable post-operative results.

REFERENCES

1. McCarthy JG, Kawamoto HK Jr, Grayson BH, et al. Surgery ofthe jaws. In: McCarthy JG, ed. Plastic Surgery. Philadelphia:WB Saunders, 1990:1188Y1200

2. La Trenta GS. Facial contouring. In: Rees TD, La Trenta GS,eds. Aesthetic Plastic Surgery, Vol. 2. Philadelphia: WBSaunders, 1994:809Y819

3. Gonzalez-Ulloa M. Quantitative principles in cosmeticsurgery of the face (profileplasty). Plast Reconstr Surg 1962;29:186Y198

4. Michelow BJ, Guyuron B. The chin: skeletal and soft-tissuecomponents. Plast Reconstr Surg 1995;95:473Y478

5. Rakosi T. Cephalometric Radiology. Philadelphia: Lea &Febiger, 1982:78Y89

6. Ferraro JW. Cephalometry and cephalometric analysis. In:Ferraro JW, ed. Fundamentals of Maxillofacial Surgery. NewYork: Springer, 1997:234Y236

7. Vig K, Ellis E. Diagnosis and treatment planning for thesurgical orthodontic patient. Clin Plast Surg 1989;16:645Y658

8. Proffit WR, White RP Jr, Sarver DM. Treatment planning:optimizing benefit to the patient. In: Proffit WR, White RP Jr,Sarver DM, eds. Contemporary Treatment of DentofacialDeformity. St Louis: Mosby, 2003:172Y244

9. Ellis E. Accuracy of model surgery: evaluation of an oldtechnique and introduction of a new one. J Oral MaxillofacSurg 1990;48:1161Y1167

10. Rajchel J, Ellis E, Fonseca RJ. The anatomical location of themandibular canal: its relationship to the sagittal ramusosteotomy. Int J Adult Orthod Orthognath Surg 1986;1:37Y47

11. Kawamoto HK Jr. Osseous genioplasty. Aesthetic SurgeryJournal 2000;6:509Y518

12. McCarthy JG, Ruff GL, Zide BM. A surgical system for thecorrection of bony chin deformity. Clin Plast Surg 1991;18:139Y152

13. Cohen SR. Genioplasty. In: Achauer BM, Eriksson E, GuyuronB, et al, eds. Plastic Surgery: Indications, Operations andOutcomes, Vol 5. Philadelphia: Mosby, 2000:2683Y2703

14. Byrd HS. Rhinoplasty. Selected Reading in Plastic Surgery.2001;9:7Y9

15. Guyuron B, Michelow B, Willis L. Practical classification ofchin deformities. Aesth Plast Surg 1995;19:257Y264

16. Hom DB, Marenette LJ. A practical methodology to analyze facialdeformities. Otolaryngol Head Neck Surg 1993;109:826Y838

17. Roszkowski MJ. Soft tissue changes associated with orthog-nathic surgery. Oral and Maxillofacial Surgery KnowledgeUpdate, Vol 1, Part II 1995:57Y73

18. Cohen S. Genioplasty. Plastic Surgery Indications, Operations,and Outcomes. St Louis: Mosby, 2000

19. Gilles H, Millard DR Jr. The Principles and Art of PlasticSurgery, 1st ed. Boston: Little and Brown, 1957:361Y362

20. Ousterhout DK. Sliding genioplasty, avoiding mental nerveinjuries. J Craniofac Surg 1996;7:297Y298


894

chin deformities.pdf

Documents