CHAPTER 22

The Transoral Chin Correction

22.1 Historical Background

When I started my training in maxillofacial surgery, in very severe cases only did surgical correction of the chin anomaly seem to be indicated. In the retrogenia cases, a bone graft was onlayed via a submental ap­proach. It often produced, temporarily, quite a pleasing enlargement of the chin prominence but at the expense of possible infection and a submental scar which could be rather unsightly. And, of course, also there was the disadvantage of a second operation at the donor site for the bone graft. But there was another great disadvan­tage. It was the amount of resorption of the bone graft which followed within a year. And it was not easy to shape it so that it would fit nicely against the chin sur­face and it was not easy to fix it either. Often enough the bone graft was just placed onto the cortical surface of the chin, with some cancellous bone placed around the contact area. The experience with these onlay grafts led me to formulate the principle: "Cortical bone shrinks like a mushroom in the sun, and cancellous bone melts away like ice cream when used as an onlay graft for con­tour correction "(Principle Nr. 18).

Besides autogenous bone, autogenous rib cartilage was used and also preserved bovine cartilage. The first again had the disadvantage of the need for a second op­eration site on the patient and the second quietly disap­peared.

Several types of alloplastic materials were used, such as titanium mesh (K.H. Thoma 1948) or acrylic. At the Maxillofacial Unit of Graz University, we had a number of different sizes and shapes in stock. We also tried to form them preoperatively in wax according to the patient's requirements and have them processed in acrylic, and implanted them also from a submental ap­proach. It was not really successful. Too high an inci­dence of infection, secondary displacement, dehiscence of the suture line etc. did not allow it to become a prac­tical procedure. The prefabricated silastic chin implants did much better but also often with too high an inci­dence of problems. It could even erode into the bone and come to rest against the roots of the patient's front teeth due to the pressure from the advanced soft tissues. J.M. Converse (1964) used the lower border of the re-

truded much-too-high (deep) chin as a free onlay graft, via an oral approach.

When I came to deal with such a case of hyper- and/ or hyporetrogenia, I saw on the cephalogram that I could slide the lower border of the chin forwards and upwards, leaving it pedicled on the digastric and geni­ohyoid muscles. As I then did all mandibular symphysis and body fractures via the oral route, I also did chin ad­vancement transorally, using J.M. Converse's degloving technique.

I cut off the lower border of the chin with a Linde­mann bur. I was accustomed to using that easily break­able instrument from experience with it in other osteoto­mies. I directed the osteotomy line from low posteriorly to higher anteriorly. I could easily pull it forwards by 10 mm, pedicled on the geniohyoid muscles. In that first case I fixed the advanced chin horseshoe with a strong perimandibular Supramid thread on each side over an acrylic dental splint, so as to permit removal of the thread after three weeks (H. Obwegeser 1957) (Fig. 99a). The op­eration went without any problems and no postoperative complications. The result was very pleasing (Figs. 99b-e).

I reported my enthusiasm for this transoral chin cor­rection procedure to my teacher Trauner and asked him by letter whether he knew of any literature on this tech­nique. He replied no and wrote "but it is so simple that it seems impossible that nobody else had had that idea be­fore". Later, I used direct bone wiring for fixing the ad­vanced horseshoe in the new position.

Soon, I learned that in some cases I had to make a more Roman arch out of a Gothic-shaped lower border or vice versa. And I also learned that, depending on the direction and shape of my bone cut, I could increase or decrease the chin height and could also correct a chin asymmetry (Fig. 99f).

In order to publish this valuable new technique more extensively (H. Obwegeser 1958) I tried to find anything similar in the literature. I found that 0. Hofer ( 1942) had suggested sliding the inferior border of the chin for­wards, from an extraoral approach leaving it muscle pedicled on the platysma, digastric and the geniohyoid muscles. His operation was performed on a cadaver us­ing a rather large bone saw (Fig. 99g).

Later, my friend 0. Neuner (1965) suggested doing a double-step advancement. I liked that idea and obtained

H. L. Obwegeser, Mandibular Growth Anomalies© Springer-Verlag Berlin Heidelberg 2001

418 CHAPTER 22 The Transoral Chin Correction

good results with it. In an appropriate case one can even perform a triple-step advancement (H. Obwegeser 1974). In order to handle the chin piece more easily, I started to free it from all musculature, trimmed and shaped it according to the requirements and then fixed it with direct wires. In a follow up investigation it was found that, on average, 50% resorption occurred, how­ever, some of it was transformed into soft tissue, de­creasing the amount of loss of contour in front of the bony chin. After that, we always left the advanced inferi­or chin border muscle-pedicled again, even in the dou­ble-step cases. A follow up study of these cases proved that there was only, on average, 10% resorption and even that amount was often found to be transformed into soft tissue, thus producing the planned amount of prominence advancement.

In double or even triple-step advancement, I often used deep frozen cancellous cadaver bank bone to fill the steps between the outer wall of the alveolar pro­cess and the advanced chin prominence. But even with­out it, I often found new bone formation in that step area.

22.2 My Final Method

There has not been much change since my publication in 1957 and 1958, except that the surgery has become less radical as far as bone exposure is concerned. If the chin advancement only is all the patient wants, it can be done as an outpatient procedure, under bilateral block and local anaesthesia. But there is no difference in the

Fig. 99a-c. Transorai chin correction. a Diagrammatic illustration of first case of t ransoral sliding g enioplasty (from H. Obwegeser 1957). b, c Radiographs of first case of transoral chin advancement (from H. Obwegeser 1957, 1958)

22.2 My Final Method 419

f

Fig. 99d-f. Transoral chin correction. d, e Profile views of first case of chin advancement, before and I year after surgery. f Schematic il­lustration of the various directions of the cut for achieving a sliding genioplasty to reduce or increase the vertical height of the chin prominence or to correct chin asymmetry and the radius of the chin prominence (from H. Obwegeser 1957, 1958, 1971)

operating technique whether the chin correction is per­formed under general or local anaesthesia.

The vestibular incision is made approximately 5-8 mm labial to the depth of the vestibulum, at a right an­gle to the mucosal surface only, and then directed hori­zontally to the alveolar process. The periosteum is in­cised from underneath the mental foramen as far back as necessary, from one side to the other. The direction of

the bone cut has to be determined preoperatively on a tracing of the lateral cephalogram, on which the desired profile line has been drawn. According to that planning, the lower border of the chin has to be moved forwards for correction of a retrogenia or upwards, if necessary even by excision of a strip of bone below the teeth, for correction of a severe hypergenia, or in a cranially con­vex curvature for the correction of a hypo- and retroge-

420 CHAPTER 22 The Transoral Chin Correction

f' : ~ .. ) \

.. ~.... .... 1 ~~~~

. . \

Fig. 99g, h. Transoral chin correction. g 0. Hofer's suggestion for chin advancement, performed on a cadaver (from 0. Hofer 1942). h Diagrammatic illustrations of various possibilities for reducing the size of the chin

nia. The existing shape of the chin and the result desired dictate the osteotomy cut. The tracing with the desired profile line permits the use of a transparent foil which is cut according to the existing shape of the bony chin to simulate the osteotomy line necessary to achieve the planned result. If more than 8 mm advancement is nec­essary, a double-step advancement should be planned. It gives a better result when each step is not too large. If there is some bone available to place on the step it is def­initely an advantage. If there is a rather large step, the soft tissue line will show it in the final result as the soft tissue of the chin may be fixed into that step. The more the chin has to be advanced, the further back will I go with my bone cut, in particular when performing a dou­ble- or triple-step advancement. The mental nerve must be well protected. However, the complete degloving procedure belongs to history. The more soft tissues are left attached to the piece of bone which is to be moved, the less resorption of the moved segment will take place.

I personally like to use a reciprocating saw with thin disposable blades. My former co-worker, A. Triaca, does all osteotomies, even those for chin correction, with a

rather short, hard steel bur normally used in dental la­boratory work (Maillefer Nr. 540). He does not free the prominence of the chin from the investing soft tissues completely. He leaves the inferior part of the mentalis muscle attached to it. He only frees the lower border in the area where the osteotomy reaches it. He resects the lingual rim of the detached chin prominence with the attached musculature using the same bur in order to re­duce its backwards pull when the chin is moved anteri­orly. This seems much better than dissecting the inser­tion of the musculature.

The technique for enlarging or reducing the width of the horseshoe-shaped lower border remains the same as published in 1958. However, it is not all that easy to ex­cise a triangular piece of it at its posterior surface in­cluding the mental spine, and yet leaving some genioh­yoid musculature in that area adherent. For that, the just mentioned resection of the lingual cortical rim helps to solve the problem.

When there is need to correct a hypogenia, again the desired profile line tracing is used to ascertain whether an upwardly-curved, almost semicircular bone cut will achieve the planned result or whether the sandwich

22.3 Principal Complications, How to Deal with Them and How to Avoid Them 421

technique {J.M. Converse 1964) has to be used to achieve the necessary height increase.

The asymmetric chin prominence, not only present in cases of hemifacial microsomia but also in condylar hyperactivity cases, deserves special consideration. H. Sailer (1985) has suggested his so-called chin propeller technique. Another simple way is to cut the detached lower border into two unequal segments, using the sym­physis as the site of the cut. Then the longer part is shortened so that from medial to lateral both are equal in length. Both segments are fixed together and to the chin.

Chin reduction is less often necessary than the cor­rection oflack of its vertical height or horizontal length. The type of correction of surplus of the bony chin de­pends on its existing and the desired shape (Fig. 99h). To correct a horizontal surplus by trimming it off with a bur seems the easiest way. In my hands that very rarely produced a pleasing result. Almost always the promi­nence became too rounded. A much more pleasing re­sult is achieved by a rather vertical strip excision. If the chin is too high (deep) in its vertical dimension prefer­ably a wedge shaped piece will have to be excised, as shown in the illustration (H. Kole 1970).

The fixation of the advanced chin nowadays varies from surgeon to surgeon. Lag screws are rapidly insert­ed and quite sufficient. However, they do not need to be so strong that a horse could pull on them! Screws of 1.5 mm diameter should suffice. Others prefer specially designed plates. And it can still be done with wires if necessary, as I did for over 30 years!

The soft tissue surplus in the chin region is more difficult to correct than are the bony abnormalities. A certain amount of contour reduction can be achieved by reducing the underlying bony chin. But there are cases which definitely need soft tissue excision, skin as well as subcutaneous tissues and musculature (Smith 1985).

The method of managing and closing the incision line is important. I have often been asked what I do to prevent suture dehiscence which I have sometimes seen in patients of my trainees. There are a few important points to be observed. It begins with the incision. The knife must cut the mucosa at a rightangle to the muco­sal surface. That permits good adaptation of the wound edges, much better than when the knife cuts through the mucosa obliquely. Secondly, with the subsegment verti­cal cut to the chin area, quite a bit of musculature re­mains on the chin. When closing the wound, this per­mits a better bite with the needle than when mucosal edges only are approximated. Thirdly and most impor­tant, is the handling of the edges of the mucosa. It is bet­ter not to use toothed forceps to hold the edges. Fine single hooks do less harm. Next is the type of suture ma­terial to be used. No hydrophilic thread is any good. It absorbs saliva and conducts infection into and under­neath the approximated edges.

For more than 45 years, I have preferred "Supramid", a suture material which is not as stiff as a monofilic thread as it consists of a great number of very fine fila­ments which are covered by a layer of non-hygroscopic material. The type of suturing is also important. Some­times I even used submucosal catgut sutures. I gave it up. They are too difficult to insert. I prefer a continuous suture, changing between a vertical mattress type to an occasional ordinary continuous suture. Very gentle ad­aptation is important. Postoperatively, I compress the soft tissues towards the chin, particularly above the ad­vanced part, with some slightly elastic strips.

Since I published this transoral chin correction in 1957 and 1958 it has become a widely used procedure, also in connection with elongation osteotomies of the mandible (see Figs.l3+ 14). J.M. Converse, who had nev­er done a sagittal splitting of the rami until we met, asked me twice where and how I obtain the necessary quantity of skin cover. I told him that, if necessary, I mo­bilize the periosteum bilaterally with the investing soft tissues around the chin and all the way back beyond the angle of the jaw.

22.3 Principal Complications, How to Deal with Them and How to Avoid Them

22.3.1 Problems During Surgery

Bleeding: Bleeding from the incision of the mucosa is rarely a real problem. Occasionally only a small vessel may become troublesome. Elecro coagulation will stop it.

More troublesome bleeding may arise from a vessel within the musculature which is attached to the lingual side of the chin. The reciprocating saw can cut too deep­ly into these muscles. The bleeding vessel cannot be seen as long as the chin prominence is not detached. Thereafter there is good access to clip or just coagulate the vessel. Bleeding occurs more often in a double- or even a triple-step advancement of the lower border of the chin. It should not be a reason for detaching the musculature from the chin horseshoe.

The Mental Nerve. It can be damaged when mobilizing the periosteum or when performing the bone cut with a saw or a rotating bur. Pressure or pull on the nerve may cause temporary hypo- or anaesthesia which recovers within a few weeks or months. Damage to the nerve by a bone cutting instrument may be due to partial or com­plete cutting of the nerve. In the first instance sensibil­ity may return after 6 to 24 months, in the second, nerve anastomosis before wound closure may help, but only very occasionally. When the nerve is cut or pulled out of the foramen complete anaesthesia of that side of the lower lip will result. Almost always, in some cases after

422 CHAPTER 22 The Transoral Chin Correction

one or two years, in other cases even later, some kind of sensation is felt by the patient. Some will even forget their numbness of the lower lip and tell the examining doctor that everything is normal. And yet, when careful­ly checked, normal sensation cannot be proven.

In some cases, in particular when infection at the site of the nerve has occurred, intractable pain will result. It is a constant type of neuralgia like a neuritis, in spite of complete anaesthesia of the lip. It is called "anaesthesia dolorosa''. Nothing seems to be able to cure that pain, not even high doses of vitamin Bl2, nor injection of concentrated alcohol into the mental foramen and also not the ablation of the whole mandibular nerve from the lingula to the mental foramen. For that type of an­aesthesia dolorosa I do not have any other explanation but that it exists on the basis of nerve vessels. Even in­jections of local anaesthetic cannot eliminate the pain completely. They reduce it only for a short while.

Wrong Direction of the Bone Cut. It is not uncommon. The cause for it is inexact planning. When it happens try to make the best of the situation!

Problems With Fixation. They can hardly be expected when the chin prominence has to be fixed as one single piece of bone into the planned place, independent of whether the surgeon uses wire fixation, as we did for thirty years, or lag screw or plate fixation. Fixation be­comes more difficult when a two- or three-step reposi­tioning is planned and even moreso when the detached horseshoe has to be separated into two pieces either for reasons of asymmetry or in order to make a Gothic arch out of a Roman arch or vice versa. However, with direct screw fixation and with plates and screws this should not cause any real problem.

Losing a Piece of a Bur or a Saw Blade. It happens occa­sionally, but not when non-breakable saw blades are used. One should try to find the foreign body, but with­out risking detachment of the genioglossus and genioh­yoid muscles from the bony horseshoe. Rather leave it and inform the patient. It will rarely give rise to abscess formation. If it does it must be removed.

22.3.2 Problems After Surgery

Infection With Slight Pus Discharge. This is seen rather often. In such cases, we routinely rinse the operating field twice a day, through the incision line in between the sutures. After a week or so the pus production will stop. If not, one will have to think of a forgotten gauze in the operating field or sequestration of the repositioned bone segment. In both situations the cause must be re­moved and the operating field washed thoroughly with a strong antibiotic solution and if possible, after spray-

ing some antibiotic powder over the whole operating field, the wound is closed again.

Suture Dehiscence. It seems to be a rather common problem. Secondary closure will rarely be successful. Daily rinsing with antibiotic solution and covering the wound with a vaseline gauze strip which is covered and soaked on its surface with an acetone glue. Once, on my ward round, I found quite a number of suture dehis­cence cases after both sagittal splitting of the rami as well as after chin correction only. I was astonished and asked the trainee in charge what he thought of this. His reply was short and clear: "Don't you know, professor, that this is quite common and does not matter?". It means that it almost always heals without great prob­lems, however, with additional treatment and costs for the patient. I prefer to prevent it by proper suturing as mentioned in the section "Closing the Incision Line".

Relapse. That means displacement of the repositioned horseshoe. It can happen within the first three weeks, rarely later. It is due to inadequate fixation. I have heard of it, but never experienced it myself. A radiograph will give the information as to what has happened. Proper refixation is the necessary treatment.

Resorption. It will always take place to a certain extent, but maybe without spoiling the final result, since in most cases of muscle pedicled chin correction the average re­sorption of 1 Oo/o is replaced by fibrous tissue. In cases when the resected chin prominence is repositioned as a free bone graft and not muscle-pedicled, the average re­sorption will be about SOo/o, as mentioned before. A part of that will again be replaced by fibrous tissue.

Unaesthetic Chin-neck Contour. That can easily occur when it already existed preoperatively and the chin prominence was moved forwards, pedicled on the pla­tysma muscle. In these cases, I want to reposition the horseshoe pedicled on the hyoid musculature only, in­dependently of whether it is a one-, two- or three-step advancement. Then the chin-neck line will always be better than when the horseshoe is left pedicled on the platysma muscle also.

Unsightly Upward Retraction of the Skin Behind the Advanced Prominence. That can occur when it already existed before surgery as an ugly skin fold and the chin prominence has been brought forwards quite a dis­tance. Although the skin will be rather tight behind the chin, in spite of that, an empty space can be palpated where the upward retraction was before surgery. In these cases I fill that area up with thin slices of !yo-car­tilage via the oral access before closing the vestibular in­cision and obtained excellent results. Any other materi­al for contour correction may be just as good.

22.4 Deep Frozen Bank Bone

The type of material to be used to fill gaps in the bone is worth mentioning in detail, as the same need exists not only for the sandwich chin enlargement but also for the Le Fort !-advancement or maxillary vertical height in­crease, etc .. Several materials have been used to fill such gaps. Best of course is the patient's own bone. Again deep frozen cadaver bank bone was used for the rather rare case of sandwich chin enlargement and, as men­tioned earlier for maxillary advancement, with very good results as long as the defect was not larger than 10 mm. At that time we did not bother about tissue com­patibility between recipient patient and donor. We nev­er experienced any problems with this. We removed as much cancellous bone from a donor cadaver as we

22.4 Deep Frozen Bank Bone 423

could, under sterile conditions, rinsed it with an antibi­otic solution, put it into a sterilized jar with a cover and then placed it into the deep freezer at at least 20° centi­grade below zero. In the same way we used surplus can­cellous bone or ribs we had taken from patients during surgery. Whenever there was need, we took it out of the deep freezer and implanted it sometimes more than two years after it had been taken. Today it is too risky to use deep frozen cadaver cancellous bone because of the possibility of various viral infections. One can obtain and use it only when that cadaver has been fully checked and approved as an organ provider.

Whether lyophylized bone is of any use for these pur­poses or not, I do not know. I can imagine that auto­claved bone could do very well for such purposes, as long as the gap is not more then 10 mm. It might be worthwhile to have it tested on animals first.