Materials and Methods

Patients
In the past two years, we performed angle-splitting ostectomy on five Japanese patients over fifty years old (Table 1). All of the patients had this operation for a purely aesthetic purpose, and none had specific craniofacial anomalies. Three of them had operation of rhytidectomy several months later. None had simultaneous ostectomy and rhitidectomy. We found no particular risks for general anesthesia in these patients in preoperative examinations, and all cases underwent surgery under general anesthesia. We routinely suggested patients to give 400 ml of their own blood at the time of preoperative examinations for auto-transfusion, and four of five patients did so.

Operative Procedures
The operations were performed mostly according to previous publications by Deguchi et al.2 and Han and Kim3, with slight modifications. In brief, the oral mucosa was incised along the mandibular ramus, from the point just beside the parotid papilla to the first molar. The lateral surface of the mandibular angle was exposed by subperiosteal dissection. The caudal end of the masseter muscle was carefully released from the mandible, but we did not cut or resect the muscle berry. A deep groove was hollowed out on the lateral cortex using a round burr, along the upper and anterior boundary of the ostectomized area (Fig. 1A). Several perforations were made using a Lindemann drill burr (Downs Surgical, Sheffield, UK) from this groove toward the posterior and inferior margin of the mandible, in parallel with and just under the lateral cortex, to avoid any unexpected malfracture (Fig. 1B). Then, the lateral cortex of the angular bone was ostectomized with a bone chisel. If necessary, the tip of the angle can be additionally excised with an oscillating saw (Fig. 1C). The released end of the masseter muscle was left detached. Finally, a Penrose drain was inserted, the oral mucosa was closed with absorbable 4-0 sutures, and a pressure mask was applied and left overnight. The Penrose drains were removed a few days later.

Results
The splitting-angle ostectomy was performed successfully in all cases. Avarage operation time was 2 hours and 50 minutes. Average amount of hemorrhage was 500 ml, and the four patients who gave their own blood preoperatively, underwent auto-transfusion just before finishing surgery. No patients required blood transfusions from other persons. No malfractures of the mandible body, ramus or condyle occurred. The right inferior alveolar nerve was unexpectedly damaged during the splitting ostectomy in one patient (Case 5). In this case, the ramus was atrophic, possibly due to previous extraction of the molars and premolars. The nerve was repaired with 8-0 nylon sutures and fibrin glue.
Postoperative recovery of general conditions was uneventful, and no patients exhibited circulatory or respiratory problems. No hematomas or no local infections were observed. Transient unilateral sensory disturbance of the skin in the mental nerve area was observed in two cases (in addition to Case 5), and slight paralysis of the marginal mandibular branch of the facial nerve was seen for a few days in one case. Aesthetic outcomes were quite satisfactory in all cases. Skeletal contours of the lower face were significantly changed. Effects of the facelift were remarkable in the three patients who underwent subsequent rhytidectomy.

Case 1
A 55-year-old woman sought treatment for prominent mandibular angle (Figs. 2A and 2D). She had a constant complaint about the shape of her mandible from her teenage. Also she wished to undergo a face-lift. She had no special history of past illness. X-rays and 3D-CTs showed remarkable protrusion and lateral flaring of the mandibular angle (Figs. 2G and 2I). The angle-splitting ostectomy was performed under the general anesthesia, and 5 x 2.5 cm fragments of the lateral cortex were removed bilaterally. Postoperative X-rays and 3D-CTs showed significant reduction of the lateral cortex (Figs. 2H and 2J), and her facial contour was remarkably changed two months after the ostectomy (Figs. 2B and 2E).
A rhytidectomy with radical SMAS lift was performed three months after the ostectomy. The lifting was very effective for reducing redundancy of the skin in the mandibular area (Figs. 2C and 2F). No specific problem was observed except slight and transient sensory disturbance in her left lower lip. The patient was very satisfied with the final result.

Case 2
A 65-year-old woman was referred to us for treatment for her facial contour (Fig. 3A). She had been unhappy with her angled face and low nose since childhood. She had a history of asthma, but no attacks in the last 10 years. A preoperative spirogram showed no problems, and she underwent angle-splitting ostectomy under general anesthesia. The angled contour was improved, but the upper part of the angle was not completely resected (Fig 3b). Seven months later, we performed a correction of mandibular angle--through a facelift incision with great care not to damage the submandibular branch of the facial nerve-- together with an SMAS facelift and insertion of silicone implants into her nasal dorsum. The final result was very satisfactory (Fig.3C).

Case 3
A 51-year-old housewife had a complaint about her prominent zygoma and mandible (Figs. 4A and 4C). She underwent a resection of the uterus myoma several years ago, but had no other particular history. In this case, the lateral flaring was not so remarkable, but the whole mandibular angle was hypertrophic in the preoperative 3D-CT (Fig. 4E). She underwent angle-splitting ostectomy under general anesthesia. Postoperative recovery was uneventful. A SMAS lift was performed five months later, and the postoperative contour was markedly improved (Figs. 4B, 4D and 4F).

Discussion
There have been a number of reports on surgical methods for angular faces. This condition was historically called "benign masseteric hypertrophy", and resection of the masseter muscle as well as bone was originally regarded as essential5,6. However, angled appearance of the face in Orientals can be primarily attributed to a lateral flaring of the bony angle7. The masseter muscle, which always exhibits tetanic contration, as do the calf muscles, can be atrophied only by releasing the end of the muscle3, and also by inducing temporal paralysis with Botulinus toxin8. Therefore, the mandibular angle ostectomy without muscle reduction can be a primary procedure sufficient for this condition. Some authors reported a simple full-thickness excision of the protruding part of the bony angle1,7,9, which may often be accompanied by an unnecessary change of SN/MP angle. Therefore, a lateral cortical reduction by angle-splitting ostectomy is now the first choice of operative options for the majority of patients2,3.
In this paper, we described our experience of the angle-spliting ostectomy in five aged Japanese women. Most of the operative procedures are the same as in younger patients, and the aesthetic results were quite satisfactory. The final results were most dramatic when the ostectomy was combined with subsequent rhytidectomy, as seen in Cases 1, 2 and 3. It has been pointed out that rhytidectomy in Asians requires special considerations, because the facial skeletal contour in Orientals is round and squared as Shirakabe et al. described in the "baby model" paradigm4,10. Oriental skin is thicker than that of Caucasians with abundant extracellular matrices10, and this fact also contributes to the difficulty of Asian rhytidectomy. In this sense, after correcting angular skeletal contours with angle-splitting ostectomy, facelift can be performed more easily in Orientals with ideal clinical results. Baek et al.7 also reported a combination of angle ostectomy and rhytidectomy in several patients, the two procedures performed simultaneously in their cases. However, we prefer two-stage operations with an interval of several months for the following reasons. One reason is to avoid lengthy operation time, considering that Orientals need vigorous SMAS lift as noted above. Delicate adjustment of the bony angle shape can be achieved in the second operation through a facelift incision as seen in Case 2--another advantage of our two-stage strategy. We consider the most important reason to be that sufficient lifting is likely impossible in the one stage operation due to intraoperative swelling caused by the ostectomy.
Several problems should be borne in mind when the angle-splitting ostectomy is performed on the elderly. Most important is atrophy of the mandible, as seen in Case 5. In this case, the inferior alveolar nerve was damaged during the splitting ostectomy partly due to the thinness of the bony angle. As stated by Moss and Salentijn11 in their "functional matrix" concept, craniofacial bone remodeling is mainly controlled by external mechanical stresses. The edentulous mandible in the elderly often exhibits remarkable atrophy mainly in the alveolus by the loss of stress through the teeth12. In Case 5, the bilateral molars and premolars were missing and the 3D-CT revealed atrophy and thinness around the mandibular angle (Figs. 5A and 5B). However, we can also detect in this CT a remarkable lateral flaring of the angle, which causes a prominent mandibular angle (Figs. 5B and 5C). The mechanisms by which the functional matrix works are completely different between the alveolus and the lateral flaring of the angle, because the bone deposition in the lateral cortex of the mandibular angle is considered to be affected by the tention of the masseter muscle13. This is the reason why a prominent mandibular angle can be observed even in the edentulous atrophic mandible. We can treat such cases with reduction mandibuloplasty, but special care should be taken not to damage the inferior alveolar nerve and to avoid malfractures. It is reported that the mandibular canal remains intact around the angle even in the completely edentulous mandible12, and this fact supports our opinion that angle-splitting can be safely performed if the surgeons are well acquainted with the specific features of mandibular atrophy in elderly patients. Preoperative 3D-CTs may be quite informative for this purpose.
Other risks of the angle-splitting ostectomy include hemorrhage from branches of the facial artery. We encountered a relatively large amount of hemorrhage in three patients. This risk can be minimized by preparation of the auto-blood transfusion. Collaboration with anesthesiologists is also essential for avoiding general risks potentially serious in the elderly, and with their help we did not experience any circulatory or respiratory troubles pre- or post-operatively.
In conclusion, we believe the angle-splitting ostectomy for the prominent mandibular angles can be safely and effectively performed on elderly patients, if the surgeon is well acquainted with the specific features in elderly cases, and a multi-disciplinary support system is available.

Legends


Fig.1 Illustrations of the operative procedures. (A) A deep groove is made along the shaded area (upper and anterior boundary of the ostectomy), using a round burr. (B) Several perforations are made using a Lindemann drill burr from this groove in various directions (arrows). (C) The lateral cortex of the angular bone is ostectomized with a bone chisel. The tip of the angle is additionally excised with an oscillating saw, if necessary.

Fig.2 Case 1. A 55-year-old woman. (A, D) Preoperative appearance. (B, E) Two months after the ostectomy. (C, F) Two months after the SMAS lift. (G) Preoperative frontal cephalogram shows remarkable lateral flaring of the mandibular angle. (H) Post-ostectomy cepharogram. (I) Preoperative 3D-CT. (J) Post-ostectomy 3D-CT reveals a successful reduction of the angle.

Fig.3 Case 2. A 65-year-old woman. (A) Preoperative appearance. (B) Appearance after the angle-splitting ostectomy. Some protrusion is left in the angle. (C) Final appearance, 1 year after the ostectomy and five months after the SMAS lift. The angle shape was adjusted through the facelift incision. She also underwent augmentation of the nose at the secondary operation.

Fig.4 Case 3. A 51-year-old woman. (A,C) Preoeprative appearance. (B, D) Postoperative appearance, 8 months after the ostectomy and three months after the SMAS lift. (E) Preoperative 3D-CT reveals remarkably hypertrophic angle of the mandible. (F) Postoperative 3D-CT shows that the ostectomy was effective.

Fig.5 Preoperative CT of the edentulous mandible of Case 5, a 69-year-old woman. (A) CT of the oblique plane of the left mandibular angle. Note the lateral flaring of the angle (arrowhead) even though the mandibular body shows remarkable atrophy (arrows) due to the extraction of the molars and premolars. (B) A caudal view of the mandible by 3D-CT shows atrophy around the angle (arrows). (C) A lateral view of the mandibular angle by 3D-CT. The lateral flaring is obviously noted (arrowhead).

Table 1. Patient Profiles
Case
number age sex operation time bleeding (ml) auto-blood transfusion intraoperative
nerve injury subsequent
face lift follow
-up
1 55 F 2h25m 400 + - + 1y11m
2 65 F 1h55m 100 - - + 1y2m
3 51 F 2h15m 560 + - + 8m
4 61 F 3h00m 670 + - - 6m
5 69 F 4h20m 770 + + - 3m

References

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