J Oral Maxillofac Surg59:15-18, 2001

Minimizing Displacement of the ProximalSegment After Bilateral Sagittal Split

Ramus Osteotomy in Asymmetric CasesKenji Yoshida, DDS, PhD,* Rosario S. Rivera, DDS,†

Michio Kaneko, DDS, PhD,‡ and Kenichi Kurita, DDS, PhD§

Purpose: This study evaluated a modified sagittal split ramus osteotomy designed to minimize dis-placement of the proximal segmentation asymmetric cases.

Patients and Methods: Nine patients with facial asymmetry were corrected with modified bilateralsagittal split ramus osteotomy from November 1992 to February 1999. Preoperative and 3-monthpostoperative anteroposterior (AP) radiographs were traced and compared. The angle of mandibularrotation of the proximal segments was obtained by measuring the intersection of lines passing throughthe upper rim of the orbit and the lateral border of the proximal segment. The condition of thetemporomandibular joint (TMJ) was evaluated clinically by measuring the interincisal distance andlooking for any untoward symptoms.

Results: The data showed an average 1.94° � 1.18° difference between the preoperative and postop-erative condition and no clinical signs of TMJ symptoms. These findings support the use of this procedurefor treating asymmetric mandibles.© 2001 American Association of Oral and Maxillofacial Surgeons

One of the most difficult dentofacial deformities tocorrect is facial asymmetry. Several factors shouldbe considered when developing the treatment plan.Aside from aesthetic considerations, stability of theosteotomized segments also should be a part of theprimary concern in performing the operation.There is a tendency for the proximal segment to bedisplaced during transoral vertical osteotomies, andthe displacement is greater in sagittal osteotomies.1

The degree of proximal segment rotation duringsurgery, whether forward or backward, is associ-ated with short-term instability.2 Moreover, changein condylar position is one of the most commonreasons for the short-term relapse of orthognathic

surgery cases.3 Consequently, we developed a mod-ified sagittal split osteotomy to minimize postoper-ative displacement.4

Because of proximal segment displacement duringbilateral sagittal split osteotomy with either setback oradvancement, we have modified the surgical proce-dure for the treatment of asymmetric cases. Based onour clinical experience, shifting the mandible, specif-ically the distal segment, more than 5 mm whencorrecting an asymmetric case has a detrimental ef-fect on the position of the proximal segment. Rotat-ing the distal segment toward the long side more than5 mm will displace the proximal segment on the shortside (Fig 1). To prevent proximal segment malposi-tion, the osteotomy on the distal segment on the shortside is modified. On the long side, a conventionalosteotomy is performed.

Surgical Technique

The conventional mucosal incision is made overthe external oblique ridge, extending halfway fromthe ramus to the first molar area. This is followed byelevation of the soft tissues and muscle attachmentsto provide adequate exposure. Usually, the lingualosteotomy is made horizontally above the lingula, butin these cases, because the distal segment on theshort side has to be shifted more than 5 mm, theosteotomy is angled downward (Fig 2). The buccal

Received from the First Department of Oral and Maxillofacial Sur-

gery, Aichi-Gakuin University, School of Dentistry, Nagoya, Japan.

*Associate Professor.

†Visiting Researcher from the University of the East, Philippines.

‡Assistant Professor.

§Professor.

Address correspondence and reprint requests to Dr Yoshida:

First Department of Oral and Maxillofacial Surgery, Aichi-Gakuin

University School of Dentistry, 2-11 Suemoridori, Chikusa-ku,

Nagoya 464-8651 Japan; e-mail: kenji@dpc.aichi-gakuin.ac.jp

© 2001 American Association of Oral and Maxillofacial Surgeons

0278-2391/01/5901-0004$3.00/0

doi:10.1053/joms.2001.19264

15

osteotomy is made horizontally below the lingual os-teotomy. The angulation of the lingual osteotomymakes the posterior aspect of the distal segmentshorter, thereby preventing overlap of the 2 segmentsduring fixation. Figure 3 shows the triangular spacecreated by angulation of the lingual osteotomy. Thisspace is a crucial part of the procedure, which pro-vides a noncontacting surface when the 2 segmentsare fixed. Temporary maxillomandibular fixation isperformed by using an acrylic splint to determine thecorrect occlusion, followed by fixation of the proxi-mal and distal segments (Fig 3). During osteosynthe-sis, the gap is maintained by the surgeon holding theanterior part of the proximal segment with a bone

forcep. The correct position of the condyle is thenchecked by manual manipulation. Finally, suturing iscompleted, and maxillomandibular fixation (MMF) isreapplied.

Subjects and Methods

Nine patients with asymmetric mandibles under-went bilateral sagittal split ramus osteotomy fromNovember 1992 to February 1999. The maximumfollow-up period was 5 years. All cases were cor-rected by using the modified technique for the shortside. Anteroposterior (AP) radiographs taken preop-eratively and 3 months postoperatively were used todetermine any changes in the position of the condyle.The amount of displacement of the proximal segment

FIGURE 1. Diagrams showing effect of mandibular asymmetry oncondylar position. A, Example of an asymmetric case. B, In correctingasymmetric cases with the conventional sagittal split ramus osteotomy,the condyle on the short side rotates as the distal segment pushes theproximal segment. (Reprinted with permission.4)

FIGURE 2. Diagram of the downward angulation of the lingualosteotomy (A: dotted line), making the posterior aspect of the distalsegment shorter than with the conventional osteotomy. Buccal osteot-omy line (B: solid line).

FIGURE 3. Triangular space created by angulating the lingual os-teotomy downward on the short side to prevent overlapping of thebony segments during fixation. (Reprinted with permission.4)

16 MINIMIZING DISPLACEMENT OF THE PROXIMAL SEGMENT

was determined by measuring the angle of mandibu-lar rotation on tracings made from the AP radio-graphs. Lines passing through the upper rim of theorbit and the lateral border of the proximal segmentwere used, and the angle of intersection of these 2lines was measured (Fig 4).

Clinical examination of the temporomandibularjoint (TMJ) was also done. Maximum mouth openingwas measured starting from the release of the MMF,which was approximately 5 weeks after the opera-tion. Development of TMJ symptoms was routinelyrecorded.

Results

In 5 cases, the short side was modified and fixedwith miniplates placed on the external oblique ridge,and the other side was fixed with wire. The remaining4 cases were fixed using only wire.

Measurement of the amount of proximal segmentdisplacement on the short side showed an average1.94° � SD 1.18° difference between preoperative

Table 1. PREOPERATIVE AND POSTOPERATIVEMEASUREMENTS OF THE POSITION OF THEPROXIMAL SEGMENT (SHORT SIDE)

Patients FixationPreoperative

AnglePostoperative

Angle Difference

A Plate and wire 84.0° 81.0° 3.0°B Plate and wire 87.0° 84.5° 2.5°C Wire 87.0° 84.0° 3.0°D Wire 88.0° 90.0° 2.0°E Wire 87.5° 83.0° 3.5°F Plate and wire 81.0° 79.0° 2.0°G Wire 81.0° 80.5° 0.5°H Plate and wire 84.0° 83.5° 0.5°I Plate and wire 82.5° 82.0° 0.5°

NOTE. Average � 1.94° � SD 1.18°.

FIGURE 5. Comparison of the radiographs of the condyle in case F.A, Preoperative; B, immediate postoperative; C, 5 years’ follow-up.Note the relatively unchanged position of the condyle.

FIGURE 4. Angular measurements of the proximal segment position.

YOSHIDA ET AL 17

and postoperative condition (Table 1). Only 1 of the9 cases showed an increase in the postoperative an-gle, whereas the remaining 8 showed a decrease. Thelargest angle measured was 3.5°, and the smallestangle was 0.5°. Postoperative radiographs showed noabnormal position of the condyle (Fig 5). Further-more, no patients complained of any postoperativeTMJ symptoms during the follow-up period, whichranged from 2 years 6 months to 5 years. It wasconcluded that any discrepancy in condylar positionproduced was within the range of tolerable condylarrotation, with no detrimental effects on stability orevidence of any TMJ symptoms.

Discussion

Change in condylar position is very common duringorthognathic surgery. Avoiding this change is crucial tothe stability of the operation as well as in the avoidanceof TMJ symptoms. Establishing the exact angulation foreach case preoperatively is impossible, but this can beresolved during surgery by determining the position ofthe condyle by using clinical judgment.

The modification presented was effective in themanagement of facial asymmetries and avoided dis-

placement of the proximal segment. Because the areaof bone contact produced by this procedure is nar-row, it may result in nonunion between the proximaland distal segments. When the osteosynthesis materi-als were removed after 1 year in 4 cases, the healingbetween the segments could be clearly determined bydirect observation. No differences in plate or wirefixation were observed, but confirmation as towhether all cases resulted in healing without non-union was not undertaken. Moreover, the effect whenhaving 2-jaw surgery was not considered. Therefore,we recommend further study before a wider applica-tion of this technique.

References1. Tucker MR, Terry BC, White RP Jr, et al: Rigid Fixation for

Maxillofacial Surgery. Philadelphia, PA, Lippincott, 1991, p 2652. Ellis E III: Condylar positioning devices for orthognathic surgery:

Are they necessary? J Oral Maxillofac Surg 52:536, 19943. Rotskoff KS, Herbosa EG, Villa P: Maintenance of condyle-prox-

imal segment position in orthognathic surgery. J Oral MaxillofacSurg 49:2, 1991

4. Fukaya M, Kaneko M, Yoshida K: Surgical treatment of mandib-ular asymmetric cases (in Japanese). Jpn J Jaw Deform 3:99,1993

18 MINIMIZING DISPLACEMENT OF THE PROXIMAL SEGMENT