Minimally invasive orthognathic surgery: endoscopic vertical ramus osteotomy

Copyright © Munksgaard 2000

Int. J. Oral Maxillofac. Surg. 2000; 29:239-242 Printed in Denmark. All rights reserved

Maxillofacid Surgery I S S N 0901-502 7

Aesthetic and reconstructivesurgery

Minimally invasive orthognathic surgery: endoscopic vertical ramus

Maria J. Troulis 1, O d e d Nahlieli 2, Frank C a s t a n o 1, L e o n a r d B. Kaban 1 1Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston, Massachusetts, USA; 2Departmentof Oral and Maxillofacial Surgery, Barzilai Medical Center, Ashkelon, Israel

0ste0t0my M. J. Troulis, O. Nahlieli, F. Castano, L. B. Kaban. Minimally invasive orthognathic surgery: endoscopic vertical ramus osteotomy. Int. J. Oral Maxillofac. Surg. 2000; 29: 239-242. © Munksgaard, 2000 Abstract. The endoscopic procedure for placement and activation of a distraction device for mandibular advancement has been previously reported 2°. The purpose of this study was to demonstrate the feasibility of endoscopic exposure, dissection and osteotomy for mandibular set-back. Two cadaver and three anesthetized minipigs were used in this study. Access to the mandibular ramus was achieved through a 2.0 cm submandibular incision. The dissection was carried sharply to the mandible and completed in the subperiosteal plane. Visualization was achieved using a 2.7 mm diameter endoscope (Karl Storz, Germany). Landmarks were identified and a custom-made retractor was inserted into the sigmoid notch. A vertical ramus osteotomy was created (bilaterally) from the sigmoid notch to the mandibular angle. The mandible was set back (average 6 mm) and fixed using 2.0 mm diameter, bicortical screws. Live animals were sacrificed three weeks postoperatively. The mandibles were examined clinically and radiographically to verify proper osteotomy position and clinical union. In all animals, exposure, accurate identification of landmarks, osteotomy placement and screw fixation were achieved. In the live animals (n=3), union between the proximal and distal segments was documented by clinical and radiographic examination. This study demonstrates the feasibility of the EVRO procedure for mandibular set-back in a minipig model.

During the last 25 years there has been great interest in the development of minimally invasive techniques, initially for gynecologic1,4,21 and urologic surgery 1339, and subsequently for general 4'7&11, cardiovascular-', otolaryngologic3'~6'18 and facial esthetic surgery 1s,22. Recently, oral and maxillofacial surgeons have begun to develop endoscopic techniques for correction of facial soft tissue s and skeletal deformities 6'9'1°'17'20 and diseases of the salivary glands 12.

The benefits of endoscopy include small and remotely placed incisions, acceptable scars and direct visualization of an illuminated and magnified operative field. Minimal dissection and tissue manipulation result in decreased pain and swelling, less overall morbidity and faster recovery. For these reasons, minimally invasive surgery has gained enthusiastic public acceptance. Development and refinement of endoscopic techniques for exposure, creation of osteotomies and placement

Key words: ramus osteotomy; mandible; endoscopic; minimally invasive.

Accepted for publication 22 March 2000

of miniature buried distraction devices2° may, in the future, allow orthognathic procedures to be routinely performed under local anesthesia with intravenous sedation in an outpatient setting. This would have a significant impact on cost, patient morbidity and availability of treatment. The endoscopic procedure for placement and activation of a distraction device for mandibular advancement has been previously reported 2°. The purpose of this study was to demonstrate

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Fig. 1. Anesthetized, prepared and draped minipig with head in lateral position (right mandible). Surface landmarks: anterior and posterior borders of the mandible and the osteotomy (arrow) are outlined in Malachite green. Access to the mandible is gained through a 1.5-2 cm snbmandibular incision, directly in line with the proposed osteotomy.

the feasibility o f m i n i m a l l y invasive (endoscopic) exposure, dissection, vertical r a m u s o s t e o t o m y ( E V R O ) a n d rigid fixation for m a n d i b u l a r set-back. Material and methods Animals This study was performed in concordance with the regulations and approval of the In-

Fig. 3. (Right mandible) Endoscopic view showing the retractor (R) positioned in the sigmoid notch, condylar neck (C), and posterior border (P) of the mandible.

stitutional Animal Care and Use Committee (IACUC) of the Massachusetts General Hospital. The technique was initially developed using fresh cadaver heads stabilized on the operating table in the lateral position (n=2). Three live-anesthetized Yucatan minipigs were then used to test the technique in vivo. These animals were given sedation (Ketamine 20 mg/kg, IM) and transferred to the operating room for preoperative radiographs and photographs. A pulse oximeter was placed and general anesthesia was induced and maintained by mask inhalation (Isoflurane 1-2%). A peripheral intravenous catheter was inserted for antibiotics (Ancef 1

Fig. 2. Custom-designed retractor (R) is shown with a 2.7 mm, 30 degree Hopkin's T M endoscope (Karl Storz, Germany) inserted into a built-in channel and holder. The hook (h) at the most distal end of the retractor fits into the sigmoid notch. Long-handled, endoscopic elevators with a suction opening (arrow) in the blade (Snowden-Pencer, Tucker, GA) are used for the dissection.

Fig. 4. Endoscopic view of vertical ramus osteotomy (A, angle; S, sigmoid notch).

gm, IV) and maintenance parental fluid (lactated Ringer's 10 ml/kg/hr). The animals were prepared and draped in a sterile fashion to expose the right and left mandible.

Endoscopic technique Surface landmarks of the mandible were outlined in Malachite green. Access to the mandible was gained through a 1.5-2 cm submandibular incision, directly in line with the proposed osteotomy (Fig. 1). The dissection was carried sharply to the mandible and a subperiosteal pocket (optical cavity) was created with long-handled endoscopic elevators (Snowden-Pencer, Tucker, GA, USA) (Fig. 2). Then, a custom retractor and a 2.7 mm diameter endoscope (Storz, Germany) were placed through the port into the sigmoid notch. The posterior, superior, inferior and anterior borders of the mandible were identified (Fig. 3). Using a long-shank reciprocating saw (MicroAire, Charlottesville, VA, USA), the osteotomy was performed from the sigmoid notch to the mandibular angle (Fig. 4).

Fig. 5. Endoscopic view of completed osteotomy (O), towel clamp (T) engaging proximal fragment; distal segment (D).

Endoscopic ramus osteotomy

Fig. 6. Endoscopic view of the medial pterygoid muscle (M) being stripped from the proximal segment (P) with an endoscopic elevator (E). A towel clamp (T) placed on the proximal segment grasps and controls it.

Irrigation was accomplished through the endoscope. An osteotome was used to verify the completion of the osteotomy. A towel clamp was then placed to grasp and control the proximal fragment (Fig. 5). The medial pterygoid muscle was partially stripped to allow overlap of the distal and proximal segments (Fig. 6). Tile procedure was performed bilaterally. After placing the animal in maxillomandibular fixation, the mandible was set back (average of 6 mm). The proximal fragment was verified to be lateral to the distal and the segments were rigidly fixed using three or four 2.0 mm diameter, 14-16 mm long, bicortical screws (Synthes Maxillofacial, Paoli, PA, USA) (Fig. 7). The wounds were copiously irrigated with sterile saline and closed in layers using 34) chromic catgut sutures. Postoperative radiographs were taken, an Elizabethan collar placed and the animal returned to its cage. The pigs received a pureed diet ad libitum. The postoperative analgesic and antibiotic regimen consisted of Buprenorphine 0.3 mg IM and Fentanyl 25 #g/hr patch, and oral

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Fig, 7. Diagram (left) and endoscopic view (insert and right) of the set-back position, with overlap of the proximal (P) and distal (D) segments and three 2.0 mm diameter, bicortical screws (arrow).

Bactrim 800 mg b.i.d, for 7 days. Mean total operating time was approximately 2-3 hours versus 3045 minutes for the standard open technique in minipigs2°. Evaluation Immediately and three weeks postoperatively under anesthesia, the animals were examined to verify the stability of the postoperative occlusion. At 3 weeks, bimanual palpation was used to assess mandibular stability and clinical union across the osteotomies. Preoperatively, immediately and 3 weeks postoperatively, standard lateral cephalometric radiographs, with the head positioned in a custom cephalostat, were taken to verify jaw position. The animals were sacrificed after 3 weeks and the osteotomy sites examined to determine proper osteotomy orientation and clinical union.

Results In all animals (n=5, 2 cadavers and 3 live), exposure, accurate identification

of landmarks, osteotomy placement and screw fixation were achieved. In the three live animals, union between the proximal and distal segments was documented by clinical examination and jaw position by clinical examination and lateral cephalograms (Fig. 8).

Discussion The endoscopic procedure for placement and activation of a distraction device for mandibular advancement has been previously reported 14,2°. In this study we demonstrated the feasibility of minimally invasive (endoscopic) exposure, dissection, mandibular vertical ramus osteotomy (EVRO) and rigid fixation for mandibular set-back. Use of a small, extraoral submandibular incision minimizes dissection, bleeding and swelling. In addition, the approach allows the surgeon to visualize the operative field "en face", which

Fig. 8. A) Preoperative lateral cephalogram of minipig. All cephalograms were taken in a custom-made cephalostat. B) Postoperative lateral cephalogram showing the set-back position and screw fixation.

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is the most common and comfortable orientation. In contrast to reported intraoral endoscopic techniques, the extraoral approach allows the operator to place temporary wire maxillomandibular fixation while inserting plates and screws. This ensures accurate bone reduction and occlusion. Although the operating time for EVRO was significantly longer than open VRO in this model, we expect that this difference will greatly diminish with increasing operator experience. Even with longer operating times, in subsequent animal and patient experience, the postoperative pain and swelling was less and recovery quicker than with the open operation. Furthermore, rigid fixation is used so maxillomandibular immobilization is not necessary. In the long term, endoscopic techniques such as described in this study will be useful, in combination with three-dimensional computed tomographic. (3-D CT) treatment planning and surgical navigation systems for precise planning and execution of skeletal movements. The combination of new technologies (endoscopy, distraction osteogenesis, 3-D CT treatment planning and surgical navigation) may allow orthognathic surgery to be routinely and safely carried out in the outpatient setting with minimal patient morbidity and high patient acceptance. In addition, the EVRO, and other endoscopic procedures, may open the orthognathic surgery option for patients without third party insurance coverage. In this study we demonstrated the feasibility of the EVRO procedure for mandibular set-back in a minipig model. We predict that refinement of endoscopic techniques for human orthognathic surgery will allow oral and maxillofacial surgeons to routinely perform these procedures in an outpatient setting. Acknowledgments. This work was supported

by grants from the Center for Innovative Minimally Invasive Therapy, Massachusetts

General Hospital and the AO/ASIF Foundation, Davos Switzerland. Technical support was provided by Synthes Maxillofacial, Paoli, PA and Karl Storz, Germany. This work was presented in part at the 14th International Conference in Oral and Maxillofacial Surgery, Symposium on "Congenital and Developmental Craniomaxillofacial Disorders at the Millenium", Washington, D.C., April 1999.

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Address: Dr. Leonard B. Kaban Dept. Oral & Maxillofacial Surgery Massachusetts General Hospital Warren BmTding 1201 55 Fruit Street Boston, M A 02114 USA