J Oral Maxillofac 54:45-53, 1996
Surg
Distraction Osteogenesis in Maxillofacial Surgery Using In ternal Devices: Review MARTIN
CHIN,
of Five Cases
DDS,” AND
BRYANT
A. TOTH,
MDT
Purpose: The purpose of this report is to show the feasibility and potential advantages of using internal devices for distraction osteogenesis in the management of maxillofacial skeletal deficiencies. Patients and Methods: Distraction osteogenesis was used to correct a variety of maxillofacial skeletal deformities in five patients. One patient underwent bilateral Le Fort III advancement aided by distraction, three patients underwent mandibular ramus lengthening, and one patient underwent segmental alveolar reconstruction by distraction. The devices were activated by either a transcutaneous or transmucosal pin. After achievement of the desired skeletal transport, the activating pins were disengaged and removed from the distraction device. This allowed the distraction device to remain submerged and to stabilize the site of the consolidating bone. Results: All patients achieved lengthening of their jaws. However, premature consolidation was noted in two patients, and one patient had significant relapse. Conc/usions: Development of internal distraction devices is important to address the limitations of currently available biphasic systems. Potential benefits of internal devices include 1) elimination of skin scarring caused by translation of transcutaneous fixation pins, 2) improved patient compliance during the fixation or consolidation phase because there is no external component, and 3) improved stability of the attachment of the device to the bone.
Ilizarov’ is credited with defining the biologic basis and establishing an armamentium to allow practical, clinical use of skeletal distraction to regenerate bone for management of a variety of limb deformities. Early clinical applications of distraction osteogenesis for the correction of maxillofacial deformities have relied on orthopedic devices to achieve transport and fixation of the bone. McCarthy et al2 reported use of a miniaturized Hoffman device to lengthen human mandibles. Tschakaloff et al” described a technique to internalize a distraction transport system for experimental manip-
ulation of calvarial sutures in rabbits. Practical application of this technology to pediatric maxillofacial surgery requires modification of the orthopedic armamentarium, surgical technique, and distraction protocol to address the special features of the pediatric facial skeleton and special management needs of the child. Patients
Five patients underwent distraction osteogenesis. Two of the patients underwent bilateral distraction. Ages ranged from 2 to 17 years. Each patient had a custom distraction device fabricated. Articulated dental models, dental radiographs, three-dimensional computed tomography (CT) images, and milled skeletal models from CT data were used to plan the surgery and fabricate the distracters. The design of each distractor was determined by 1) the desired vector and magnitude of skeletal correction, 2) dysmorphology of
Received from California Pacific Medical Center, San Francisco, CA. * In private Practice, Oral and Maxiilofacial Surgery. t In private Practice, Plastic and Reconstructive Surgery. Address correspondence and reprint requests to Dr Chin: 2100 Webster St, Suite 303, San Francisco, CA 94115. 0 1996 American
Association
of Oral and Maxillofacial
and Methods
Surgeons
0278-2391/96/5401-0009$3.00/O
45
46
DISTRACTION
OSTEOGENESIS
FIGURE 1. 2 $-year-old boy with right craniofacial microsomia. A, Preoperative deficiency of right facial contour. B, CT three-dimensional reformation showing cant of mandible. C, CT three-dimensional reformation showing absence of glenoid fossa. D, CT model used as template to fabricate distractor. E, Distractor in place before mucosal closure. F, Distractor in place, activation pin removed, device submerged. G, Distractor extended at time of removal. H, Postdistraction improvement in facial contour.
the distraction site, 3) access for placement of the device and osteotomy, 4) access for the placement of the activating pin, and 5) anticipated patient cooperation with the device activation process. The distraction devices consisted of bone plates fabricated to engage threaded K-wires. When the threaded rod was turned, the attached bone plates separated. The skeletal fragments were transported with the attached
plates. One patient required incorporation of a rightangled gearbox mechanism to allow transoral access for activation. All devices were stabilized to the skeletal fragments with 2-mm diameter self-tapping screws. All of the devices for mandibular distraction were placed transorally. Two patients had transmucosal activating pins that were activated by a key introduced through the mouth. Two patients had transcutaneous
CHIN
AND
TOTH
47
48
FIGURE 2. 12-year-old boy with Pfeiffer syndrome. A, Preoperative facial profile showing midface retrusion. B, Preoperative lateral cephalometric radiograph showing Class III relationship. C, Distraction bone plates for right and left zygoma. D, Distraction bone plate in placed, left zygoma.
pins with removable, external knobs. The patient undergoing Le Fort III advancement by distraction had bilateral distracters placed via the coronal access used to perform the osteotomies. Bilateral, transcutaneous pins were used to activate the Le Fort III distracters. Both the transcutaneous and transmucosal activating pins were locked into the distracters in such a manner that they could be disengaged and removed after the
DISTRACTION
OSTEOGENESIS
CHIN
AND
TOTH
FIGURE 2. (Conr’d). E, Submentovertex radiograph showing orientation of distracters. F, Transcutaneous activation pin being removed. G, Postoperative facial profile showing improved convexity. H, Postoperative lateral cephalometric radiograph showing improved facial proportions.
completion of skeletal transport. The mandibular osteotomies were all performed by a transoral approach. The latency period, the delay between the osteotomy and onset of distraction, ranged from 0 to 5 days. The rate of distraction varied from 1 to 3 mm per day. The amount of immediate distraction, the separation of the osteotomy at the time the device is placed, ranged from 4 to 12 mm. Results All patients achieved clinical lengthening of their skeletal deformities. One patient experienced significant relapse of mandibular lengthening. In two cases, the distraction sites were reentered after 5 months to recover the distraction devices. In both of these cases, examination showed the distraction sites to be well consolidated and that the distraction devices remained fixed to the bone. Two patients had premature consolidation of the distraction sites. One patient with premature consolidation required surgery to mobilize the distraction site to complete the distraction. Another patient, undergoing bilateral mandibular distraction,
had an expansion screw break and required replace the component.
surgery
to
Report of Cases Case I A 2’/,-year-old boy with right craniofacial microsomia (Fig 1A) underwentosteotomy and placement of an internal distraction device with a transcutaneous activating pin. A CT scan with three-dimensional reformation demonstrated the extent of the deformity and absence of the right glenoid fossa (Fig lB, C). CT data were inputted into a CNC (computer numeric control) milling machine to produce a mandibular replica. The replica was used in the model surgery and to fabricate the distraction device (Fig 1D). The osteotomy and placement of the distraction device were performed through a mucosal incision such as used in sagittal split osteotomies. The osteotomy was mobilized and distracted by 4 mm at the time of surgery. The distraction device was placed on a subperiosteal plane and fixed to the mandibular fragments with 2-mm cortex screws (Fig IE). After a 5-day latency period, distraction was begun and proceeded at 0.25 mm, four times a day. The device was activated by a transcutaneous submandibular pin. After 7 days, the distractor encountered resistance, and the further transport could not be achieved. The patient was returned to the operating room,
50 where examination showed a dense, noncompliant tissue mass adjacent to the lingual periosteum. An osteotome was used to divide the tissue, and it was confirmed that the device was able to distract the segments further. After a total of 17 mm of distraction was achieved, the transcutaneous pin was removed (Fig lF), and the skin penetration site was allowed to heal. Five months after the initial procedure, the patient was returned to the operating room for removal of the distractor. The bone filling the distraction site was firm and stable (Fig 1G). The morphology of the bone followed the contour of the distractor. The width of the newly formed bone was greater than the native ends. There was no evidence that the subperiosteal presence of the distractor hindered bone formation. Lengthening of the mandibular ramus resulted in an improvement in the facial contour (Fig 1H). Case 2 A lZyear-old boy with Pfeiffer’s syndrome had severe midface hypoplasia involving the orbits, zygoma, and maxilla. At the age of 7 years, he underwent orbitocranial reconstruction with advancement of the supraorbital bar and frontal bones. The current procedure involved a Le Fort III osteotomy with advancement assisted by distraction. Figure 2A and B shows the preoperative facial profile and radiograph. The zygoma, inferior orbits, and nasomaxillary complex were mobilized as a single unit, and the midface was advanced 10 mm during surgery. Distracters were then fixed to the osteotomy sites in the malar regions using 2-mm cortex screws (Fig 2C, D, E). For activation, each distractor incorporated a transcutaneous pin that emerged in the infraorbital region (Fig 2F). Postoperatively, the distracters were activated 0.5 mm four to six times per day; no latency period was observed. After 5 days, the right distractor had moved 9 mm and the left 11 mm. The difference in right versus left distraction allowed correction of an asymmetry in the maxillary dental midline. The postoperative photograph and lateral cephalometric radiograph demonstrate the improved relationship between the midface, mandible, and cranium (Fig 2G, H). The combination of intraoperative movement and postoperative distraction translated the midface 19 and 21 mm on the right and left, respectively. On the fifth postoperative day, the transcutaneous pins were disengaged, and the patient was discharged.
DISTRACTION
OSTEOGENESIS
lus, lower incisors, and overlying mucosa had been avulsed. The result was a residual alveolus lacking in width and height (Fig 4A). There was also a deficiency in mucosa. The prosthodontist requested placement of two osseointegrated implants. Orthodontic treatment had closed the edentulous space to accommodate the width of two incisors. The deficiency in the edentulous ridge made ideal implant placement impossible without reconstructing the site or compromising the periodontal health of the adjacent teeth. The treatment plan involved transporting a segment of alveolus vertically into the deficient area. The superior, knife-edge ridge was resected and a segmental osteotomy created a block of alveolus for vertical transport (Fig 4B). A threaded pin was used to fix the fragment, and a threaded bone plate was used as anchorage for the pin (Fig 4C). A latency period of 5 days was observed. The distraction then proceeded at 1 mm per day for 9 days. The pin was then left in place for 10 days without activation, at which time it was unscrewed and removed. There was a marked improvement in the width and height of the alveolus (Fig 4D, E). The site was reentered after 6 weeks to recover the anchoring plate and to place osseointegrated implants. At the time of reentry, the segment was clinically stable (Fig 4F) and the increased bone mass made the site suitable for placement of endosseous implants. Case 5 A 4-year-old girl with Goldenhar syndrome underwent distraction osteogenesis of the left mandible. The child had a canted occlusal plane typical of primary ramus hypoplasia. Figure 5A shows the preoperative view of the patient. The facial contour has been overcorrected, with the chin deviating to the right side. The surgical procedure involved a modified sagittal split performed on the left ramus. The mandibular nerve was isolated as it entered the mandibular foramen. A horizontal osteotomy was placed through the medial cortex above the foramen. A second, parallel osteotomy was placed through the lateral cortex of the ramus approximately 10 mm inferior to the previous osteotomy. A short, vertical osteotomy along the anterior border of the ramus then connected the two horizontal cuts. A periosteal elevator was used to separate the osteotomy. The result was a sagittal osteotomy with only 10 mm of overlap. The osteotomy site was displaced and
Case 3 A 5-year-old boy with micrognathia, mandibular arthrogryposis, and an open bite underwent bilateral distraction of the mandibular rami. Oblique osteotomies were performed through the mandibular angles, and bilateral distracters were placed. Each distractor was activated by a transcutaneous submandibular pin. Marked resistence to mandibular advancement was noted at the time of distractor placement. No latency period was observed. The pins were activated 0.5 mm four times a day or 2 mm per day. Figure 3 shows the distraction devices in the extended position. After achieving 10 mm for transport, the right distractor fractured. The patient was returned to surgery to replace the broken component. The d&actors were activated to a total transport of 18 mm, after which they were disengaged. Postoperative cephalometric radiographs showed significant relapse in the correction. Case 4 A 17-year-old girl was involved in an automobile accident when she was 14 years old. The anterior mandibular alveo-
FIGURE 3. Panorex of a 5-year-old boy with micrognathia showing bilateral distraction devices in extended position. The transcutaneous activation keys have been removed.
CHIN AND TOTH
5-l
FIGURE 4. 17-year-old girl with traumatic defect of alveolus. A, Preoperative view of alveolar ridge showing width deficiency. B, Preparation of mandibular segment for vertical transport. Note superior aspect of the ridge is to be resected. C, Transmucosal screw for transport of the fragment. D, Postdistraction alveolar ridge showing improvement in width. E, Postdistraction alveolar ridge showing improvement in height. F, Alveolar ridge width at the time of osseointegrated implant placement. the distraction device positioned and fixed with 2-mm selftapping screws. The design of the device incorporated three telescopic components that could be activated independently (Fig 5B). At the time of surgery, two of the telescopes were activated to achieve an intraoperative ramus lengthening of 12 mm (Fig 5C). The third expansion compon&t was-reserved for postoperative distraction and could be periodicallv activated by a ‘transmucosal key. The activating rod was positioned through the mucosal incision, adjacent to the posterior molar (Fig 5D). A latency period of 5 days was ob-
served. Distraction then proceeded at 0.5 mm two to four times a day. By the 14th postoperative day, the total distraction had reached 25 mm, and the transmucosal pin was removed. Figures 5E and F shows the final result.
Discussion McCarthy et al2 and others4,5 have demonstrated the of using distraction osteogenesis to correct
feasibility
DISTRACTION
FIGURE 5. A 4-year-old girl with Goldenhar syndrome. and activation. C, Distractor at time of placement, prior Postoperative improvement in facial contour. F, Posterior
OSTEOGENESIS
A, Preoperative deficiency of left facial contour. B, Distractor for transoral placement to mucosal closure. D, Appearance of removable, transmucosal activation port. E, open bite as a result of vertical ramus lengthening.
mandibular deficiencies. External distraction hardware anchored by transcutaneous pins was used to achieve transport and stabilization of the skeletal fragments. Development of internal distraction devices is necessary to make the treatment acceptable in the mainstream practice of pediatric maxillofacial surgery. The cases presented demonstrate that internal devices can be used to manage a variety of skeletal deficiencies.
Internalization of distraction hardware also allows application of the technology to a wide range of anatomic locations. Because the devices were designed to be submerged, they provided internal fixation that usually does not require maintenance. Newly formed bone is supported by the distraction device, which serves as a bone plate in the fixation phase of treatment. Because the devices were placed by a transoral approach, there
CHIN
AND
TOTH
are no skin incisions and limited risk to the branches of the facial nerve. Movement of large skeletal fragments, such as in Le Fort III advancements, typically require overcoming major resistance from the soft tissue envelope. Incremental movement using distraction mechanics allows displacement of fragments over large distances because the soft tissue is allowed to accommodate slowly. By combining the conventional Le Fort III osteotomy with postoperative gradual distraction, a correction of 20 mm was achieved in case 2. In addition, the axis of correction and method of fixation were controlled by the distraction device. The results of these early cases raise a number of questions that will need to be addressed by long-term follow-up and careful study of future cases. Protocols accepted in adult orthopedic distraction osteogenesis may not be directly applicable to pediatric maxillofacial surgery. The rate of distraction and length of latency before the onset of distraction need further study. There is a clear risk of premature consolidation of the osteotomy site if the rate of distraction is too slow. If the parents have difficulty activating the device or if the latency period is too long, premature consolidation may also occur. This complication is of particular concern in very young patients who seem to consolidate very rapidly at the distraction sites. Because of these concerns, we have modified the surgical technique and distraction protocol. Our procedure for mandibular lengthening by distraction is as follows: The osteotomy involves isolation of the neurovascular bundle so it is tethered by only the distal fragment. This is done by performing a modified sagittal split osteotomy. Isolation of the neurovascular bundle allows major displacement of the osteotomy at the time of surgery. Access while performing the modified sag&al osteotomy allows for direct visualization and protection of both the lingual and inferior alveolar nerves. Displacement of the fragments before placement of the distraction device results in an increase in the magnitude of distraction in a short period.
53
In addition, the axis of displacement before placement of the distractor may be different from the axis achieved by the distractor. The combined movement may produce an improvement in anatomic correction, but it requires careful planning. The long-term effect of early skeletal correction with distraction osteogenesis is unclear. Further study is required to evaluate the potential of early surgery to limit compensatory growth abnormalities. One of the current challenges is to determine how best to achieve a stable neuromuscular matrix to support the reconstructed skeleton. Patients with mandibular arthrogrypotic features are particularly challenging from this standpoint. Combining distraction with preoperative muscular conditioning and postoperative functional therapy, as described by Hat-void,6 may improve the stability of the correction. Improving the techniques for neuromuscular rehabilitation in preschool children is part of the challenge of this new modality of treatment. In addition to the application of distraction osteogenesis to craniomaxillofacial disorders, this modality of treatment may become important in the management of a variety of alveolar deformities. Clinical use of distraction osteogenesis within the alveolus requires development of miniature, intraoral devices that can achieve multiple-axis transport of small bone segments. References 1. Ilizarov GA: The principles of the Ilizarov method. Bull. Hospital Joint Dis Orthop Inst 48:1, 1988 2. McCarthy JG, Schreiber J, Karp N, et al: Lengthening of the human mandible by gradual distraction. Plast Reconstr Surg 89:1, 1992 3. Tschakaloff A, Losken, HW, Mooney MP, et al: Internal calvarial bone distraction in rabbits with experimental coronal suture immobilization J Craniofac Surg 5:318, 1994 4. Takato T, Harii K, Hirabayashi S, et al: Mandibular lengthening by gradual distraction: Analysis using accurate skull replicas. Br J Plast Surg 46:686, 1993 5. Moore M, Guzman-Stein G, Proudman TW, et al: Mandibular lengthening by distraction for airway obstruction in TeacherCollins syndrome. J Craniofac Surg 5:22, 1994 6. Harvold EP: Treatment of Hemifacial Microsomia. New York, NY, Liss, 1983
Surg
Distraction Osteogenesis in Maxillofacial Surgery Using In ternal Devices: Review MARTIN
CHIN,
of Five Cases
DDS,” AND
BRYANT
A. TOTH,
MDT
Purpose: The purpose of this report is to show the feasibility and potential advantages of using internal devices for distraction osteogenesis in the management of maxillofacial skeletal deficiencies. Patients and Methods: Distraction osteogenesis was used to correct a variety of maxillofacial skeletal deformities in five patients. One patient underwent bilateral Le Fort III advancement aided by distraction, three patients underwent mandibular ramus lengthening, and one patient underwent segmental alveolar reconstruction by distraction. The devices were activated by either a transcutaneous or transmucosal pin. After achievement of the desired skeletal transport, the activating pins were disengaged and removed from the distraction device. This allowed the distraction device to remain submerged and to stabilize the site of the consolidating bone. Results: All patients achieved lengthening of their jaws. However, premature consolidation was noted in two patients, and one patient had significant relapse. Conc/usions: Development of internal distraction devices is important to address the limitations of currently available biphasic systems. Potential benefits of internal devices include 1) elimination of skin scarring caused by translation of transcutaneous fixation pins, 2) improved patient compliance during the fixation or consolidation phase because there is no external component, and 3) improved stability of the attachment of the device to the bone.
Ilizarov’ is credited with defining the biologic basis and establishing an armamentium to allow practical, clinical use of skeletal distraction to regenerate bone for management of a variety of limb deformities. Early clinical applications of distraction osteogenesis for the correction of maxillofacial deformities have relied on orthopedic devices to achieve transport and fixation of the bone. McCarthy et al2 reported use of a miniaturized Hoffman device to lengthen human mandibles. Tschakaloff et al” described a technique to internalize a distraction transport system for experimental manip-
ulation of calvarial sutures in rabbits. Practical application of this technology to pediatric maxillofacial surgery requires modification of the orthopedic armamentarium, surgical technique, and distraction protocol to address the special features of the pediatric facial skeleton and special management needs of the child. Patients
Five patients underwent distraction osteogenesis. Two of the patients underwent bilateral distraction. Ages ranged from 2 to 17 years. Each patient had a custom distraction device fabricated. Articulated dental models, dental radiographs, three-dimensional computed tomography (CT) images, and milled skeletal models from CT data were used to plan the surgery and fabricate the distracters. The design of each distractor was determined by 1) the desired vector and magnitude of skeletal correction, 2) dysmorphology of
Received from California Pacific Medical Center, San Francisco, CA. * In private Practice, Oral and Maxiilofacial Surgery. t In private Practice, Plastic and Reconstructive Surgery. Address correspondence and reprint requests to Dr Chin: 2100 Webster St, Suite 303, San Francisco, CA 94115. 0 1996 American
Association
of Oral and Maxillofacial
and Methods
Surgeons
0278-2391/96/5401-0009$3.00/O
45
46
DISTRACTION
OSTEOGENESIS
FIGURE 1. 2 $-year-old boy with right craniofacial microsomia. A, Preoperative deficiency of right facial contour. B, CT three-dimensional reformation showing cant of mandible. C, CT three-dimensional reformation showing absence of glenoid fossa. D, CT model used as template to fabricate distractor. E, Distractor in place before mucosal closure. F, Distractor in place, activation pin removed, device submerged. G, Distractor extended at time of removal. H, Postdistraction improvement in facial contour.
the distraction site, 3) access for placement of the device and osteotomy, 4) access for the placement of the activating pin, and 5) anticipated patient cooperation with the device activation process. The distraction devices consisted of bone plates fabricated to engage threaded K-wires. When the threaded rod was turned, the attached bone plates separated. The skeletal fragments were transported with the attached
plates. One patient required incorporation of a rightangled gearbox mechanism to allow transoral access for activation. All devices were stabilized to the skeletal fragments with 2-mm diameter self-tapping screws. All of the devices for mandibular distraction were placed transorally. Two patients had transmucosal activating pins that were activated by a key introduced through the mouth. Two patients had transcutaneous
CHIN
AND
TOTH
47
48
FIGURE 2. 12-year-old boy with Pfeiffer syndrome. A, Preoperative facial profile showing midface retrusion. B, Preoperative lateral cephalometric radiograph showing Class III relationship. C, Distraction bone plates for right and left zygoma. D, Distraction bone plate in placed, left zygoma.
pins with removable, external knobs. The patient undergoing Le Fort III advancement by distraction had bilateral distracters placed via the coronal access used to perform the osteotomies. Bilateral, transcutaneous pins were used to activate the Le Fort III distracters. Both the transcutaneous and transmucosal activating pins were locked into the distracters in such a manner that they could be disengaged and removed after the
DISTRACTION
OSTEOGENESIS
CHIN
AND
TOTH
FIGURE 2. (Conr’d). E, Submentovertex radiograph showing orientation of distracters. F, Transcutaneous activation pin being removed. G, Postoperative facial profile showing improved convexity. H, Postoperative lateral cephalometric radiograph showing improved facial proportions.
completion of skeletal transport. The mandibular osteotomies were all performed by a transoral approach. The latency period, the delay between the osteotomy and onset of distraction, ranged from 0 to 5 days. The rate of distraction varied from 1 to 3 mm per day. The amount of immediate distraction, the separation of the osteotomy at the time the device is placed, ranged from 4 to 12 mm. Results All patients achieved clinical lengthening of their skeletal deformities. One patient experienced significant relapse of mandibular lengthening. In two cases, the distraction sites were reentered after 5 months to recover the distraction devices. In both of these cases, examination showed the distraction sites to be well consolidated and that the distraction devices remained fixed to the bone. Two patients had premature consolidation of the distraction sites. One patient with premature consolidation required surgery to mobilize the distraction site to complete the distraction. Another patient, undergoing bilateral mandibular distraction,
had an expansion screw break and required replace the component.
surgery
to
Report of Cases Case I A 2’/,-year-old boy with right craniofacial microsomia (Fig 1A) underwentosteotomy and placement of an internal distraction device with a transcutaneous activating pin. A CT scan with three-dimensional reformation demonstrated the extent of the deformity and absence of the right glenoid fossa (Fig lB, C). CT data were inputted into a CNC (computer numeric control) milling machine to produce a mandibular replica. The replica was used in the model surgery and to fabricate the distraction device (Fig 1D). The osteotomy and placement of the distraction device were performed through a mucosal incision such as used in sagittal split osteotomies. The osteotomy was mobilized and distracted by 4 mm at the time of surgery. The distraction device was placed on a subperiosteal plane and fixed to the mandibular fragments with 2-mm cortex screws (Fig IE). After a 5-day latency period, distraction was begun and proceeded at 0.25 mm, four times a day. The device was activated by a transcutaneous submandibular pin. After 7 days, the distractor encountered resistance, and the further transport could not be achieved. The patient was returned to the operating room,
50 where examination showed a dense, noncompliant tissue mass adjacent to the lingual periosteum. An osteotome was used to divide the tissue, and it was confirmed that the device was able to distract the segments further. After a total of 17 mm of distraction was achieved, the transcutaneous pin was removed (Fig lF), and the skin penetration site was allowed to heal. Five months after the initial procedure, the patient was returned to the operating room for removal of the distractor. The bone filling the distraction site was firm and stable (Fig 1G). The morphology of the bone followed the contour of the distractor. The width of the newly formed bone was greater than the native ends. There was no evidence that the subperiosteal presence of the distractor hindered bone formation. Lengthening of the mandibular ramus resulted in an improvement in the facial contour (Fig 1H). Case 2 A lZyear-old boy with Pfeiffer’s syndrome had severe midface hypoplasia involving the orbits, zygoma, and maxilla. At the age of 7 years, he underwent orbitocranial reconstruction with advancement of the supraorbital bar and frontal bones. The current procedure involved a Le Fort III osteotomy with advancement assisted by distraction. Figure 2A and B shows the preoperative facial profile and radiograph. The zygoma, inferior orbits, and nasomaxillary complex were mobilized as a single unit, and the midface was advanced 10 mm during surgery. Distracters were then fixed to the osteotomy sites in the malar regions using 2-mm cortex screws (Fig 2C, D, E). For activation, each distractor incorporated a transcutaneous pin that emerged in the infraorbital region (Fig 2F). Postoperatively, the distracters were activated 0.5 mm four to six times per day; no latency period was observed. After 5 days, the right distractor had moved 9 mm and the left 11 mm. The difference in right versus left distraction allowed correction of an asymmetry in the maxillary dental midline. The postoperative photograph and lateral cephalometric radiograph demonstrate the improved relationship between the midface, mandible, and cranium (Fig 2G, H). The combination of intraoperative movement and postoperative distraction translated the midface 19 and 21 mm on the right and left, respectively. On the fifth postoperative day, the transcutaneous pins were disengaged, and the patient was discharged.
DISTRACTION
OSTEOGENESIS
lus, lower incisors, and overlying mucosa had been avulsed. The result was a residual alveolus lacking in width and height (Fig 4A). There was also a deficiency in mucosa. The prosthodontist requested placement of two osseointegrated implants. Orthodontic treatment had closed the edentulous space to accommodate the width of two incisors. The deficiency in the edentulous ridge made ideal implant placement impossible without reconstructing the site or compromising the periodontal health of the adjacent teeth. The treatment plan involved transporting a segment of alveolus vertically into the deficient area. The superior, knife-edge ridge was resected and a segmental osteotomy created a block of alveolus for vertical transport (Fig 4B). A threaded pin was used to fix the fragment, and a threaded bone plate was used as anchorage for the pin (Fig 4C). A latency period of 5 days was observed. The distraction then proceeded at 1 mm per day for 9 days. The pin was then left in place for 10 days without activation, at which time it was unscrewed and removed. There was a marked improvement in the width and height of the alveolus (Fig 4D, E). The site was reentered after 6 weeks to recover the anchoring plate and to place osseointegrated implants. At the time of reentry, the segment was clinically stable (Fig 4F) and the increased bone mass made the site suitable for placement of endosseous implants. Case 5 A 4-year-old girl with Goldenhar syndrome underwent distraction osteogenesis of the left mandible. The child had a canted occlusal plane typical of primary ramus hypoplasia. Figure 5A shows the preoperative view of the patient. The facial contour has been overcorrected, with the chin deviating to the right side. The surgical procedure involved a modified sagittal split performed on the left ramus. The mandibular nerve was isolated as it entered the mandibular foramen. A horizontal osteotomy was placed through the medial cortex above the foramen. A second, parallel osteotomy was placed through the lateral cortex of the ramus approximately 10 mm inferior to the previous osteotomy. A short, vertical osteotomy along the anterior border of the ramus then connected the two horizontal cuts. A periosteal elevator was used to separate the osteotomy. The result was a sagittal osteotomy with only 10 mm of overlap. The osteotomy site was displaced and
Case 3 A 5-year-old boy with micrognathia, mandibular arthrogryposis, and an open bite underwent bilateral distraction of the mandibular rami. Oblique osteotomies were performed through the mandibular angles, and bilateral distracters were placed. Each distractor was activated by a transcutaneous submandibular pin. Marked resistence to mandibular advancement was noted at the time of distractor placement. No latency period was observed. The pins were activated 0.5 mm four times a day or 2 mm per day. Figure 3 shows the distraction devices in the extended position. After achieving 10 mm for transport, the right distractor fractured. The patient was returned to surgery to replace the broken component. The d&actors were activated to a total transport of 18 mm, after which they were disengaged. Postoperative cephalometric radiographs showed significant relapse in the correction. Case 4 A 17-year-old girl was involved in an automobile accident when she was 14 years old. The anterior mandibular alveo-
FIGURE 3. Panorex of a 5-year-old boy with micrognathia showing bilateral distraction devices in extended position. The transcutaneous activation keys have been removed.
CHIN AND TOTH
5-l
FIGURE 4. 17-year-old girl with traumatic defect of alveolus. A, Preoperative view of alveolar ridge showing width deficiency. B, Preparation of mandibular segment for vertical transport. Note superior aspect of the ridge is to be resected. C, Transmucosal screw for transport of the fragment. D, Postdistraction alveolar ridge showing improvement in width. E, Postdistraction alveolar ridge showing improvement in height. F, Alveolar ridge width at the time of osseointegrated implant placement. the distraction device positioned and fixed with 2-mm selftapping screws. The design of the device incorporated three telescopic components that could be activated independently (Fig 5B). At the time of surgery, two of the telescopes were activated to achieve an intraoperative ramus lengthening of 12 mm (Fig 5C). The third expansion compon&t was-reserved for postoperative distraction and could be periodicallv activated by a ‘transmucosal key. The activating rod was positioned through the mucosal incision, adjacent to the posterior molar (Fig 5D). A latency period of 5 days was ob-
served. Distraction then proceeded at 0.5 mm two to four times a day. By the 14th postoperative day, the total distraction had reached 25 mm, and the transmucosal pin was removed. Figures 5E and F shows the final result.
Discussion McCarthy et al2 and others4,5 have demonstrated the of using distraction osteogenesis to correct
feasibility
DISTRACTION
FIGURE 5. A 4-year-old girl with Goldenhar syndrome. and activation. C, Distractor at time of placement, prior Postoperative improvement in facial contour. F, Posterior
OSTEOGENESIS
A, Preoperative deficiency of left facial contour. B, Distractor for transoral placement to mucosal closure. D, Appearance of removable, transmucosal activation port. E, open bite as a result of vertical ramus lengthening.
mandibular deficiencies. External distraction hardware anchored by transcutaneous pins was used to achieve transport and stabilization of the skeletal fragments. Development of internal distraction devices is necessary to make the treatment acceptable in the mainstream practice of pediatric maxillofacial surgery. The cases presented demonstrate that internal devices can be used to manage a variety of skeletal deficiencies.
Internalization of distraction hardware also allows application of the technology to a wide range of anatomic locations. Because the devices were designed to be submerged, they provided internal fixation that usually does not require maintenance. Newly formed bone is supported by the distraction device, which serves as a bone plate in the fixation phase of treatment. Because the devices were placed by a transoral approach, there
CHIN
AND
TOTH
are no skin incisions and limited risk to the branches of the facial nerve. Movement of large skeletal fragments, such as in Le Fort III advancements, typically require overcoming major resistance from the soft tissue envelope. Incremental movement using distraction mechanics allows displacement of fragments over large distances because the soft tissue is allowed to accommodate slowly. By combining the conventional Le Fort III osteotomy with postoperative gradual distraction, a correction of 20 mm was achieved in case 2. In addition, the axis of correction and method of fixation were controlled by the distraction device. The results of these early cases raise a number of questions that will need to be addressed by long-term follow-up and careful study of future cases. Protocols accepted in adult orthopedic distraction osteogenesis may not be directly applicable to pediatric maxillofacial surgery. The rate of distraction and length of latency before the onset of distraction need further study. There is a clear risk of premature consolidation of the osteotomy site if the rate of distraction is too slow. If the parents have difficulty activating the device or if the latency period is too long, premature consolidation may also occur. This complication is of particular concern in very young patients who seem to consolidate very rapidly at the distraction sites. Because of these concerns, we have modified the surgical technique and distraction protocol. Our procedure for mandibular lengthening by distraction is as follows: The osteotomy involves isolation of the neurovascular bundle so it is tethered by only the distal fragment. This is done by performing a modified sagittal split osteotomy. Isolation of the neurovascular bundle allows major displacement of the osteotomy at the time of surgery. Access while performing the modified sag&al osteotomy allows for direct visualization and protection of both the lingual and inferior alveolar nerves. Displacement of the fragments before placement of the distraction device results in an increase in the magnitude of distraction in a short period.
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In addition, the axis of displacement before placement of the distractor may be different from the axis achieved by the distractor. The combined movement may produce an improvement in anatomic correction, but it requires careful planning. The long-term effect of early skeletal correction with distraction osteogenesis is unclear. Further study is required to evaluate the potential of early surgery to limit compensatory growth abnormalities. One of the current challenges is to determine how best to achieve a stable neuromuscular matrix to support the reconstructed skeleton. Patients with mandibular arthrogrypotic features are particularly challenging from this standpoint. Combining distraction with preoperative muscular conditioning and postoperative functional therapy, as described by Hat-void,6 may improve the stability of the correction. Improving the techniques for neuromuscular rehabilitation in preschool children is part of the challenge of this new modality of treatment. In addition to the application of distraction osteogenesis to craniomaxillofacial disorders, this modality of treatment may become important in the management of a variety of alveolar deformities. Clinical use of distraction osteogenesis within the alveolus requires development of miniature, intraoral devices that can achieve multiple-axis transport of small bone segments. References 1. Ilizarov GA: The principles of the Ilizarov method. Bull. Hospital Joint Dis Orthop Inst 48:1, 1988 2. McCarthy JG, Schreiber J, Karp N, et al: Lengthening of the human mandible by gradual distraction. Plast Reconstr Surg 89:1, 1992 3. Tschakaloff A, Losken, HW, Mooney MP, et al: Internal calvarial bone distraction in rabbits with experimental coronal suture immobilization J Craniofac Surg 5:318, 1994 4. Takato T, Harii K, Hirabayashi S, et al: Mandibular lengthening by gradual distraction: Analysis using accurate skull replicas. Br J Plast Surg 46:686, 1993 5. Moore M, Guzman-Stein G, Proudman TW, et al: Mandibular lengthening by distraction for airway obstruction in TeacherCollins syndrome. J Craniofac Surg 5:22, 1994 6. Harvold EP: Treatment of Hemifacial Microsomia. New York, NY, Liss, 1983
