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Automated Continuous Mandibular Distraction Osteogenesis: Review of the Literature
J Oral Maxillofac Surg 70:407-416, 2012
Automated Continuous Mandibular Distraction Osteogenesis: Review of the Literature Batya R. Goldwaser, DMD,* Maria E. Papadaki, DMD, MD,† Leonard B. Kaban, DMD, MD,‡ and Maria J. Troulis, DDS, DMSc§ Purpose: Current devices for mandibular distraction osteogenesis (DO) are complex and require
significant patient or family skill during active distraction. Successful development of an automated, continuous distraction device would eliminate the need for patient participation in this process. The purpose of this study was to comprehensively review devices currently in development for continuous DO and to identify and evaluate the achieved successes and remaining problems. Materials and Methods: A PubMed search of the English language literature in October 2008 using the keywords automatic or automated or continuous or hydraulic or motor or magnetic or spring and distraction osteogenesis was performed. The search included all technical notes, animal studies, and human studies describing the use of any automated continuous distraction device for the mandible. Excluded were studies using distraction devices employing hydraulics, motors, or springs that did not distract automatically and continuously and devices used for bones other than the mandible. Results: The search returned 97 matches. Of these, 12 articles were selected as relevant to this review based on the inclusion and exclusion criteria detailed above. Eight distinct devices for automated, continuous DO were described in these reports and evaluated in this review. These included motordriven, spring-mediated, and hydraulically powered distractors. Conclusions: The abundance of research currently underway to develop a continuous distractor highlights the clinical demand for, and usefulness, of such a device. Despite many advances and promising results, significant problems remain to be overcome before any of these devices gain widespread clinical acceptance. © 2012 Published by Elsevier Inc on behalf of the American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 70:407-416, 2012
Traditional surgical techniques for skeletal expansion include osteotomies, acute movements of variable magnitude, and the necessity for bone grafts. Problems include donor site morbidity, unpredictable resorption of large grafts, and the risk of relapse because of soft tissue resistance to large skeletal movements.
Many of these limitations can be avoided by the use of distraction osteogenesis (DO) to lengthen or expand the skeleton. DO is a technique first described for long bone lengthening by Codivilla in 19051 and Abbott in 1927.2 In 1969 Ilizarov3 published the first of a series of articles documenting his vast
Received from the Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston, MA. *Resident, Massachusetts General Hospital; Student Fellow, Oral and Maxillofacial Surgery, Synthes/Massachusetts General Hospital. †Instructor, Harvard School of Dental Medicine, AO/Synthes; MGH Fellow, Pediatric Oral and Maxillofacial Surgery. ‡Walter C. Guralnick Professor and Chair. §Associate Professor and Director, Residency Training Program.
This study was funded in part by the Hanson Foundation (Boston, MA), the Massachusetts General Hospital, OMFS Education/ Research Fund, and the NIH SBIR Grant (5R44 DE 014803-03). Address correspondence and reprint requests to Dr Troulis: Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, 55 Fruit ST, Boston, MA 02114; e-mail: [email protected] © 2012 Published by Elsevier Inc on behalf of the American Association of
Oral and Maxillofacial Surgeons 0278-2391/12/7002-0$36.00/0 doi:10.1016/j.joms.2011.01.042
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408 clinical experience and his pioneering research in the biology of DO. As a result, the technique achieved wide acceptance in orthopedics and Ilizarov deservedly became known as the “Father of Distraction Osteogenesis.” The standard distraction protocols currently in use are identical to those first described by Ilizarov.4 In 1973 Snyder et al5 performed the first mandibular distraction procedure in a canine model, and in 1992 McCarthy et al6 reported the first use of DO to lengthen the mandible in patients with first and second pharyngeal arch deformities. In 1993 Perrott et al7 used DO to widen the mandible. Since then distraction has increasingly been used to treat various craniomaxillofacial deformities. Benefits of DO include the minimally invasive nature of the procedure, the ability to achieve movements of great magnitude without the need for a bone graft, and elimination of donor site morbidity. In addition, concurrent soft tissue histogenesis may decrease relapse.8 Nonetheless, currently available distraction devices are not ideal for the patient or the surgeon. The patient must adjust the manual control 2 or more times daily, often over long periods. Because noncompliance and device failure are leading causes of treatment failure, the patient requires numerous office visits to ensure proper distractor activation.9,10 Frequent radiographs may be required to measure the gap size and evaluate the vector of movement. In semiburied or external devices necessary for large movements, visible facial scars and psychosocial stress may result.11-14 Ilizarov15 documented that the ideal rate of lengthening is 1 mm/d, with faster rates resulting in fibrous or nonunion. The consolidation period (the time between end-distraction and filling of the defect with bone) is at least 2 times the number of millimeters of distraction in days. Because DO is most often used in patients who require large skeletal movements, the treatment time is lengthy. In light of these drawbacks, many research groups are working to design novel distraction devices that expand automatically and continuously. An automated mechanism would eliminate the need for patient compliance and decrease the frequency of postoperative visits for patient supervision. It has also been reported that continuous distraction may be carried out at rates up to 2 mm/d with formation of bone in the gap. This would allow greater distraction distances in a shorter period, without sacrificing bone quality.14-19 The purpose of this study is to provide a comprehensive review of devices currently in clinical or experimental use for automated, continuous, mandibular DO and to identify and evaluate the achieved successes and remaining challenges.
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Materials and Methods A PubMed search of the English language literature in October 2008 using the keywords automated or automatic or continuous or hydraulic or motor or magnetic or spring and distraction osteogenesis was performed. All technical notes, animal studies, and human studies describing the use of any automated, continuous distraction device in the mandible were included in this review. Studies of distraction devices employing hydraulics, motors, magnets, or springs that did not distract automatically and continuously and studies with insufficient detail about the devices were excluded.
Results The search returned 97 matches, of which 12 described automated, continuous DO devices for the mandible. These were selected as relevant to this review based on the inclusion and exclusion criteria detailed above. Eleven studies were performed in animals and 1 in humans, with 8 distinct devices for automated continuous mandibular DO described and evaluated. The devices were classified into 3 categories based on the method of power: motor-driven, spring-mediated, and hydraulic (Table 1). MOTOR-DRIVEN
In 1996 Schmelzeisen et al20 developed one of the earliest continuous distractors and tested it in 3 Göttingen minipigs (4 months old, 9 kg). The device consisted of 2 gliding plates fixed to the lingual side of the mandible (Fig 1). A 3.2-W motor attached to the posterior plate and 2 lithium batteries set on a timer provided impulses of 10 ms every 6 minutes (for 1 mm of distraction per day). The researchers inserted the battery-powered unit into a subcutaneous pocket on the animal’s neck and attached it to the motor by a cable. Active distraction continued for 14 to 21 days. Clinically, massive callus formation around the osteotomy occurred in 1 pig. The ascending ramus of another pig fractured and this animal was sacrificed early. In the third, a gear broke and had to be replaced surgically and infection occurred. A lateral view radiograph was used to document 11 mm of distraction in 21 days in 1 pig and 13 mm in 14 days in another. Histologic examination of 1 specimen at end DO (21 days) showed early bone formation at the distal edge of the gap and small amounts of lamellar bone at the proximal edge. Ploder et al21,22 in 1999 and 2002 tested another motor-driven device in 8 adult male mountain sheep (54 kg). It consisted of a titanium-encased motor and a separate controller (Fig 2). A 3.6-V lithium battery powered the unit. The anterior mandible was ac-
409
15 Every 144 min
Zhou et al, 2004-200626,27 Kessler, Wiltfang et al, 2000-200128,29 Ayoub et al, 2001-200530-32 6
8
Idelsohn et al, 200425 5
Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
Mandible Sheep (n ⫽ 11) and human adults (n ⫽ 1)
15 Infinity
Maryland, United States Barcelona, Spain Mofid et al, 200324 4
7
Hong Kong Zheng et al, 200823
2
3
Beijing and Xi’an, China Erlangen, Germany Glasgow, UK
Hydraulic
9
New Zealand white rabbits (n ⫽ 20) and hybrid dogs (n ⫽ 10) Göttingen minipigs (n ⫽ 10)
Mandible (transport disc) Mandible (transport disc) Mandible Rabbits (n ⫽ 6)
Infinity
9
Mandible New Zealand white rabbits (n ⫽ 20)
Infinity
1.2
Mandible New Zealand white rabbits (n ⫽ 5)
Infinity
11
11.23 Mandible (anterior) Sheep (n ⫽ 8)
Every 60-120 min 8 increments/s
12 Every 6 min Mandible Göttingen minipigs (n ⫽ 3)
Motor (lithium battery) Motor (lithium battery) Motor (lithium battery) Spring (nickeltitanium) Spring (nickeltitanium) Spring (nickeltitanium) Hydraulic Hannover, Germany Vienna, Austria Schmelzeisen et al, 199620 Ploder et al, 199921,22 1
Location Author Device
Table 1. SUMMARY OF REVIEWED DEVICES
Device Type
Study Model
Site
Rhythm
Average Distraction (mm)
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cessed through a submandibular incision and the distractor was fixed across an osteotomy. The controller was buried in a subcutaneous pocket and sutured to the sternocleidomastoid muscle. After a 5-day latency period, the investigators transcutaneously activated the device. The active distraction period lasted 14 days, followed by neutral fixation for 6 to 7 weeks. Distraction occurred at 0.04 mm/hour, for 1 mm of distraction per day. Clinically, all animals showed unilateral cross-bites and stable mandibles at sacrifice. The length of distraction ranged from 1.7 to 17.1 mm (active distraction range, 2 to 17 days) as measured on the specimens and the device. Radiographically, the gap appeared radiolucent during distraction and slightly radiodense after 5 weeks of fixation. Histologically, a spherical callus developed around the gap and consisted of an irregular fibrous zone between areas of membranous and/or cartilaginous woven bone at the native bone edge. Various size islands of fibro- and hyaline cartilage were seen on the lingual side of the callus, where the periosteum was left intact. This may be a sign of instability. Most recently, Zheng et al23 studied another motordriven distractor in 5 adult New Zealand white rabbits (3 to 3.8 kg). Unilateral vertical mandibular osteotomies were made immediately anterior to the first premolar (Fig 3). The distractors were fixed to the mandible perpendicular to the osteotomy. After a 3-day latency period, an automatic driver fixed on a plastic collar was attached to the distractor and activated 8 steps per second for a total rate of 2 revolutions (0.9 mm) per day. Active distraction continued for 11 days, followed by a 4-week consolidation period. Clinically, all rabbits developed a severe crossbite and overgrowth of incisors and all reached the planned advancement. Radiographically, the osteotomy side showed bony continuity and with bone fill in the gap that was less radiodense than the host bone. Microcomputed tomography demonstrated partial corticalization across the gap. Histologically, a mixture of woven and mature lamellar bone with rich fibrovascular stroma was seen. SPRING-MEDIATED
In 2003 Mofid et al24 studied spring-mediated mandibular DO devices in 20 adult New Zealand white rabbits (4 kg). Their device consisted of a 55-mm-long nickel-titanium alloy bent into an arc shape, reinforced at both ends with pinballs, and secured to the mandible with stainless steel wires (Fig 4). To prevent activation during the 12-day latency phase, the researchers left a second stainless steel wire connecting the pinballs to each other; they reopened the incision to sever this wire when beginning active distraction. Five animals were removed from the study because of infection, nonunion, or device failure. A lateral radio-
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FIGURE 1. Motor-driven device with stainless steel plates on the lingual side of the mandible after a 13-mm distraction. Reprinted from Schmelzeisen R, Neumann G, von der Fecht R: Distraction osteogenesis in the mandible with a motor-driven plate: A preliminary animal study. Br J Oral Maxillofac Surg 34:377, 1996 with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
graph was used to show a mean length of the distraction gap of 1.2 mm, with a maximum of 3.7 mm, after 6 weeks of distraction. Histologic examination showed complete bone bridging with no cartilage or
fibrous tissue in all but 1 specimen. At the native bone-callus junction, the remodeled regenerate was distinct but looked similar to native bone. Although the quality of new bone compared well with that
FIGURE 2. Distraction system consisting of a titanium-encased motor and a separate controller placed on the mandible of an animal skull and shown in a lengthened position (arrow). Reprinted from Ploder O, Mayr W, Schnetz G, et al: Mandibular lengthening with an implanted motor-driven device: Preliminary study in sheep. Br J Oral Maxifac 37:274, 1999, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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FIGURE 3. A, Automated system comprised of a driving unit (A), flexible shaft (B), and mounting mechanism (C). The torque generated by the driving unit is transmitted to the activation rod of a distractor (D) through the flexible shaft and mounting mechanism. B, The driving unit (A) is fixed on a plastic collar and connected by a flexible shaft (B) to an external distractor (C) placed on the rabbit mandible. Reprinted from Zheng LW, Cheung LK, Ma L, et al: High-rhythm automatic driver for bone traction: An experimental study in rabbits. Int J Oral Maxillofac Surg 37:737, 2008, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
from traditional distraction methods, the force of this device proved insufficient to produce a clinically significant bone lengthening. Idelsohn et al25 designed another nickel-titanium alloy device to study mandibular transport DO in 6 female rabbits (12 months old, 3 kg). They performed an 8-mm segmental mandibulectomy at the mandibu-
lar body and a corticotomy 5 mm distal to the gap. After a 5-day latency period, they placed commercially available nickel-titanium orthodontic springs between the proximal mandible and the transport segment and left these in place for 2 months (Fig 5). Clinical continuity and normal dimensions were observed in all specimens. Radiographically, 2 to 5 mm
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FIGURE 4. Shape memory alloy spring-distractor model. A 55-mm segment of nitinol secured at either end with a pinball is bent into an inferiorly based arc and secured to the hemimandible with stainless steel wire. Reprinted from Mofid MM, Inoue N, Tufaro AP, et al: Spring-mediated mandibular distraction osteogenesis. J Craniofac Surg 14:757, 2003, with permission from Mutaz B. Habal, MD. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
of lengthening was achieved after 1 week of distraction, and 7 to 13 mm by 3 weeks. Histologically, the trabeculae were oriented longitudinally after the direction of the distraction force. Cells typical of intramembranous ossification were observed, ie, mesenchymal tissue with large numbers of osteoblasts starting to be surrounded by bone lacunas with no sign of cartilage. Zhou et al26 also tested a fully buried, nickel-titanium spring to lengthen the mandibular ramus of 20 New Zealand white male rabbits (6 months old, 3 kg; Fig 6). Four were used as controls. Using a submandibular incision, the ascending ramus and condyle (15-mm segment) were resected by transverse osteotomy, and a transport disc was created in the remnant ramus by L-shaped osteotomy. Six rabbits were sacrificed after 6 days. In these animals the overall rate of distraction slowly decreased with each day of activation: 4 mm on the first day, 2 mm on the second day, 1 mm on the third day, 1.5 mm on the fourth day, 0.5 mm on the fifth day, and 0 mm on the sixth day. The other animals were sacrificed after an 8-week consolidation period. Clinically, no infections occurred and the junction between the new and old bone was
MANDIBULAR DISTRACTION OSTEOGENESIS
morphologically indistinguishable. Radiographically, ossification was documented and the trabeculae were oriented parallel to the ascending ramus. Histologically, longitudinally oriented trabecular bone with regularly arranged collagen bundles was observed. Occasional cartilage was also seen. In 2006 the same group tested this spring-loaded device in 10 hybrid dogs (3 years old, 20 to 25 kg).27 A 40-mm segmental mandibulectomy was made through a submandibular incision from the fourth premolar to the first molar. A second osteotomy was made between the second and third premolars, creating a tooth-bearing transport disc. Distraction began immediately and continued for 28 days when the transport disc reached the proximal segment. The rate of movement began at 3 mm/d and decreased to 1 to 1.5 mm on the following days. After a 12-week consolidation period, the animals were sacrificed. In all animals, the entire defect filled in with new bone that appeared ossified radiographically and was continuous with the native mandible. On histology, new bone trabeculae were organized longitudinally on the distraction side and crosswise on the compression side. HYDRAULIC
Various researchers have used hydraulic forces to drive distractors. Kessler et al28 and Wiltfang et al29 tested a hydraulic device in 6 female Göttingen minipigs. After performing a mandibular osteotomy, they fixed a 9-mm diameter steel cylinder and piston to the proximal and distal segments of the mandible (Fig 7). A flexible
FIGURE 5. Novel superelastic shape memory alloy distractor, showing shape memory alloy springs (S), bone plates to fix the mandible and not allow movements (P), segment that is going to be displaced forward (B), and newly formed bone (C). Reprinted from Idelsohn S, Pena J, Lacroix D, et al: Continuous mandibular distraction osteogenesis using superelastic SMA. J Mater Sci Mater Med 15:542, 2004 (Figure 4) with kind permission from Springer Science and Business Media. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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413 tube connected the internal distractor to an external steering unit on the animal’s back. The unit held a noncompressible fluid kept under constant pressure by a fluid reservoir. After a 7-day latency period, they distracted the mandibles 1.5 mm/d for 8 to 10 days, resulting in 14 to 15 mm of new bone formation. The device was activated manually for discontinuous DO in some animals and continuously using pressure control in others. During the fixation phase, a connectable pressure receptor could be attached to measure the daily pressures. Compared with intermittent distraction, where high pressure peaked immediately after activation and fluctuated with low pressure 2 to 3 hours later, pressure remained at a constant moderate level with continuous distraction. Ultrasound and histologic examinations in the 2 groups showed a central fibrous zone that was poorly mineralized with longitudinally oriented collagen bundles. During fixation, the fibrous zone ossified and woven bone regenerated. There was rare cartilage found. However, in the continuous group, the bone was more ossified on the ultrasound image and more mature on the scanning electron microscopic image. In 2001 a group in Glasgow designed another automatic mandibular distractor using hydraulics.30,31 A tube connected identical internal and external nickel bellows, so compression of the external bellow caused extension of the implanted bellow. A batterydriven portable pump compressed the external bellows, forcing fluid through the connecting tube into the internal component (Fig 8). The movement of the external drive system corresponded with the bone distraction, eliminating the need for radiographs. The investigators tested this device in 11 sheep (24 months old, 55 kg). Three were controls and 8 under-
FIGURE 6. A, Nitinol spring distraction device. Top, Sites of osteotomy. Middle, Removed segment. Bottom, Fixation of the nitinol spring and other devices. Reprinted from Zhou HZ, Hu M, Hu KJ, et al: Transport distraction osteogenesis using nitinol spring: An exploration in canine mandible. J Craniofac Surg 7:944, 2006, with permission from Mutaz B. Habal, MD. B, Radiograph of the reconstructed mandibular ramus using nitinol spring transport distraction osteogenesis. Reprinted from Zhou HZ, Hu M, Yao J, et al: Transport distraction osteogenesis using nitinol spring: An exploration in canine mandible. J Craniofac Surg 15:727, 2004, with permission from Mutaz B. Habal, MD. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
FIGURE 7. Microhydraulic distractor in situ on a pig’s mandible. Reprinted from Wiltfang J, Kessler P, Merten H-A, et al: Continuous and intermittent bone distraction using a microhydraulic cylinder: An experimental study in minipigs. Br J Oral Maxillofac Surg 39:3, 2001, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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FIGURE 8. A, Immediate postoperative lateral oblique radiograph showing the surgical defect in a sheep. Reprinted from Ayoub AF, Richardson W: A new device for microincremental automatic distraction osteogenesis. Br J Oral Maxillofac Surg 39:359, 2001, with permission from Elsevier. B, Panoramic radiograph showing correction of facial asymmetry and the chin in the center of the face. Reprinted from Ayoub AF, Richardson W, Barbenel JC: Mandibular elongation by automatic distraction osteogenesis: The first application in humans. Br J Maxillofac Surg 43:326, 2005, with permission from Elsevier. C, In the sheep model, the internal component of the distraction device was fixed to the proximal segment of the mandible and to the transport disc using 3 bicortical screws at each site. Reprinted from Ayoub AF, Richardson W: A new device for microincremental automatic distraction osteogenesis. Br J Oral Maxillofac Surg 39:357, 2001, with permission from Elsevier. D, The distractor connected by a flexible drive cable, which was passed through a skin incision at the angle of the mandible, to an external plunger mounted in an ambulatory infusion pump. Reprinted from Ayoub AF, Richardson W, Barbenel JC: Mandibular elongation by automatic distraction osteogenesis: The first application in humans. Br J Oral Maxillofac Surg 43:326, 2005, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
went active distraction. Two of the 8 were excluded because of postoperative complications. A submandibular incision was used to access the mandibular body. A 25-mm segmental mandibulectomy was performed and a 20-mm tooth-bearing transport disc was made posterior to the defect. After a 1-day latency period, the device was activated to distract the transport disc 1 mm divided into 10 steps over 24 hours for 25 days. After an 8-week consolidation period, the animals were sacrificed. Bone formed on the tension
and compression sides; the disc moved 15 mm, resulting in 15 mm of new bone formation on the tension side and 10 mm on the compression side. There was clinical continuity of the regenerated and native bone, with normal morphology. Four animals had infections. Radiographically, the areas anterior and posterior to the transport disc were less radiodense at 2 weeks and became more radiopaque over time. At 8 weeks, the new bone and the transport disc had similar densities. On ultrasound, after 8
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weeks of consolidation, dense bands of calcified tissue were appreciated that looked similar to adjacent bone. Angiography performed before sacrifice showed the inferior alveolar artery and a substantial plexus of small vessels around the regenerate filled with contrast material. Histologically, the regenerate showed haversian systems of mature lamellar bone. The same research group published a case report in 2005 describing the successful use of this device to correct mandibular asymmetry in a 65-year-old man.32
Discussion When designing any new device, it is essential to identify and evaluate specific parameters that can be used as objective markers of success and failure. We have identified the following key features of a clinically useful distraction device whether continuous and/or automated or manual and discontinuous: small size; easily implantable; fully buried; biocompatible; sufficient force generation and maintenance; ability to measure force used; robust enough to withstand in vivo environments; simple design and activation; adjustability of rate, rhythm, and vector once treatment begins; automated with little patient involvement; predictability of distraction endpoint; ability to noninvasively and accurately measure progress of lengthening; need for few additional procedures after implantation. Although currently available and widely used distractors produce predictably successful results, significant problems remain, including size constraints, patient compliance issues, limitation of rate to 1 mm/d, durability issues, inability to measure actual forces of distraction, need for repeated radiation exposure to measure progress, a second procedure to remove the device, infection, and psychosocial effects from external parts. The motor-driven devices reviewed in this article address some of these issues. Two devices were fully buried and automatic and generated sufficient force to move the fragments.20-22 However, neither device consistently distracted 1 mm/d as intended.20,21 The third motor-driven device had an external driver, but this could be removed after the period of active distraction. In this case, distraction occurred as planned.23 None of the motorized device allowed the clinician to measure progress without taking radiographs, and only the third device allowed the clinician to adjust rate, rhythm, or direction once treatment began. The use of implanted motors running on battery power would require invasive procedures to change batteries or fix technical malfunctions, a likely requirement considering the motors’ complexity.20-22 This highlights the benefit of the device of Zheng et al,23 which keeps the driver external and removable.
415 In this review, 3 different spring-mediated devices were presented. The popularity of using springs to generate force stems from the simplicity of design, low cost, and commercial availability of materials. However, although spring devices are self-operating, their force is at a maximum early in distraction, when the spring is fully compressed, but gradually decreases as the spring expands. This is especially detrimental because the amount of force needed to distract increases over time. The finding in 2 springdevice studies that the distraction rate began at 3 to 4 mm/d and gradually decreased in rate over the following days illustrates this point.26,27 Furthermore, although each spring has a unique elasticity curve, spring devices do not offer the ability to control the motion of the segments (ie, rate and rhythm) or to adjust the force based on individual tissue resistance, making it difficult to predict the distraction endpoint.24,27 Directionality is also difficult to predict; most devices described only distracted linearly, although 1 model did use multidirectional vectors.24 The protocol cannot be adjusted without replacing the spring or removing it, and reversal is impossible. Two groups using spring-mediated devices demonstrated transport disc distraction only. It is therefore unclear whether similar results would occur in monofocal distraction. Although all spring designs were fully buried, infection was decreased but not completely eliminated.24,25,27 Two devices required a second incision to activate if the clinician desired a latency period, which added additional surgical risk.24,25 Interestingly, the spring devices shed light on the potential for faster distraction rates with continuous DO, because the investigators found no evidence of fibrous union with a rate of 2 or 4 mm/d with no latency period during the first part of treatment.26,27 This finding supports Ilizarov’s postulation that continuous DO would allow a faster rate.15 The 2 hydraulic distractors reviewed showed significant potential for further development. The 2 devices functioned automatically and required no daily intervention. One design could be used continuously or discontinuously, and the surgeon could interact with the system to adjust the protocol mid treatment.30 An important advantage of the device described by Kessler et al28 is its ability to measure the force applied to the segments, a valuable feature for future technical development and miniaturization of distractors. Nevetheless, the pressure sensor was somewhat removed from the actual site of the distractor and may not prove accurate. In addition, the 2 devices were semiburied with a tube exiting at the neck that may have caused some of the encountered infections.28,31 One of the hydraulic devices had the additional benefit of being able to measure the distance distracted without radiographs, and although
416 not in widespread use, this group has shown future potential with its case report of application in a human adult.30-32 The abundance of research currently under way to develop a continuous distractor highlights the clinical demand for and usefulness of such a device. Despite the promising results of many groups, significant challenges remain to be overcome before any of these devices gain broad clinical acceptance. Issues of infection, external scars, psychosocial stress, measurement of distractor gap without radiation, mid-course protocol adjustability, curvilinear distraction, size of device, and the need for multiple procedures must still be resolved. Thus, significant work remains. In an effort to improve existing discontinuous distractors and continuous distractors in development, the present investigators are working on a novel, buried, hydraulic, automated, continuous, curvilinear mandibular distractor (National Institute of Health, Small Business Innovation Research Grant 5R44 DE 01480303).33 The results of this project will be submitted in a subsequent report.
References 1. Codivilla A: On the means of lengthening in the lower limbs, the muscles and tissues which are shortened through deformity. Am J Orthop Surg 2:353, 1905 2. Abbott LC: The operative lengthening of the tibia and fibula. J Bone Joint Surg 9:128, 1927 3. Ilizarov GA, Deviatov AA: Surgical lengthening of the shin with simultaneous correction of deformities. Ortop Travmatol Protez 30:32, 1969 4. Ilizarov GA: The principles of the Ilizarov method. Bull Hosp Joint Dis Orthop Inst 48:1, 1988 5. Snyder CC, Levine GA, Swanson HM, et al: Mandibular lengthening by gradual distraction. Preliminary report. Plast Reconstr Surg 51:506, 1973 6. McCarthy JG, Schreiber J, Karp N, et al: Lengthening the human mandible by gradual distraction. Plast Reconstruct Surg 89:1, 1992 7. Perrott DH, Berger R, Vargervik K, et al: Use of a skeletal distraction device to widen the mandible: A case report. J Oral Maxillofac Surg 51:435, 1993 8. Castano FJ, Troulis MJ, Glowacki J, et al: Proliferation of masseter myocytes after distraction osteogenesis of the porcine mandible. J Oral Maxillofac Surg 59:302, 2001 9. van Strijen PJ, Breuning KH, Becking AG, et al: Complications in bilateral mandibular distraction osteogenesis using internal devices. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 96:392, 2003 10. Swennen G, Schliephake H, Dempf R, et al: Craniofacial distraction osteogenesis: A review of the literature: Part 1: Clinical studies. Int J Oral Maxillofac Surg 30:89, 2001 11. Hurmerinta K, Peltomäki T, Hukki J: Unexpected events during mandibular distraction osteogenesis. Scand J Plast Reconstr Surg Hand Surg 38:209, 2004 12. Ayoub AF, Duncan CM, McLean GR, et al: Response of patients and families to lengthening of the facial bones by extraoral distraction osteogenesis: A review of 14 patients. Br J Oral Maxillofac Surg 40:397, 2002
MANDIBULAR DISTRACTION OSTEOGENESIS 13. Primrose AC, Broadfoot E, Diner PA, et al: Patients’ responses to distraction osteogenesis: A multi-centre study. Int J Oral Maxillofac Surg 34:238, 2005 14. Kessler P, Neukam FW, Wiltfang J: Effects of distraction forces and frequency of distraction on bony regeneration. Br J Oral Maxillofac Surg 43:392, 2005 15. Ilizarov GA: The tension-stress effect on the genesis and growth of tissues: Part II. The influence of the rate and frequency of distraction. Clin Orthop 239:263, 1989 16. Djasim UM, Wolvius EB, Bos JA, et al: Continuous versus discontinuous distraction: Evaluation of bone regenerate following various rhythms of distraction. J Oral Maxillofac Surg 67: 818, 2009 17. Djasim UM, Mathot BJ, Wolvius EB, et al: Histomorphometric comparison between continuous and discontinuous distraction osteogenesis. J Cranio-Maxillofac Surg 37:398, 2009 18. Shetsov VI, Popkov AV: Limb lengthening in automatic mode. Orthop Traumatol Rehabi 30:403, 2002 19. Kessler PA, Merten HA, Neukam FW, et al: The effects of magnitude and frequency of distraction forces on tissue regeneration in distraction osteogenesis of the mandible. Plast Reconstr Surg 109:171, 2002 20. Schmelzeisen R, Neumann G, von der Fecht R: Distraction osteogenesis in the mandible with a motor-driven plate: A preliminary animal study. Br J Oral Maxillofac Surg 34:375, 1996 21. Ploder O, Mayr W, Schnetz G, et al: Mandibular lengthening with an implanted motor-driven device: Preliminary study in sheep. Br J Oral Maxillofac Surg 37:273, 1999 22. Ploder O, Kanz F, Randl U, et al: Three-dimensional histomorphometric analysis of distraction osteogenesis using an implanted device for mandibular lengthening in sheep. Plast Reconstr Surg 110:130, 2002 23. Zheng LW, Cheung LK, Ma L, et al: High-rhythm automatic driver for bone traction: An experimental study in rabbits. Int J Oral Maxillofac Surg 37:736, 2008 24. Mofid MM, Inoue N, Tufaro AP, et al: Spring-mediated mandibular distraction osteogenesis. J Craniofac Surg 14:756, 2003 25. Idelsohn S, Pena J, Lacroix D, et al: Continuous mandibular distraction osteogenesis using superelastic shape memory alloy (SMA). J Mater Sci Mater Med 15:541, 2004 26. Zhou HZ, Hu M, Yao J, et al: Rapid lengthening of rabbit mandibular ramus by using nitinol spring: A preliminary study. J Craniofac Surg 15:725, 2004 27. Zhou HZ, Hu M, Hu KJ, et al: Transport distraction osteogenesis using nitinol spring: An exploration in canine mandible. J Craniofac Surg 17:943, 2006 28. Kessler P, Wiltfang J, Wilhelm-Neukam F: A new distraction device to compare continuous and discontinuous bone distraction in mini-pigs: A preliminary report. J Craniomaxillofac Surg 28:5, 2000 29. Wiltfang J, Kessler P, Merten H-A, et al: Continuous and intermittent bone distraction using a microhydraulic cylinder: An experimental study in minipigs. Br J Oral Maxillofac Surg 39:2, 2001 30. Ayoub AF, Richardson W: A new device for microincremental automatic distraction osteogenesis. Br J Oral Maxillofac Surg 39:353, 2001 31. Ayoub AF, Richardson W, Koppel D, et al: Segmental mandibular reconstruction by microincremental automatic distraction osteogenesis: An animal study. Br J Oral Maxillofac Surg 39: 356, 2001 32. Ayoub AF, Richardson W, Barbenel JC: Mandibular elongation by automatic distraction osteogenesis: The first application in humans. Br J Oral Maxillofac Surg 43:324, 2005 33. Goldwaser BR: Novel device for automated continuous distraction osteogenesis: Preliminary results in minipigs. J Oral Maxillofac Surg 66:38, 2008
Automated Continuous Mandibular Distraction Osteogenesis: Review of the Literature Batya R. Goldwaser, DMD,* Maria E. Papadaki, DMD, MD,† Leonard B. Kaban, DMD, MD,‡ and Maria J. Troulis, DDS, DMSc§ Purpose: Current devices for mandibular distraction osteogenesis (DO) are complex and require
significant patient or family skill during active distraction. Successful development of an automated, continuous distraction device would eliminate the need for patient participation in this process. The purpose of this study was to comprehensively review devices currently in development for continuous DO and to identify and evaluate the achieved successes and remaining problems. Materials and Methods: A PubMed search of the English language literature in October 2008 using the keywords automatic or automated or continuous or hydraulic or motor or magnetic or spring and distraction osteogenesis was performed. The search included all technical notes, animal studies, and human studies describing the use of any automated continuous distraction device for the mandible. Excluded were studies using distraction devices employing hydraulics, motors, or springs that did not distract automatically and continuously and devices used for bones other than the mandible. Results: The search returned 97 matches. Of these, 12 articles were selected as relevant to this review based on the inclusion and exclusion criteria detailed above. Eight distinct devices for automated, continuous DO were described in these reports and evaluated in this review. These included motordriven, spring-mediated, and hydraulically powered distractors. Conclusions: The abundance of research currently underway to develop a continuous distractor highlights the clinical demand for, and usefulness, of such a device. Despite many advances and promising results, significant problems remain to be overcome before any of these devices gain widespread clinical acceptance. © 2012 Published by Elsevier Inc on behalf of the American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 70:407-416, 2012
Traditional surgical techniques for skeletal expansion include osteotomies, acute movements of variable magnitude, and the necessity for bone grafts. Problems include donor site morbidity, unpredictable resorption of large grafts, and the risk of relapse because of soft tissue resistance to large skeletal movements.
Many of these limitations can be avoided by the use of distraction osteogenesis (DO) to lengthen or expand the skeleton. DO is a technique first described for long bone lengthening by Codivilla in 19051 and Abbott in 1927.2 In 1969 Ilizarov3 published the first of a series of articles documenting his vast
Received from the Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, Harvard School of Dental Medicine, Boston, MA. *Resident, Massachusetts General Hospital; Student Fellow, Oral and Maxillofacial Surgery, Synthes/Massachusetts General Hospital. †Instructor, Harvard School of Dental Medicine, AO/Synthes; MGH Fellow, Pediatric Oral and Maxillofacial Surgery. ‡Walter C. Guralnick Professor and Chair. §Associate Professor and Director, Residency Training Program.
This study was funded in part by the Hanson Foundation (Boston, MA), the Massachusetts General Hospital, OMFS Education/ Research Fund, and the NIH SBIR Grant (5R44 DE 014803-03). Address correspondence and reprint requests to Dr Troulis: Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, 55 Fruit ST, Boston, MA 02114; e-mail: [email protected] © 2012 Published by Elsevier Inc on behalf of the American Association of
Oral and Maxillofacial Surgeons 0278-2391/12/7002-0$36.00/0 doi:10.1016/j.joms.2011.01.042
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408 clinical experience and his pioneering research in the biology of DO. As a result, the technique achieved wide acceptance in orthopedics and Ilizarov deservedly became known as the “Father of Distraction Osteogenesis.” The standard distraction protocols currently in use are identical to those first described by Ilizarov.4 In 1973 Snyder et al5 performed the first mandibular distraction procedure in a canine model, and in 1992 McCarthy et al6 reported the first use of DO to lengthen the mandible in patients with first and second pharyngeal arch deformities. In 1993 Perrott et al7 used DO to widen the mandible. Since then distraction has increasingly been used to treat various craniomaxillofacial deformities. Benefits of DO include the minimally invasive nature of the procedure, the ability to achieve movements of great magnitude without the need for a bone graft, and elimination of donor site morbidity. In addition, concurrent soft tissue histogenesis may decrease relapse.8 Nonetheless, currently available distraction devices are not ideal for the patient or the surgeon. The patient must adjust the manual control 2 or more times daily, often over long periods. Because noncompliance and device failure are leading causes of treatment failure, the patient requires numerous office visits to ensure proper distractor activation.9,10 Frequent radiographs may be required to measure the gap size and evaluate the vector of movement. In semiburied or external devices necessary for large movements, visible facial scars and psychosocial stress may result.11-14 Ilizarov15 documented that the ideal rate of lengthening is 1 mm/d, with faster rates resulting in fibrous or nonunion. The consolidation period (the time between end-distraction and filling of the defect with bone) is at least 2 times the number of millimeters of distraction in days. Because DO is most often used in patients who require large skeletal movements, the treatment time is lengthy. In light of these drawbacks, many research groups are working to design novel distraction devices that expand automatically and continuously. An automated mechanism would eliminate the need for patient compliance and decrease the frequency of postoperative visits for patient supervision. It has also been reported that continuous distraction may be carried out at rates up to 2 mm/d with formation of bone in the gap. This would allow greater distraction distances in a shorter period, without sacrificing bone quality.14-19 The purpose of this study is to provide a comprehensive review of devices currently in clinical or experimental use for automated, continuous, mandibular DO and to identify and evaluate the achieved successes and remaining challenges.
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Materials and Methods A PubMed search of the English language literature in October 2008 using the keywords automated or automatic or continuous or hydraulic or motor or magnetic or spring and distraction osteogenesis was performed. All technical notes, animal studies, and human studies describing the use of any automated, continuous distraction device in the mandible were included in this review. Studies of distraction devices employing hydraulics, motors, magnets, or springs that did not distract automatically and continuously and studies with insufficient detail about the devices were excluded.
Results The search returned 97 matches, of which 12 described automated, continuous DO devices for the mandible. These were selected as relevant to this review based on the inclusion and exclusion criteria detailed above. Eleven studies were performed in animals and 1 in humans, with 8 distinct devices for automated continuous mandibular DO described and evaluated. The devices were classified into 3 categories based on the method of power: motor-driven, spring-mediated, and hydraulic (Table 1). MOTOR-DRIVEN
In 1996 Schmelzeisen et al20 developed one of the earliest continuous distractors and tested it in 3 Göttingen minipigs (4 months old, 9 kg). The device consisted of 2 gliding plates fixed to the lingual side of the mandible (Fig 1). A 3.2-W motor attached to the posterior plate and 2 lithium batteries set on a timer provided impulses of 10 ms every 6 minutes (for 1 mm of distraction per day). The researchers inserted the battery-powered unit into a subcutaneous pocket on the animal’s neck and attached it to the motor by a cable. Active distraction continued for 14 to 21 days. Clinically, massive callus formation around the osteotomy occurred in 1 pig. The ascending ramus of another pig fractured and this animal was sacrificed early. In the third, a gear broke and had to be replaced surgically and infection occurred. A lateral view radiograph was used to document 11 mm of distraction in 21 days in 1 pig and 13 mm in 14 days in another. Histologic examination of 1 specimen at end DO (21 days) showed early bone formation at the distal edge of the gap and small amounts of lamellar bone at the proximal edge. Ploder et al21,22 in 1999 and 2002 tested another motor-driven device in 8 adult male mountain sheep (54 kg). It consisted of a titanium-encased motor and a separate controller (Fig 2). A 3.6-V lithium battery powered the unit. The anterior mandible was ac-
409
15 Every 144 min
Zhou et al, 2004-200626,27 Kessler, Wiltfang et al, 2000-200128,29 Ayoub et al, 2001-200530-32 6
8
Idelsohn et al, 200425 5
Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
Mandible Sheep (n ⫽ 11) and human adults (n ⫽ 1)
15 Infinity
Maryland, United States Barcelona, Spain Mofid et al, 200324 4
7
Hong Kong Zheng et al, 200823
2
3
Beijing and Xi’an, China Erlangen, Germany Glasgow, UK
Hydraulic
9
New Zealand white rabbits (n ⫽ 20) and hybrid dogs (n ⫽ 10) Göttingen minipigs (n ⫽ 10)
Mandible (transport disc) Mandible (transport disc) Mandible Rabbits (n ⫽ 6)
Infinity
9
Mandible New Zealand white rabbits (n ⫽ 20)
Infinity
1.2
Mandible New Zealand white rabbits (n ⫽ 5)
Infinity
11
11.23 Mandible (anterior) Sheep (n ⫽ 8)
Every 60-120 min 8 increments/s
12 Every 6 min Mandible Göttingen minipigs (n ⫽ 3)
Motor (lithium battery) Motor (lithium battery) Motor (lithium battery) Spring (nickeltitanium) Spring (nickeltitanium) Spring (nickeltitanium) Hydraulic Hannover, Germany Vienna, Austria Schmelzeisen et al, 199620 Ploder et al, 199921,22 1
Location Author Device
Table 1. SUMMARY OF REVIEWED DEVICES
Device Type
Study Model
Site
Rhythm
Average Distraction (mm)
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cessed through a submandibular incision and the distractor was fixed across an osteotomy. The controller was buried in a subcutaneous pocket and sutured to the sternocleidomastoid muscle. After a 5-day latency period, the investigators transcutaneously activated the device. The active distraction period lasted 14 days, followed by neutral fixation for 6 to 7 weeks. Distraction occurred at 0.04 mm/hour, for 1 mm of distraction per day. Clinically, all animals showed unilateral cross-bites and stable mandibles at sacrifice. The length of distraction ranged from 1.7 to 17.1 mm (active distraction range, 2 to 17 days) as measured on the specimens and the device. Radiographically, the gap appeared radiolucent during distraction and slightly radiodense after 5 weeks of fixation. Histologically, a spherical callus developed around the gap and consisted of an irregular fibrous zone between areas of membranous and/or cartilaginous woven bone at the native bone edge. Various size islands of fibro- and hyaline cartilage were seen on the lingual side of the callus, where the periosteum was left intact. This may be a sign of instability. Most recently, Zheng et al23 studied another motordriven distractor in 5 adult New Zealand white rabbits (3 to 3.8 kg). Unilateral vertical mandibular osteotomies were made immediately anterior to the first premolar (Fig 3). The distractors were fixed to the mandible perpendicular to the osteotomy. After a 3-day latency period, an automatic driver fixed on a plastic collar was attached to the distractor and activated 8 steps per second for a total rate of 2 revolutions (0.9 mm) per day. Active distraction continued for 11 days, followed by a 4-week consolidation period. Clinically, all rabbits developed a severe crossbite and overgrowth of incisors and all reached the planned advancement. Radiographically, the osteotomy side showed bony continuity and with bone fill in the gap that was less radiodense than the host bone. Microcomputed tomography demonstrated partial corticalization across the gap. Histologically, a mixture of woven and mature lamellar bone with rich fibrovascular stroma was seen. SPRING-MEDIATED
In 2003 Mofid et al24 studied spring-mediated mandibular DO devices in 20 adult New Zealand white rabbits (4 kg). Their device consisted of a 55-mm-long nickel-titanium alloy bent into an arc shape, reinforced at both ends with pinballs, and secured to the mandible with stainless steel wires (Fig 4). To prevent activation during the 12-day latency phase, the researchers left a second stainless steel wire connecting the pinballs to each other; they reopened the incision to sever this wire when beginning active distraction. Five animals were removed from the study because of infection, nonunion, or device failure. A lateral radio-
410
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FIGURE 1. Motor-driven device with stainless steel plates on the lingual side of the mandible after a 13-mm distraction. Reprinted from Schmelzeisen R, Neumann G, von der Fecht R: Distraction osteogenesis in the mandible with a motor-driven plate: A preliminary animal study. Br J Oral Maxillofac Surg 34:377, 1996 with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
graph was used to show a mean length of the distraction gap of 1.2 mm, with a maximum of 3.7 mm, after 6 weeks of distraction. Histologic examination showed complete bone bridging with no cartilage or
fibrous tissue in all but 1 specimen. At the native bone-callus junction, the remodeled regenerate was distinct but looked similar to native bone. Although the quality of new bone compared well with that
FIGURE 2. Distraction system consisting of a titanium-encased motor and a separate controller placed on the mandible of an animal skull and shown in a lengthened position (arrow). Reprinted from Ploder O, Mayr W, Schnetz G, et al: Mandibular lengthening with an implanted motor-driven device: Preliminary study in sheep. Br J Oral Maxifac 37:274, 1999, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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FIGURE 3. A, Automated system comprised of a driving unit (A), flexible shaft (B), and mounting mechanism (C). The torque generated by the driving unit is transmitted to the activation rod of a distractor (D) through the flexible shaft and mounting mechanism. B, The driving unit (A) is fixed on a plastic collar and connected by a flexible shaft (B) to an external distractor (C) placed on the rabbit mandible. Reprinted from Zheng LW, Cheung LK, Ma L, et al: High-rhythm automatic driver for bone traction: An experimental study in rabbits. Int J Oral Maxillofac Surg 37:737, 2008, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
from traditional distraction methods, the force of this device proved insufficient to produce a clinically significant bone lengthening. Idelsohn et al25 designed another nickel-titanium alloy device to study mandibular transport DO in 6 female rabbits (12 months old, 3 kg). They performed an 8-mm segmental mandibulectomy at the mandibu-
lar body and a corticotomy 5 mm distal to the gap. After a 5-day latency period, they placed commercially available nickel-titanium orthodontic springs between the proximal mandible and the transport segment and left these in place for 2 months (Fig 5). Clinical continuity and normal dimensions were observed in all specimens. Radiographically, 2 to 5 mm
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FIGURE 4. Shape memory alloy spring-distractor model. A 55-mm segment of nitinol secured at either end with a pinball is bent into an inferiorly based arc and secured to the hemimandible with stainless steel wire. Reprinted from Mofid MM, Inoue N, Tufaro AP, et al: Spring-mediated mandibular distraction osteogenesis. J Craniofac Surg 14:757, 2003, with permission from Mutaz B. Habal, MD. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
of lengthening was achieved after 1 week of distraction, and 7 to 13 mm by 3 weeks. Histologically, the trabeculae were oriented longitudinally after the direction of the distraction force. Cells typical of intramembranous ossification were observed, ie, mesenchymal tissue with large numbers of osteoblasts starting to be surrounded by bone lacunas with no sign of cartilage. Zhou et al26 also tested a fully buried, nickel-titanium spring to lengthen the mandibular ramus of 20 New Zealand white male rabbits (6 months old, 3 kg; Fig 6). Four were used as controls. Using a submandibular incision, the ascending ramus and condyle (15-mm segment) were resected by transverse osteotomy, and a transport disc was created in the remnant ramus by L-shaped osteotomy. Six rabbits were sacrificed after 6 days. In these animals the overall rate of distraction slowly decreased with each day of activation: 4 mm on the first day, 2 mm on the second day, 1 mm on the third day, 1.5 mm on the fourth day, 0.5 mm on the fifth day, and 0 mm on the sixth day. The other animals were sacrificed after an 8-week consolidation period. Clinically, no infections occurred and the junction between the new and old bone was
MANDIBULAR DISTRACTION OSTEOGENESIS
morphologically indistinguishable. Radiographically, ossification was documented and the trabeculae were oriented parallel to the ascending ramus. Histologically, longitudinally oriented trabecular bone with regularly arranged collagen bundles was observed. Occasional cartilage was also seen. In 2006 the same group tested this spring-loaded device in 10 hybrid dogs (3 years old, 20 to 25 kg).27 A 40-mm segmental mandibulectomy was made through a submandibular incision from the fourth premolar to the first molar. A second osteotomy was made between the second and third premolars, creating a tooth-bearing transport disc. Distraction began immediately and continued for 28 days when the transport disc reached the proximal segment. The rate of movement began at 3 mm/d and decreased to 1 to 1.5 mm on the following days. After a 12-week consolidation period, the animals were sacrificed. In all animals, the entire defect filled in with new bone that appeared ossified radiographically and was continuous with the native mandible. On histology, new bone trabeculae were organized longitudinally on the distraction side and crosswise on the compression side. HYDRAULIC
Various researchers have used hydraulic forces to drive distractors. Kessler et al28 and Wiltfang et al29 tested a hydraulic device in 6 female Göttingen minipigs. After performing a mandibular osteotomy, they fixed a 9-mm diameter steel cylinder and piston to the proximal and distal segments of the mandible (Fig 7). A flexible
FIGURE 5. Novel superelastic shape memory alloy distractor, showing shape memory alloy springs (S), bone plates to fix the mandible and not allow movements (P), segment that is going to be displaced forward (B), and newly formed bone (C). Reprinted from Idelsohn S, Pena J, Lacroix D, et al: Continuous mandibular distraction osteogenesis using superelastic SMA. J Mater Sci Mater Med 15:542, 2004 (Figure 4) with kind permission from Springer Science and Business Media. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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413 tube connected the internal distractor to an external steering unit on the animal’s back. The unit held a noncompressible fluid kept under constant pressure by a fluid reservoir. After a 7-day latency period, they distracted the mandibles 1.5 mm/d for 8 to 10 days, resulting in 14 to 15 mm of new bone formation. The device was activated manually for discontinuous DO in some animals and continuously using pressure control in others. During the fixation phase, a connectable pressure receptor could be attached to measure the daily pressures. Compared with intermittent distraction, where high pressure peaked immediately after activation and fluctuated with low pressure 2 to 3 hours later, pressure remained at a constant moderate level with continuous distraction. Ultrasound and histologic examinations in the 2 groups showed a central fibrous zone that was poorly mineralized with longitudinally oriented collagen bundles. During fixation, the fibrous zone ossified and woven bone regenerated. There was rare cartilage found. However, in the continuous group, the bone was more ossified on the ultrasound image and more mature on the scanning electron microscopic image. In 2001 a group in Glasgow designed another automatic mandibular distractor using hydraulics.30,31 A tube connected identical internal and external nickel bellows, so compression of the external bellow caused extension of the implanted bellow. A batterydriven portable pump compressed the external bellows, forcing fluid through the connecting tube into the internal component (Fig 8). The movement of the external drive system corresponded with the bone distraction, eliminating the need for radiographs. The investigators tested this device in 11 sheep (24 months old, 55 kg). Three were controls and 8 under-
FIGURE 6. A, Nitinol spring distraction device. Top, Sites of osteotomy. Middle, Removed segment. Bottom, Fixation of the nitinol spring and other devices. Reprinted from Zhou HZ, Hu M, Hu KJ, et al: Transport distraction osteogenesis using nitinol spring: An exploration in canine mandible. J Craniofac Surg 7:944, 2006, with permission from Mutaz B. Habal, MD. B, Radiograph of the reconstructed mandibular ramus using nitinol spring transport distraction osteogenesis. Reprinted from Zhou HZ, Hu M, Yao J, et al: Transport distraction osteogenesis using nitinol spring: An exploration in canine mandible. J Craniofac Surg 15:727, 2004, with permission from Mutaz B. Habal, MD. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
FIGURE 7. Microhydraulic distractor in situ on a pig’s mandible. Reprinted from Wiltfang J, Kessler P, Merten H-A, et al: Continuous and intermittent bone distraction using a microhydraulic cylinder: An experimental study in minipigs. Br J Oral Maxillofac Surg 39:3, 2001, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
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MANDIBULAR DISTRACTION OSTEOGENESIS
FIGURE 8. A, Immediate postoperative lateral oblique radiograph showing the surgical defect in a sheep. Reprinted from Ayoub AF, Richardson W: A new device for microincremental automatic distraction osteogenesis. Br J Oral Maxillofac Surg 39:359, 2001, with permission from Elsevier. B, Panoramic radiograph showing correction of facial asymmetry and the chin in the center of the face. Reprinted from Ayoub AF, Richardson W, Barbenel JC: Mandibular elongation by automatic distraction osteogenesis: The first application in humans. Br J Maxillofac Surg 43:326, 2005, with permission from Elsevier. C, In the sheep model, the internal component of the distraction device was fixed to the proximal segment of the mandible and to the transport disc using 3 bicortical screws at each site. Reprinted from Ayoub AF, Richardson W: A new device for microincremental automatic distraction osteogenesis. Br J Oral Maxillofac Surg 39:357, 2001, with permission from Elsevier. D, The distractor connected by a flexible drive cable, which was passed through a skin incision at the angle of the mandible, to an external plunger mounted in an ambulatory infusion pump. Reprinted from Ayoub AF, Richardson W, Barbenel JC: Mandibular elongation by automatic distraction osteogenesis: The first application in humans. Br J Oral Maxillofac Surg 43:326, 2005, with permission from Elsevier. Goldwaser et al. Mandibular Distraction Osteogenesis. J Oral Maxillofac Surg 2012.
went active distraction. Two of the 8 were excluded because of postoperative complications. A submandibular incision was used to access the mandibular body. A 25-mm segmental mandibulectomy was performed and a 20-mm tooth-bearing transport disc was made posterior to the defect. After a 1-day latency period, the device was activated to distract the transport disc 1 mm divided into 10 steps over 24 hours for 25 days. After an 8-week consolidation period, the animals were sacrificed. Bone formed on the tension
and compression sides; the disc moved 15 mm, resulting in 15 mm of new bone formation on the tension side and 10 mm on the compression side. There was clinical continuity of the regenerated and native bone, with normal morphology. Four animals had infections. Radiographically, the areas anterior and posterior to the transport disc were less radiodense at 2 weeks and became more radiopaque over time. At 8 weeks, the new bone and the transport disc had similar densities. On ultrasound, after 8
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weeks of consolidation, dense bands of calcified tissue were appreciated that looked similar to adjacent bone. Angiography performed before sacrifice showed the inferior alveolar artery and a substantial plexus of small vessels around the regenerate filled with contrast material. Histologically, the regenerate showed haversian systems of mature lamellar bone. The same research group published a case report in 2005 describing the successful use of this device to correct mandibular asymmetry in a 65-year-old man.32
Discussion When designing any new device, it is essential to identify and evaluate specific parameters that can be used as objective markers of success and failure. We have identified the following key features of a clinically useful distraction device whether continuous and/or automated or manual and discontinuous: small size; easily implantable; fully buried; biocompatible; sufficient force generation and maintenance; ability to measure force used; robust enough to withstand in vivo environments; simple design and activation; adjustability of rate, rhythm, and vector once treatment begins; automated with little patient involvement; predictability of distraction endpoint; ability to noninvasively and accurately measure progress of lengthening; need for few additional procedures after implantation. Although currently available and widely used distractors produce predictably successful results, significant problems remain, including size constraints, patient compliance issues, limitation of rate to 1 mm/d, durability issues, inability to measure actual forces of distraction, need for repeated radiation exposure to measure progress, a second procedure to remove the device, infection, and psychosocial effects from external parts. The motor-driven devices reviewed in this article address some of these issues. Two devices were fully buried and automatic and generated sufficient force to move the fragments.20-22 However, neither device consistently distracted 1 mm/d as intended.20,21 The third motor-driven device had an external driver, but this could be removed after the period of active distraction. In this case, distraction occurred as planned.23 None of the motorized device allowed the clinician to measure progress without taking radiographs, and only the third device allowed the clinician to adjust rate, rhythm, or direction once treatment began. The use of implanted motors running on battery power would require invasive procedures to change batteries or fix technical malfunctions, a likely requirement considering the motors’ complexity.20-22 This highlights the benefit of the device of Zheng et al,23 which keeps the driver external and removable.
415 In this review, 3 different spring-mediated devices were presented. The popularity of using springs to generate force stems from the simplicity of design, low cost, and commercial availability of materials. However, although spring devices are self-operating, their force is at a maximum early in distraction, when the spring is fully compressed, but gradually decreases as the spring expands. This is especially detrimental because the amount of force needed to distract increases over time. The finding in 2 springdevice studies that the distraction rate began at 3 to 4 mm/d and gradually decreased in rate over the following days illustrates this point.26,27 Furthermore, although each spring has a unique elasticity curve, spring devices do not offer the ability to control the motion of the segments (ie, rate and rhythm) or to adjust the force based on individual tissue resistance, making it difficult to predict the distraction endpoint.24,27 Directionality is also difficult to predict; most devices described only distracted linearly, although 1 model did use multidirectional vectors.24 The protocol cannot be adjusted without replacing the spring or removing it, and reversal is impossible. Two groups using spring-mediated devices demonstrated transport disc distraction only. It is therefore unclear whether similar results would occur in monofocal distraction. Although all spring designs were fully buried, infection was decreased but not completely eliminated.24,25,27 Two devices required a second incision to activate if the clinician desired a latency period, which added additional surgical risk.24,25 Interestingly, the spring devices shed light on the potential for faster distraction rates with continuous DO, because the investigators found no evidence of fibrous union with a rate of 2 or 4 mm/d with no latency period during the first part of treatment.26,27 This finding supports Ilizarov’s postulation that continuous DO would allow a faster rate.15 The 2 hydraulic distractors reviewed showed significant potential for further development. The 2 devices functioned automatically and required no daily intervention. One design could be used continuously or discontinuously, and the surgeon could interact with the system to adjust the protocol mid treatment.30 An important advantage of the device described by Kessler et al28 is its ability to measure the force applied to the segments, a valuable feature for future technical development and miniaturization of distractors. Nevetheless, the pressure sensor was somewhat removed from the actual site of the distractor and may not prove accurate. In addition, the 2 devices were semiburied with a tube exiting at the neck that may have caused some of the encountered infections.28,31 One of the hydraulic devices had the additional benefit of being able to measure the distance distracted without radiographs, and although
416 not in widespread use, this group has shown future potential with its case report of application in a human adult.30-32 The abundance of research currently under way to develop a continuous distractor highlights the clinical demand for and usefulness of such a device. Despite the promising results of many groups, significant challenges remain to be overcome before any of these devices gain broad clinical acceptance. Issues of infection, external scars, psychosocial stress, measurement of distractor gap without radiation, mid-course protocol adjustability, curvilinear distraction, size of device, and the need for multiple procedures must still be resolved. Thus, significant work remains. In an effort to improve existing discontinuous distractors and continuous distractors in development, the present investigators are working on a novel, buried, hydraulic, automated, continuous, curvilinear mandibular distractor (National Institute of Health, Small Business Innovation Research Grant 5R44 DE 01480303).33 The results of this project will be submitted in a subsequent report.
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