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Distraction osteogenesis after membranous bone onlay grafting in a dog model
SCIENTIFIC ARTICLES J Oral Maxillofac Surg 59:1025-1033, 2001
Distraction Osteogenesis After Membranous Bone Onlay Grafting in a Dog Model Byung Chae Cho, MD,* Man Soo Seo, MD,† and Bong Soo Baik, MD‡ Purpose:
The purpose of this experiment was to study the possibility of distraction osteogenesis in a membranous bone onlay graft to the mandible and to clarify the histology of the bone repair. Materials and Methods: Four dogs, 5 months of age at the beginning of the experiment, were used for this study. The zygomatic arch was exposed in the subperiosteal plane, and a 3-cm long, full-thickness portion of the arch was harvested. The lateral surface of the mandibular body was exposed in the subperiosteal plane, and the bone was fixed to the lateral surface as a membranous onlay graft using screws. A vertical osteotomy through the graft and underlying mandibular body was done postoperatively at week 1 in dog 1, week 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. An external distraction device was applied to the mandibular body, and distraction was started 7 days after the operation at a rate of 1 mm/d for 10 days. After completion of distraction, the device was left in place for 6 weeks to allow for bony consolidation. Radiographs were carried out at 2, 4, and 6 weeks postdistraction. All dogs were killed 6 weeks after distraction. Results: New bone between the native underlying mandibular segments was generated in the distraction zone in all dogs. New bone was not generated between the segments of the membranous bone onlay graft in dog 1, but was generated in dog 2, dog 3, and dog 4. However, in dogs 2 and 3, the new bone between the segments was less firm, with more fibrous tissue, than the bone between the native underlying mandibular segments. Histologically, the distraction gap between the segments of the membranous bone onlay graft in dogs 2 and 3 was composed of considerable fibrous tissue in the central zone and activated osteoblastic cells forming new bone in the margins. In dog 4, there was much more osteoblastic activity in the distraction gap, and the new bone had the appearance of almost normal cortical bone. Conclusion: These findings show that distraction osteogenesis is possible in a membranous bone onlay graft and suggest that the distraction should be performed at least 4 weeks after the onlay grafting. © 2001 American Association of Oral and Maxillofacial Surgeons In 1992, McCarthy et al1 introduced the use of distraction osteogenesis to lengthen the human mandible. Subsequently, many reports have appeared in Received from the Department of Plastic and Reconstructive Surgery, Kyungpook National University Hospital, Taegu, Korea. *Associate Professor and Chief. †Staff, Patima Hospital. ‡Professor. Address correspondence and reprint requests to Dr Cho: Department of Plastic and Reconstructive Surgery, Kyungpook National University Hospital, Samduk 2 ga 50, Taegu, 700-721, Korea; e-mail: [email protected] © 2001 American Association of Oral and Maxillofacial Surgeons
0278-2391/01/5909-0010$35.00/0 doi:10.1053/joms.2001.25831
literature.2-22 However, several authors have reported that the distracted region in patients with severe mandibular hypoplasia did not have enough bone tissue bulk on the lateral surface of the distracted mandible. Kocabalkan et al13 and Havlik and Bartlett14 did repeated mandibular lengthening in Treacher Collins syndrome and hemifacial microsomia patients. Corcoran et al21 reported a series of 8 patients undergoing distraction osteogenesis of neomandibles constructed with costochondral grafts, and Polley et al19 reported simultaneous distraction osteogenesis of the mandible and a vascularized scapular bone flap in severe hemifacial microsomia. It has been known that a free membranous bone graft has a high survival rate in young patients with mandibular defects and produces new bone. Several
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authors23-38 have reported that the survival of onlay membranous bone grafts was greater than that of endochondral bone, showing early vascular ingrowth at 3 days, good vascularization at 7 days, and complete vascularization at 14 days. The following questions were specifically addressed in this study: 1) is bone formation possible during distraction osteogenesis of a free membranous bone onlay graft; 2) are there histologic differences in the distraction osteogenesis site in a free membranous bone onlay graft and normal bone; and 3) how soon after membranous bone onlay grafting is distraction possible? An understanding of bone formation during distraction osteogenesis of a membranous bone onlay graft to the mandible could help shorten the treatment period for cases of severe mandibular hypoplasia that require both a bone graft and distraction. FIGURE 2. Lateral view after the vertical osteotomy.
Material and Methods Four dogs, 5 months of age at the beginning of the experiment, were used for this study. Each dog was subjected to endotracheal intubation and general anesthesia, and standard facial sterilization preparation and draping were done. Infiltration of 1% lidocaine with 1:200,000 epinephrine was used for hemostasis during the free membranous bone onlay graft placement. A 5-cm skin incision along the zygomatic arch was carried down to the bone, the masseter muscle was reflected, and the zygomatic arch was exposed in the subperiosteal plane. A full-thickness segment of the zygomatic arch, 2 to 3 cm in length, was harvested. Then, a 4 to 5 cm longitudinal skin incision along the inferior border of
FIGURE 1. Membranous bone, 3 cm in length, harvested from the zygomatic arch and fixed on the inferior lateral part of the mandibular body.
the mandible was carried down to the mandibular body, the masseter muscle was reflected, and the lateral surface of the mandible was exposed in the subperiosteal plane. The membranous bone graft was placed in a subperiosteal pocket with firm bone-tobone contact using screws (Fig 1), and the wound was then closed in layers. The osteotomy in the free membranous onlay bone and the underlying mandibular body was made at week 1 postoperatively in dog 1, week 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. A 3-cm vertical incision was made in the skin over the bone graft and mandibular body. Minimal soft tissue dissection was done over the graft so as not to impair the blood supply. A vertical osteotomy was made in the center of the bone graft and outer cortex of underlying mandibular body with a powered sagittal saw (Fig 2). A greenstick fracture of the inner cancellous portion was made using an osteotome, maintaining the continuity of the inferior alveolar neurovascular bundle. Two bicortical pins, 3 mm in diameter, were introduced percutaneously approximately 20 mm from each other, and the external distraction device (Molina distractors; Wells Johnson Company, Mexico City, Mexico) was then applied. All dogs were given 500,000 U aqueous penicillin during surgery. Routine wound care was given, as well as intramuscular injections of penicillin (0.1 mL 10,000 U/kg) every 6 hours for 7 days. A soft diet was provided immediately after the surgical procedures and until day 3, when a general diet was started. After 7 days for wound healing, mandibular distraction was started using a customized wrench at a rate of 1 mm/d for a total of 10 mm. On completion of the distraction, the device was left in place for 6 weeks to allow for bony consolidation (Fig 3). The dogs were
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then stained with hematoxylin and eosin for microscopic examination.
Results GROSS OBSERVATIONS
FIGURE 3. Lateral view after complete distraction.
killed by giving an overdose of pentobarbital (40 to 50 mg/kg). Radiographs were made at 2, 4, and 6 weeks postdistraction. Longitudinal specimens of the lengthened part of the mandible and the adjacent normal bone were obtained using a saw. The resected mandible was placed in 10% neutral buffered formalin for 1 week. After fixation, the specimens were decalcified in 10% nitric acid and 10% sodium citrate for 48 hours. After decalcification, the distracted region was sectioned with a scalpel and washed to remove excessive fixative and then dehydrated by passing it through increasing strengths of ethyl alcohol. The sections were
All dogs recovered satisfactorily, and the distraction device was well tolerated. The appliance was cleaned daily during the expansion. New bone between the distracted native mandibular segments was seen in all dogs. The gain in length was 8 mm in dog 1, 7 mm in dog 2, 6 mm in dog 3, and 8 mm in dog 4. In dog 1, the membranous bone onlay graft was partially resorbed, and new bone was not generated between the segments. However, in dogs 2 and 3, new bone had formed along the edges of the distracted segments, but the firmness in the distracted area was less than that of underlying mandibular segment (Fig 4). In dog 4, there was partial resorption of the membranous bone onlay graft near the pin fixation region because of inflammation. However, much new bone with a nearly normal cortical appearance had formed between the segments (Fig 5). RADIOGRAPHS
Serial postoperative radiographs showed progressive calcification in the distraction zone in the native
FIGURE 4. Macroscopic appearance of a distracted bone in dog 2 (osteotomy 2 weeks after membranous bone onlay graft) and dog 3 (osteotomy 3 weeks after membranous bone onlay graft). A, dog 2, lateral view. B, dog 2, ventral view. C, dog 3, lateral view. D, dog 3, ventral view. The arrows indicate new bone formation in the distracted region of the membranous bone onlay graft.
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Partially calcified, irregularly shaped woven bone trabeculae and variable-sized new blood vessels were mixed in the distraction region. Immature woven bone trabeculae and a small number of cartilage islands were seen at the edge of the distraction zone (Fig 8). There was new periosteal bone formation on the medial surface of the mandible. There was no new bone formation in the distracted region in the membranous bone onlay graft in dog 1. In dog 2, the distracted region was almost bridged by fibrous tissue. Osteogenesis was seen, and abundant active osteoblasts were forming woven bone at the edge of the distracted area. In dog 3, the distracted region was filled with new bone and fibrous tissue. Abundant osteoblasts and woven bone were seen at the edges of the distracted region (Fig 9). However, in dog 4, there was considerable woven bone in the entire distraction zone and a narrow fibrous interzone (Fig 10). The new bone appeared almost like normal cortex (Fig 10A).
Discussion FIGURE 5. Macroscopic appearance of the distracted bone in dog 4 (osteotomy 4 weeks after membranous bone onlay graft). A, Lateral view. B, Ventral view. The arrows indicate new bone formation in the distracted region of the membranous bone onlay graft. Bone resorption is noted at the pin fixation region in A.
mandibular segment in all dogs. This was comprised of a proximal and distal sclerotic zone sandwiching a central radiolucent zone. There was no radiodense region in the distraction zone of the membranous bone onlay graft in dog 1. In dogs 2 and 3, there were small radiodense regions in the edge of the distraction zone of the membranous bone onlay graft. In dog 4, the full thickness of the distracted site in both the membranous bone onlay graft and the underlying mandibular segment showed zones of ossification proximally and distally, with a radiolucent central zone. By 6 weeks, the new bone became progressively radiodense and extended into the center of the distraction zone (Fig 6). HISTOLOGIC FINDINGS
The membranous bone onlay graft showed normal osteoblastic activity, and the bony architecture was similar to the underlying mandible (Fig 7). Under a magnification of 200, the number of viable vessels were 10 in the membranous bone onlay graft and 11 in the underlying mandible. These findings suggest that vascularization of the membraneous bone onlay graft returned to nearly normal. Extensive fibrosis and proliferation of many osteoblasts forming osteoid were seen in the central region of the distracted zone in the underlying mandible.
In a serial histologic study using dogs, Karp et al39 divided the bony regenerate into 4 zones of healing: 1) a fibrous central zone, 2) a transition zone of early bone formation, 3) a bone remodeling zone of early bone formation, and 4) a zone of mature bone. They suggested that the primary mechanism of bone formation in the mandible was predominantly by intramembranous ossification, with a gradient of mineralization from a central fibrous interzone. Califano et al4 described the histologic development of the bony regenerate in 3 phases: 1) a colloidal phase (after 2 weeks), 2) a fibrillar phase (after 5 weeks), and 3) a lamellar phase (after 8 weeks). These experimental results showed that distraction osteogenesis induced new bone formation in the maxillofacial complex by direct mesenchymal induction rather than by cartilage formation, as in the long bones. Kumuro et al8 reported that the new bone produced by distraction osteogenesis was formed by both intramembranous and endochondral ossification. Endochondral bone healing also has been reported in mandibular experimental models.4,6,7 However, most authors believe that cartilage formation is a sign of either low oxygen tension or micromovement of the regenerate caused by instability during osteodistraction. Recently, Mehrara et al22 Showed that transforming growth factor-1 production may be an important regulator of vasculogenesis and that osteocalcin gene expression coincides temporally with mineralization during rat mandibular distraction osteogenesis. Our microscopic observations confirmed that the greater portion of new bone in the distracted region of normal mandible and in the mem-
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FIGURE 6. Ventral radiographs at 6 weeks after distraction. A, Dog 1. The arrow indicates a radiolucent region at the edge of the distracted region between the membranous bone onlay graft. B, Dog 3. C, Dog 4. The new bone is radiodense.
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FIGURE 7. Histologic section of the membranous bone onlay graft. There are many active osteoblasts and blood vessels (arrows) in the lacunae (hematoxylin & eosin stain, original magnification ⫻200).
branous bone onlay graft was generated by intramembranous bone formation. Cartilage formation only filled a small portion of the distraction gap. The gain in length ranged from 6 to 8 mm, yet the device was activated 10 mm. These results can be explained by convergence of the distraction vector in the device used. To have exact activated length, use
DISTRACTION OSTEOGENESIS
of 4 pins or an intraoral device to transmit the activation length to the distraction region is recommended. Havlik and Bartlett14 and Klein and Howaldt15 confirmed that protection of the periosteum does not seem to be necessary in mandibular distraction in children. Because of its rich blood supply, the craniofacial skeleton, can tolerate a more liberal elevation of the periosteum and a complete osteotomy. Knize et al23 observed enhanced survival of nonvascularized bone grafts with retained periosteum. They suggested that the periosteum provides a surviving population of osteogenic cells and a route for earlier revascularization of the bone graft. Thompson and Casson24 postulated that the periosteum aided the process of circulatory reanastomosis. Ozerdem et al40 showed the possibility of distraction osteogenesis in periosteal bone grafts and provided information regarding the importance of the periosteum and its osteogenic capacity. We did not include periosteum with the membranous bone onlay graft. In dog 1 and dog 4, the membranous bone onlay graft showed partial resorption caused by inflammation. We believe that if the membranous bone onlay graft had retained its periosteum this would have prevented the resorption and enhanced earlier revascularization.
FIGURE 8. Histologic section of the mandible of dog 1 at 6 weeks after distraction. A, The distracted region in the underlying mandible is almost fully bridged by new bone, leaving a small fibrous interzone (hematoxylin & eosin stain, original magnification ⫻5). Arrows indicate the distraction gap. B, A small number of cartilage islands and immature woven bone are seen (hematoxylin & eosin stain, original magnification ⫻40).
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FIGURE 9. Histologic section of the membranous bone onlay graft and underlying mandible in dog 2 at 6 weeks after distraction. A, The distracted region of the membranous onlay bone graft is almost bridged by fibrous tissue. Osteogenesis (arrow) is seen at the edges of the distracted area (hematoxylin & eosin stain, original magnification ⫻5). B, Schematic diagram of histologic section. A, membranous bone onlay graft; B, normal mandibular body; C, osteogenesis at the edge of the distracted region; D, fibrous interzone; E, new bone formation by periosteal reaction on the medial surface. C, High power view showing abundant active osteoblasts forming woven bone at the edges of the distracted region of the membranous bone onlay graft (hematoxylin & eosin stain, original magnification ⫻40).
FIGURE 10. Histologic section of the membranous bone onlay graft in dog 4 at 6 weeks after distraction. The underlying mandible and its distracted region were removed. A, The distracted region of the membranous bone onlay graft (arrow) is almost filled with woven bone (hematoxylin & eosin stain, original magnification ⫻10). B, Schematic diagram of histologic section. A, membranous bone onlay graft; B, woven bone in the distracted region; C, narrow fibrous interzone. C, Magnification of the distracted region of the membranous bone onlay graft. Woven bone (A) and islands of cartilage (B) are seen (hematoxylin & eosin stain, original magnification ⫻100).
1032 Numerous factors act to influence bone graft survival. Early revascularization is thought to be the most important factor for a successful graft. Cutting and McCarthy,25 La Trenta et al,26 and Antonyshyn et al27 all showed that vascularized membranous bone grafts in the immature dog model retain the normal architecture, with minimal resorption and considerable subperiosteal callus formation, and that they continue to grow. Although it has been recognized that vascularized bone transfers are superior in the growing child, vascularized bone transfers are technically much more difficult to harvest and shape and also there are limited donor sites. In the majority of instances in craniofacial reconstruction in the growing child, nonvascularized membranous bone onlay grafts may be preferable. Rigid fixation techniques and high oxygen tension in the healing environment have been shown to aid in the primary repair of membranous bone.32 Phillips and Rahn35 emphasized that bone resorption predominated in the presence of movement in regions with intermittent contact or poor fixation. They noted that membranous bone showed greater revascularization at 2 weeks when fixed than when not fixed. The stability of the fixation during the entire distraction procedure may be important, not only in relation to the recovery of vascularity but also to the cellular response. Smith and Abramson,30 Zins and Whitaker,31 and Kuziak et al32 showed that nonvascularized membranous bone grafts undergo less resorption than endochondral bone grafts in animal models. They suggested that the increased volume of the membranous bone graft was most likely caused by either more rapid revascularization, and hence greater graft survival, or delayed revascularization and hence delayed bone graft resorption. Endochondral bone grafts are believed to be more susceptible to resorption because of the less dense structure of the trabeculae. Wilkes et al33 studied the survival of onlay bone grafts in mature and immature animals and found that membranous bone survived twice as well as endochondral bone. Ozaki and Buchman38 reported that cortical bone grafts maintain their volume significantly better than cancellous bone grafts, and they believed cortical bone to be a superior onlay grafting material, independent of its embryologic origin. In our study, we used the zygomatic arch as a donor site because it is easy to harvest and because it shortens the operation time. However, it is rare for the zygomatic arch to be used as a donor site of the membranous bone clinically. Calvarial bone is the ideal graft choice and can provide a readily available source for craniofacial reconstruction. We expected vascularization of the membranous bone graft from the neighboring tissues and new
DISTRACTION OSTEOGENESIS
bone formation between membranous bone onlay graft. Our results showed no new bone formation in dog 1, partial new bone formation at the edges of the distraction zone in dog 2 and 3, and nearly normal bone formation in dog 4. Soft tissue dissection for the osteotomy and the osteotomy itself probably affected the revascularization of the membranous bone onlay graft from the neighboring tissues. This delayed revascularization of the graft resulted in initial minimal osteoblastic activity after distraction. We believe that to have new bone formation in a membranous bone onlay graft, distraction should not be done until at least 4 weeks after bone grafting. Kocabalkan et al13 and Havlik and Bartlett14 reported repeated bilateral mandibular lengthening in a patient with a severely hypoplastic mandible. Roth et al20 did a quantitative volumetric assessment of the mandible after distraction osteogenesis using computed tomography scans and reported a mean increase of 27% in the distracted hemimandible and 25% in the bilaterally distracted mandibles. Even though the soft tissue and bony volume was increased after distraction, occasionally the increased volume was not enough to correct the severe hypoplasia of the facial bones. Polley et al19 believed that skeletal reconstruction in patients with severe craniofacial microsomia should be performed with a combination of distraction osteogenesis of the mandible and free vascularized scapula bone grafts. The bone graft was distracted along with the native mandibular ramus. Corcoran et al21 reported 8 patients with craniofacial microsomia who had undergone costochondral rib graft reconstruction of the ramus (average 5.1 years earlier) and then had been submitted successfully to distraction osteogenesis to lengthen the deficient mandible. They also showed that the previous osteotomy sites were also amenable to distraction and that previously distracted mandibles could undergo successful sagittal split osteotomies. It was generally postulated that it is safe to perform distraction of a membranous bone onlay graft 6 months or more after placement. There are no exact data regarding the earliest time for distraction of the membranous bone onlay graft in patients with severe hemifacial microsomia. Our results show that distraction osteogenesis in a membranous bone onlay graft is possible in dog model at 4 weeks. However, clinical evaluation is necessary.
References 1. McCarthy JG, Schreiber J, Karp N, et al: Lengthening the human mandible by gradual distraction. Plast Reconstr Surg 89:1, 1992 2. Karaharju-Suvanto T, Peltonen J, Kahri A, et al: Distraction osteogenesis of the mandible. An experimental study on sheep. Int J Oral Maxillofac Surg 21:118, 1992
CHO, SEO, AND BAIK 3. Block MS, Daire J, Stover J, et al: Changes in the inferior alveolar nerve following mandibular lengthening in the dog using distraction osteogenesis. J Oral Maxillofac Surg 51:652, 1993 4. Califano L, Cortese A, Zupi A, et al: Mandibular lengthening by external distraction: An experimental study in the rabbit. J Oral Maxillofac Surg 52:1179, 1994 5. Ganey TM, Klotch DW, Slater-Haase AS, et al: Evaluation of distraction osteogenesis by scanning electron microscopy. Otolaryngol Head Neck Surg 111:265, 1994 6. Guerrissi J, Ferrentino G, Margulies D, et al: Lengthening of the mandible by distraction osteogenesis: Experimental work in rabbits. J Craniofac Surg 5:313, 1994 7. Gantous A, Phillips JH, Catton P, et al: Distraction osteogenesis in the irradiated canine mandible. Plast Reconstr Surg 93:164, 1994 8. Kumuro Y, Takato T, Harii K, et al: The histologic analysis of distraction osteogenesis of the mandible in rabbits. Plast Reconstr Surg 94:152, 1994 9. Klotch DW, Ganey TM, Slater-Haase A, et al: Assessment of bone formation during osteoneogenesis: A canine model. Otolaryngol Head Neck Surg 112:291, 1995 10. Sawaki Y, Ohkubo H, Hibi H, et al: Mandibular lengthening by distraction osteogenesis using osseintegrated implants and an intraoral device: A preliminary report. J Oral Maxillofac Surg 54:594, 1996 11. Block MS, Chang A, Crawford C: Mandibular alveolar ridge augmentation in the dog using distraction osteogenesis. J Oral Maxillofac Surg 54:309, 1996 12. Habal MB: New bone formation by biological rhythmic distraction. J Craniofac Surg 5:344, 1994 13. Kocabalkan O, Leblebicioglu G, Erk Y, et al: Repeated mandibular lengthening in Treacher Collins syndrome: A case report. Int J Oral Maxillofac Surg 24:406, 1995 14. Havlik RJ, Bartlett SP: Mandibular distraction lengthening in the severely hypoplastic mandible: A problematic case with tongue aplasia. J Craniofac Surg 5:305, 1994 15. Klein C, Howaldt HP: Lengthening of the hypoplastic mandible by gradual distraction in childhood—a preliminary report. J Craniomaxillofac Surg 23:68, 1995 16. Pensler JM, Goldberg DP, Lindell B, et al: Skeletal distraction of the hypoplastic mandible. Ann Plast Surg 34:130, 1995 17. McCormick SU, McCarthy JG, Grayson BH, et al: Effect of mandibular distraction on the temporomandibular distraction on the temporomandibular joint: Part 1 canine study. J Craniofac Surg 6:358, 1995 18. Molina F, Ortiz-Monasterio F: Mandibular elongation and remodelling by distraction: A farewell to major osteotomies. Plast Reconstr Surg 96:825, 1995 19. Polley JW, Brecker GL, Ramasastry S, et al: Simultaneous distraction osteogenesis and microsurgical reconstruction for facial asymmetry. J Craniofac Surg 7:469, 1996 20. Roth DA, Gosain AK, McCarthy JG, et al: A CT scan technique for quantitative volumetric assessment of the mandible after distraction osteogenesis. Plast Reconstr Surg 99:1237, 1997 21. Corcoran J, Hubli EH, Salyer KE: Distraction osteogenesis of costochondral neomandibles: A clinical experience. Plast Reconstr Surg 100:311, 1997
1033 22. Mehrara BJ, Rowe NM, Steinbrech DS, et al: Rat mandibular distraction osteogenesis: II. Molecular analysis of transforming growth factor beta-1 and osteocalcin gene expression. Plast Reconstr Surg 103:536, 1999 23. Knize DM, Gerskberg H, Ballantyne DL: Hormonal enhancement of autologous onlay bone grafts. Surg Forum 24:511, 1973 24. Thompson N, Casson JA: Experimental onlay bone grafts to the jaws. A preliminary study in dogs. Plast Reconstr Surg 46:341, 1970 25. Cutting CB, McCarthy JG: Comparison of residual osseous mass between vascularized and nonvascularized onlay bone transfers. Plast Reconstr Surg 72:672, 1983 26. La Trenta GS, McCarthy JG, Cutting CB: The growth of vascularized onlay bone transfer. Ann Plast Surg 18:511, 1987 27. Antonyshyn O, Colcleugh RG, Anderson C: Growth potential in onlay bone grafts: A comparison of vascularized and free calvarial bone and suture bone grafts. Plast Reconstr Surg 79:12, 1987 28. Bartlett SP, Whitaker LA: Growth and survival of vascularized and nonvascularized membranous bone: An experimental study. Plast Reconstr Surg 84:783, 1989 29. Muschler GF, Lane JM: Orthopedic surgery, in Habal MB, Reddi AH (eds): Bone Grafts and Bone Substitutes. Philadelphia, PA, Saunders, 1992, pp 381-382 30. Smith JD, Abramson M: Membranous vs endochondral bone autografts. Arch Otolaryngol Head Neck Surg 99:203, 1974 31. Zins JE, Whitaker LA: Membranous versus endochondral bone: Implications for craniofacial reconstruction. Plast Reconstr Surg 72:778, 1983 32. Kuziak JF, Zins JE, Whitaker LA: The early revascularization of membranous bone graft. Plast Reconstr Surg 76:510, 1985 33. Wilkes GH, Kernahan DA, Christenson M: The long term survival of onlay bone grafts: A comparative study in mature and immature animals. Ann Plast Surg 14:374, 1985 34. Bassett CAL, Herrman I: Influence of oxygen concentration and mechanical factors on differentiation of connective tissue in vitro. Nature 190:460, 1961 35. Phillips JH, Rahn BA: Fixation effects on membranous and endochondral onlay bone graft resorption. Plast Reconstr Surg 82:872, 1988 36. Goldstein JA, Mase CA, Newman MH: The influence of bony architecture on fixed membranous bone graft survival. Ann Plast Surg 34:162, 1995 37. Phillips JH, Rahn BA: Fixation effects on membranous and endochondral onlay bone graft revascularization and bone deposition. Plast Reconstr Surg 85:891, 1990 38. Ozaki W, Buchman SR: Volume maintenance of onlay bone grafts in the craniofacial skeleton: Micro-architecture versus embryologic origin. Plast Reconstr Surg 102:291, 1998 39. Karp NS, McCarthy JG, Schreiber JS, et al: Membranous bone lengthening: A serial histologic study. Ann Plast Surg 29:2, 1992 40. Ozerdem OR, Kivanc O, Tuncer I, et al: Callotasis in nonvascularized periosteal bone grafts and the role of periosteum: A new contribution to the concept of distraction osteogenesis. Ann Plast Surg 41:148, 1998
Distraction Osteogenesis After Membranous Bone Onlay Grafting in a Dog Model Byung Chae Cho, MD,* Man Soo Seo, MD,† and Bong Soo Baik, MD‡ Purpose:
The purpose of this experiment was to study the possibility of distraction osteogenesis in a membranous bone onlay graft to the mandible and to clarify the histology of the bone repair. Materials and Methods: Four dogs, 5 months of age at the beginning of the experiment, were used for this study. The zygomatic arch was exposed in the subperiosteal plane, and a 3-cm long, full-thickness portion of the arch was harvested. The lateral surface of the mandibular body was exposed in the subperiosteal plane, and the bone was fixed to the lateral surface as a membranous onlay graft using screws. A vertical osteotomy through the graft and underlying mandibular body was done postoperatively at week 1 in dog 1, week 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. An external distraction device was applied to the mandibular body, and distraction was started 7 days after the operation at a rate of 1 mm/d for 10 days. After completion of distraction, the device was left in place for 6 weeks to allow for bony consolidation. Radiographs were carried out at 2, 4, and 6 weeks postdistraction. All dogs were killed 6 weeks after distraction. Results: New bone between the native underlying mandibular segments was generated in the distraction zone in all dogs. New bone was not generated between the segments of the membranous bone onlay graft in dog 1, but was generated in dog 2, dog 3, and dog 4. However, in dogs 2 and 3, the new bone between the segments was less firm, with more fibrous tissue, than the bone between the native underlying mandibular segments. Histologically, the distraction gap between the segments of the membranous bone onlay graft in dogs 2 and 3 was composed of considerable fibrous tissue in the central zone and activated osteoblastic cells forming new bone in the margins. In dog 4, there was much more osteoblastic activity in the distraction gap, and the new bone had the appearance of almost normal cortical bone. Conclusion: These findings show that distraction osteogenesis is possible in a membranous bone onlay graft and suggest that the distraction should be performed at least 4 weeks after the onlay grafting. © 2001 American Association of Oral and Maxillofacial Surgeons In 1992, McCarthy et al1 introduced the use of distraction osteogenesis to lengthen the human mandible. Subsequently, many reports have appeared in Received from the Department of Plastic and Reconstructive Surgery, Kyungpook National University Hospital, Taegu, Korea. *Associate Professor and Chief. †Staff, Patima Hospital. ‡Professor. Address correspondence and reprint requests to Dr Cho: Department of Plastic and Reconstructive Surgery, Kyungpook National University Hospital, Samduk 2 ga 50, Taegu, 700-721, Korea; e-mail: [email protected] © 2001 American Association of Oral and Maxillofacial Surgeons
0278-2391/01/5909-0010$35.00/0 doi:10.1053/joms.2001.25831
literature.2-22 However, several authors have reported that the distracted region in patients with severe mandibular hypoplasia did not have enough bone tissue bulk on the lateral surface of the distracted mandible. Kocabalkan et al13 and Havlik and Bartlett14 did repeated mandibular lengthening in Treacher Collins syndrome and hemifacial microsomia patients. Corcoran et al21 reported a series of 8 patients undergoing distraction osteogenesis of neomandibles constructed with costochondral grafts, and Polley et al19 reported simultaneous distraction osteogenesis of the mandible and a vascularized scapular bone flap in severe hemifacial microsomia. It has been known that a free membranous bone graft has a high survival rate in young patients with mandibular defects and produces new bone. Several
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authors23-38 have reported that the survival of onlay membranous bone grafts was greater than that of endochondral bone, showing early vascular ingrowth at 3 days, good vascularization at 7 days, and complete vascularization at 14 days. The following questions were specifically addressed in this study: 1) is bone formation possible during distraction osteogenesis of a free membranous bone onlay graft; 2) are there histologic differences in the distraction osteogenesis site in a free membranous bone onlay graft and normal bone; and 3) how soon after membranous bone onlay grafting is distraction possible? An understanding of bone formation during distraction osteogenesis of a membranous bone onlay graft to the mandible could help shorten the treatment period for cases of severe mandibular hypoplasia that require both a bone graft and distraction. FIGURE 2. Lateral view after the vertical osteotomy.
Material and Methods Four dogs, 5 months of age at the beginning of the experiment, were used for this study. Each dog was subjected to endotracheal intubation and general anesthesia, and standard facial sterilization preparation and draping were done. Infiltration of 1% lidocaine with 1:200,000 epinephrine was used for hemostasis during the free membranous bone onlay graft placement. A 5-cm skin incision along the zygomatic arch was carried down to the bone, the masseter muscle was reflected, and the zygomatic arch was exposed in the subperiosteal plane. A full-thickness segment of the zygomatic arch, 2 to 3 cm in length, was harvested. Then, a 4 to 5 cm longitudinal skin incision along the inferior border of
FIGURE 1. Membranous bone, 3 cm in length, harvested from the zygomatic arch and fixed on the inferior lateral part of the mandibular body.
the mandible was carried down to the mandibular body, the masseter muscle was reflected, and the lateral surface of the mandible was exposed in the subperiosteal plane. The membranous bone graft was placed in a subperiosteal pocket with firm bone-tobone contact using screws (Fig 1), and the wound was then closed in layers. The osteotomy in the free membranous onlay bone and the underlying mandibular body was made at week 1 postoperatively in dog 1, week 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. A 3-cm vertical incision was made in the skin over the bone graft and mandibular body. Minimal soft tissue dissection was done over the graft so as not to impair the blood supply. A vertical osteotomy was made in the center of the bone graft and outer cortex of underlying mandibular body with a powered sagittal saw (Fig 2). A greenstick fracture of the inner cancellous portion was made using an osteotome, maintaining the continuity of the inferior alveolar neurovascular bundle. Two bicortical pins, 3 mm in diameter, were introduced percutaneously approximately 20 mm from each other, and the external distraction device (Molina distractors; Wells Johnson Company, Mexico City, Mexico) was then applied. All dogs were given 500,000 U aqueous penicillin during surgery. Routine wound care was given, as well as intramuscular injections of penicillin (0.1 mL 10,000 U/kg) every 6 hours for 7 days. A soft diet was provided immediately after the surgical procedures and until day 3, when a general diet was started. After 7 days for wound healing, mandibular distraction was started using a customized wrench at a rate of 1 mm/d for a total of 10 mm. On completion of the distraction, the device was left in place for 6 weeks to allow for bony consolidation (Fig 3). The dogs were
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then stained with hematoxylin and eosin for microscopic examination.
Results GROSS OBSERVATIONS
FIGURE 3. Lateral view after complete distraction.
killed by giving an overdose of pentobarbital (40 to 50 mg/kg). Radiographs were made at 2, 4, and 6 weeks postdistraction. Longitudinal specimens of the lengthened part of the mandible and the adjacent normal bone were obtained using a saw. The resected mandible was placed in 10% neutral buffered formalin for 1 week. After fixation, the specimens were decalcified in 10% nitric acid and 10% sodium citrate for 48 hours. After decalcification, the distracted region was sectioned with a scalpel and washed to remove excessive fixative and then dehydrated by passing it through increasing strengths of ethyl alcohol. The sections were
All dogs recovered satisfactorily, and the distraction device was well tolerated. The appliance was cleaned daily during the expansion. New bone between the distracted native mandibular segments was seen in all dogs. The gain in length was 8 mm in dog 1, 7 mm in dog 2, 6 mm in dog 3, and 8 mm in dog 4. In dog 1, the membranous bone onlay graft was partially resorbed, and new bone was not generated between the segments. However, in dogs 2 and 3, new bone had formed along the edges of the distracted segments, but the firmness in the distracted area was less than that of underlying mandibular segment (Fig 4). In dog 4, there was partial resorption of the membranous bone onlay graft near the pin fixation region because of inflammation. However, much new bone with a nearly normal cortical appearance had formed between the segments (Fig 5). RADIOGRAPHS
Serial postoperative radiographs showed progressive calcification in the distraction zone in the native
FIGURE 4. Macroscopic appearance of a distracted bone in dog 2 (osteotomy 2 weeks after membranous bone onlay graft) and dog 3 (osteotomy 3 weeks after membranous bone onlay graft). A, dog 2, lateral view. B, dog 2, ventral view. C, dog 3, lateral view. D, dog 3, ventral view. The arrows indicate new bone formation in the distracted region of the membranous bone onlay graft.
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DISTRACTION OSTEOGENESIS
Partially calcified, irregularly shaped woven bone trabeculae and variable-sized new blood vessels were mixed in the distraction region. Immature woven bone trabeculae and a small number of cartilage islands were seen at the edge of the distraction zone (Fig 8). There was new periosteal bone formation on the medial surface of the mandible. There was no new bone formation in the distracted region in the membranous bone onlay graft in dog 1. In dog 2, the distracted region was almost bridged by fibrous tissue. Osteogenesis was seen, and abundant active osteoblasts were forming woven bone at the edge of the distracted area. In dog 3, the distracted region was filled with new bone and fibrous tissue. Abundant osteoblasts and woven bone were seen at the edges of the distracted region (Fig 9). However, in dog 4, there was considerable woven bone in the entire distraction zone and a narrow fibrous interzone (Fig 10). The new bone appeared almost like normal cortex (Fig 10A).
Discussion FIGURE 5. Macroscopic appearance of the distracted bone in dog 4 (osteotomy 4 weeks after membranous bone onlay graft). A, Lateral view. B, Ventral view. The arrows indicate new bone formation in the distracted region of the membranous bone onlay graft. Bone resorption is noted at the pin fixation region in A.
mandibular segment in all dogs. This was comprised of a proximal and distal sclerotic zone sandwiching a central radiolucent zone. There was no radiodense region in the distraction zone of the membranous bone onlay graft in dog 1. In dogs 2 and 3, there were small radiodense regions in the edge of the distraction zone of the membranous bone onlay graft. In dog 4, the full thickness of the distracted site in both the membranous bone onlay graft and the underlying mandibular segment showed zones of ossification proximally and distally, with a radiolucent central zone. By 6 weeks, the new bone became progressively radiodense and extended into the center of the distraction zone (Fig 6). HISTOLOGIC FINDINGS
The membranous bone onlay graft showed normal osteoblastic activity, and the bony architecture was similar to the underlying mandible (Fig 7). Under a magnification of 200, the number of viable vessels were 10 in the membranous bone onlay graft and 11 in the underlying mandible. These findings suggest that vascularization of the membraneous bone onlay graft returned to nearly normal. Extensive fibrosis and proliferation of many osteoblasts forming osteoid were seen in the central region of the distracted zone in the underlying mandible.
In a serial histologic study using dogs, Karp et al39 divided the bony regenerate into 4 zones of healing: 1) a fibrous central zone, 2) a transition zone of early bone formation, 3) a bone remodeling zone of early bone formation, and 4) a zone of mature bone. They suggested that the primary mechanism of bone formation in the mandible was predominantly by intramembranous ossification, with a gradient of mineralization from a central fibrous interzone. Califano et al4 described the histologic development of the bony regenerate in 3 phases: 1) a colloidal phase (after 2 weeks), 2) a fibrillar phase (after 5 weeks), and 3) a lamellar phase (after 8 weeks). These experimental results showed that distraction osteogenesis induced new bone formation in the maxillofacial complex by direct mesenchymal induction rather than by cartilage formation, as in the long bones. Kumuro et al8 reported that the new bone produced by distraction osteogenesis was formed by both intramembranous and endochondral ossification. Endochondral bone healing also has been reported in mandibular experimental models.4,6,7 However, most authors believe that cartilage formation is a sign of either low oxygen tension or micromovement of the regenerate caused by instability during osteodistraction. Recently, Mehrara et al22 Showed that transforming growth factor-1 production may be an important regulator of vasculogenesis and that osteocalcin gene expression coincides temporally with mineralization during rat mandibular distraction osteogenesis. Our microscopic observations confirmed that the greater portion of new bone in the distracted region of normal mandible and in the mem-
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FIGURE 6. Ventral radiographs at 6 weeks after distraction. A, Dog 1. The arrow indicates a radiolucent region at the edge of the distracted region between the membranous bone onlay graft. B, Dog 3. C, Dog 4. The new bone is radiodense.
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FIGURE 7. Histologic section of the membranous bone onlay graft. There are many active osteoblasts and blood vessels (arrows) in the lacunae (hematoxylin & eosin stain, original magnification ⫻200).
branous bone onlay graft was generated by intramembranous bone formation. Cartilage formation only filled a small portion of the distraction gap. The gain in length ranged from 6 to 8 mm, yet the device was activated 10 mm. These results can be explained by convergence of the distraction vector in the device used. To have exact activated length, use
DISTRACTION OSTEOGENESIS
of 4 pins or an intraoral device to transmit the activation length to the distraction region is recommended. Havlik and Bartlett14 and Klein and Howaldt15 confirmed that protection of the periosteum does not seem to be necessary in mandibular distraction in children. Because of its rich blood supply, the craniofacial skeleton, can tolerate a more liberal elevation of the periosteum and a complete osteotomy. Knize et al23 observed enhanced survival of nonvascularized bone grafts with retained periosteum. They suggested that the periosteum provides a surviving population of osteogenic cells and a route for earlier revascularization of the bone graft. Thompson and Casson24 postulated that the periosteum aided the process of circulatory reanastomosis. Ozerdem et al40 showed the possibility of distraction osteogenesis in periosteal bone grafts and provided information regarding the importance of the periosteum and its osteogenic capacity. We did not include periosteum with the membranous bone onlay graft. In dog 1 and dog 4, the membranous bone onlay graft showed partial resorption caused by inflammation. We believe that if the membranous bone onlay graft had retained its periosteum this would have prevented the resorption and enhanced earlier revascularization.
FIGURE 8. Histologic section of the mandible of dog 1 at 6 weeks after distraction. A, The distracted region in the underlying mandible is almost fully bridged by new bone, leaving a small fibrous interzone (hematoxylin & eosin stain, original magnification ⫻5). Arrows indicate the distraction gap. B, A small number of cartilage islands and immature woven bone are seen (hematoxylin & eosin stain, original magnification ⫻40).
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FIGURE 9. Histologic section of the membranous bone onlay graft and underlying mandible in dog 2 at 6 weeks after distraction. A, The distracted region of the membranous onlay bone graft is almost bridged by fibrous tissue. Osteogenesis (arrow) is seen at the edges of the distracted area (hematoxylin & eosin stain, original magnification ⫻5). B, Schematic diagram of histologic section. A, membranous bone onlay graft; B, normal mandibular body; C, osteogenesis at the edge of the distracted region; D, fibrous interzone; E, new bone formation by periosteal reaction on the medial surface. C, High power view showing abundant active osteoblasts forming woven bone at the edges of the distracted region of the membranous bone onlay graft (hematoxylin & eosin stain, original magnification ⫻40).
FIGURE 10. Histologic section of the membranous bone onlay graft in dog 4 at 6 weeks after distraction. The underlying mandible and its distracted region were removed. A, The distracted region of the membranous bone onlay graft (arrow) is almost filled with woven bone (hematoxylin & eosin stain, original magnification ⫻10). B, Schematic diagram of histologic section. A, membranous bone onlay graft; B, woven bone in the distracted region; C, narrow fibrous interzone. C, Magnification of the distracted region of the membranous bone onlay graft. Woven bone (A) and islands of cartilage (B) are seen (hematoxylin & eosin stain, original magnification ⫻100).
1032 Numerous factors act to influence bone graft survival. Early revascularization is thought to be the most important factor for a successful graft. Cutting and McCarthy,25 La Trenta et al,26 and Antonyshyn et al27 all showed that vascularized membranous bone grafts in the immature dog model retain the normal architecture, with minimal resorption and considerable subperiosteal callus formation, and that they continue to grow. Although it has been recognized that vascularized bone transfers are superior in the growing child, vascularized bone transfers are technically much more difficult to harvest and shape and also there are limited donor sites. In the majority of instances in craniofacial reconstruction in the growing child, nonvascularized membranous bone onlay grafts may be preferable. Rigid fixation techniques and high oxygen tension in the healing environment have been shown to aid in the primary repair of membranous bone.32 Phillips and Rahn35 emphasized that bone resorption predominated in the presence of movement in regions with intermittent contact or poor fixation. They noted that membranous bone showed greater revascularization at 2 weeks when fixed than when not fixed. The stability of the fixation during the entire distraction procedure may be important, not only in relation to the recovery of vascularity but also to the cellular response. Smith and Abramson,30 Zins and Whitaker,31 and Kuziak et al32 showed that nonvascularized membranous bone grafts undergo less resorption than endochondral bone grafts in animal models. They suggested that the increased volume of the membranous bone graft was most likely caused by either more rapid revascularization, and hence greater graft survival, or delayed revascularization and hence delayed bone graft resorption. Endochondral bone grafts are believed to be more susceptible to resorption because of the less dense structure of the trabeculae. Wilkes et al33 studied the survival of onlay bone grafts in mature and immature animals and found that membranous bone survived twice as well as endochondral bone. Ozaki and Buchman38 reported that cortical bone grafts maintain their volume significantly better than cancellous bone grafts, and they believed cortical bone to be a superior onlay grafting material, independent of its embryologic origin. In our study, we used the zygomatic arch as a donor site because it is easy to harvest and because it shortens the operation time. However, it is rare for the zygomatic arch to be used as a donor site of the membranous bone clinically. Calvarial bone is the ideal graft choice and can provide a readily available source for craniofacial reconstruction. We expected vascularization of the membranous bone graft from the neighboring tissues and new
DISTRACTION OSTEOGENESIS
bone formation between membranous bone onlay graft. Our results showed no new bone formation in dog 1, partial new bone formation at the edges of the distraction zone in dog 2 and 3, and nearly normal bone formation in dog 4. Soft tissue dissection for the osteotomy and the osteotomy itself probably affected the revascularization of the membranous bone onlay graft from the neighboring tissues. This delayed revascularization of the graft resulted in initial minimal osteoblastic activity after distraction. We believe that to have new bone formation in a membranous bone onlay graft, distraction should not be done until at least 4 weeks after bone grafting. Kocabalkan et al13 and Havlik and Bartlett14 reported repeated bilateral mandibular lengthening in a patient with a severely hypoplastic mandible. Roth et al20 did a quantitative volumetric assessment of the mandible after distraction osteogenesis using computed tomography scans and reported a mean increase of 27% in the distracted hemimandible and 25% in the bilaterally distracted mandibles. Even though the soft tissue and bony volume was increased after distraction, occasionally the increased volume was not enough to correct the severe hypoplasia of the facial bones. Polley et al19 believed that skeletal reconstruction in patients with severe craniofacial microsomia should be performed with a combination of distraction osteogenesis of the mandible and free vascularized scapula bone grafts. The bone graft was distracted along with the native mandibular ramus. Corcoran et al21 reported 8 patients with craniofacial microsomia who had undergone costochondral rib graft reconstruction of the ramus (average 5.1 years earlier) and then had been submitted successfully to distraction osteogenesis to lengthen the deficient mandible. They also showed that the previous osteotomy sites were also amenable to distraction and that previously distracted mandibles could undergo successful sagittal split osteotomies. It was generally postulated that it is safe to perform distraction of a membranous bone onlay graft 6 months or more after placement. There are no exact data regarding the earliest time for distraction of the membranous bone onlay graft in patients with severe hemifacial microsomia. Our results show that distraction osteogenesis in a membranous bone onlay graft is possible in dog model at 4 weeks. However, clinical evaluation is necessary.
References 1. McCarthy JG, Schreiber J, Karp N, et al: Lengthening the human mandible by gradual distraction. Plast Reconstr Surg 89:1, 1992 2. Karaharju-Suvanto T, Peltonen J, Kahri A, et al: Distraction osteogenesis of the mandible. An experimental study on sheep. Int J Oral Maxillofac Surg 21:118, 1992
CHO, SEO, AND BAIK 3. Block MS, Daire J, Stover J, et al: Changes in the inferior alveolar nerve following mandibular lengthening in the dog using distraction osteogenesis. J Oral Maxillofac Surg 51:652, 1993 4. Califano L, Cortese A, Zupi A, et al: Mandibular lengthening by external distraction: An experimental study in the rabbit. J Oral Maxillofac Surg 52:1179, 1994 5. Ganey TM, Klotch DW, Slater-Haase AS, et al: Evaluation of distraction osteogenesis by scanning electron microscopy. Otolaryngol Head Neck Surg 111:265, 1994 6. Guerrissi J, Ferrentino G, Margulies D, et al: Lengthening of the mandible by distraction osteogenesis: Experimental work in rabbits. J Craniofac Surg 5:313, 1994 7. Gantous A, Phillips JH, Catton P, et al: Distraction osteogenesis in the irradiated canine mandible. Plast Reconstr Surg 93:164, 1994 8. Kumuro Y, Takato T, Harii K, et al: The histologic analysis of distraction osteogenesis of the mandible in rabbits. Plast Reconstr Surg 94:152, 1994 9. Klotch DW, Ganey TM, Slater-Haase A, et al: Assessment of bone formation during osteoneogenesis: A canine model. Otolaryngol Head Neck Surg 112:291, 1995 10. Sawaki Y, Ohkubo H, Hibi H, et al: Mandibular lengthening by distraction osteogenesis using osseintegrated implants and an intraoral device: A preliminary report. J Oral Maxillofac Surg 54:594, 1996 11. Block MS, Chang A, Crawford C: Mandibular alveolar ridge augmentation in the dog using distraction osteogenesis. J Oral Maxillofac Surg 54:309, 1996 12. Habal MB: New bone formation by biological rhythmic distraction. J Craniofac Surg 5:344, 1994 13. Kocabalkan O, Leblebicioglu G, Erk Y, et al: Repeated mandibular lengthening in Treacher Collins syndrome: A case report. Int J Oral Maxillofac Surg 24:406, 1995 14. Havlik RJ, Bartlett SP: Mandibular distraction lengthening in the severely hypoplastic mandible: A problematic case with tongue aplasia. J Craniofac Surg 5:305, 1994 15. Klein C, Howaldt HP: Lengthening of the hypoplastic mandible by gradual distraction in childhood—a preliminary report. J Craniomaxillofac Surg 23:68, 1995 16. Pensler JM, Goldberg DP, Lindell B, et al: Skeletal distraction of the hypoplastic mandible. Ann Plast Surg 34:130, 1995 17. McCormick SU, McCarthy JG, Grayson BH, et al: Effect of mandibular distraction on the temporomandibular distraction on the temporomandibular joint: Part 1 canine study. J Craniofac Surg 6:358, 1995 18. Molina F, Ortiz-Monasterio F: Mandibular elongation and remodelling by distraction: A farewell to major osteotomies. Plast Reconstr Surg 96:825, 1995 19. Polley JW, Brecker GL, Ramasastry S, et al: Simultaneous distraction osteogenesis and microsurgical reconstruction for facial asymmetry. J Craniofac Surg 7:469, 1996 20. Roth DA, Gosain AK, McCarthy JG, et al: A CT scan technique for quantitative volumetric assessment of the mandible after distraction osteogenesis. Plast Reconstr Surg 99:1237, 1997 21. Corcoran J, Hubli EH, Salyer KE: Distraction osteogenesis of costochondral neomandibles: A clinical experience. Plast Reconstr Surg 100:311, 1997
1033 22. Mehrara BJ, Rowe NM, Steinbrech DS, et al: Rat mandibular distraction osteogenesis: II. Molecular analysis of transforming growth factor beta-1 and osteocalcin gene expression. Plast Reconstr Surg 103:536, 1999 23. Knize DM, Gerskberg H, Ballantyne DL: Hormonal enhancement of autologous onlay bone grafts. Surg Forum 24:511, 1973 24. Thompson N, Casson JA: Experimental onlay bone grafts to the jaws. A preliminary study in dogs. Plast Reconstr Surg 46:341, 1970 25. Cutting CB, McCarthy JG: Comparison of residual osseous mass between vascularized and nonvascularized onlay bone transfers. Plast Reconstr Surg 72:672, 1983 26. La Trenta GS, McCarthy JG, Cutting CB: The growth of vascularized onlay bone transfer. Ann Plast Surg 18:511, 1987 27. Antonyshyn O, Colcleugh RG, Anderson C: Growth potential in onlay bone grafts: A comparison of vascularized and free calvarial bone and suture bone grafts. Plast Reconstr Surg 79:12, 1987 28. Bartlett SP, Whitaker LA: Growth and survival of vascularized and nonvascularized membranous bone: An experimental study. Plast Reconstr Surg 84:783, 1989 29. Muschler GF, Lane JM: Orthopedic surgery, in Habal MB, Reddi AH (eds): Bone Grafts and Bone Substitutes. Philadelphia, PA, Saunders, 1992, pp 381-382 30. Smith JD, Abramson M: Membranous vs endochondral bone autografts. Arch Otolaryngol Head Neck Surg 99:203, 1974 31. Zins JE, Whitaker LA: Membranous versus endochondral bone: Implications for craniofacial reconstruction. Plast Reconstr Surg 72:778, 1983 32. Kuziak JF, Zins JE, Whitaker LA: The early revascularization of membranous bone graft. Plast Reconstr Surg 76:510, 1985 33. Wilkes GH, Kernahan DA, Christenson M: The long term survival of onlay bone grafts: A comparative study in mature and immature animals. Ann Plast Surg 14:374, 1985 34. Bassett CAL, Herrman I: Influence of oxygen concentration and mechanical factors on differentiation of connective tissue in vitro. Nature 190:460, 1961 35. Phillips JH, Rahn BA: Fixation effects on membranous and endochondral onlay bone graft resorption. Plast Reconstr Surg 82:872, 1988 36. Goldstein JA, Mase CA, Newman MH: The influence of bony architecture on fixed membranous bone graft survival. Ann Plast Surg 34:162, 1995 37. Phillips JH, Rahn BA: Fixation effects on membranous and endochondral onlay bone graft revascularization and bone deposition. Plast Reconstr Surg 85:891, 1990 38. Ozaki W, Buchman SR: Volume maintenance of onlay bone grafts in the craniofacial skeleton: Micro-architecture versus embryologic origin. Plast Reconstr Surg 102:291, 1998 39. Karp NS, McCarthy JG, Schreiber JS, et al: Membranous bone lengthening: A serial histologic study. Ann Plast Surg 29:2, 1992 40. Ozerdem OR, Kivanc O, Tuncer I, et al: Callotasis in nonvascularized periosteal bone grafts and the role of periosteum: A new contribution to the concept of distraction osteogenesis. Ann Plast Surg 41:148, 1998