Experimental Study On Anginogenesis Of Nonvascular Transport Distraction Osteogenesis

Objective:To investigate the anginogenesis, the expression of vascular endothelial growth factor (VEGF) and reconstruction of blood supply of nonvascular transport distraction osteogenesis in dog mandibles,and to further study its possible bio-mechanisms of osteogenesis.Methods:9 healthy adult dogs were chosen.8 of them were randomly divided into four groups with two of each group according to different consolidation periods of 2,4,8 and 14weeks and conducted osteotomies in the inferior half of right mandibular bodies to form a 10.0-mm in length by 10.0-mm in height segmental skeletal defects. Then a 15.0-mm in length by 10.0-mm in height marginal partial 10.0-mm free nonvascular bony transport discs were prepared at the mesial stumps of mandibles and custom-made internal distracters were installed in place as designed. After 5-day latency period distracters were initiated and activated at lmm/d. All animals were sacrificed after different consolidation periods. The regenerated bone specimens harvested from distracted mandibles were assessed with macromorphological, hematoxylin-eosin stained histological, VEGF immunohistochemical examination, respectively.-1 adult dog was conducted with the same surgery, sacrificed at 4 week and assessed with ink perfusion examination.Results:1.Specimens macrography All animals finished distraction process without severe complications. The distraction region and transport disc were surrounded by sleeve-like soft tissue. A great amount of new bones formed around transport disc and in disctracton region. The mandible defect was well repaired. Superior bones regenerated surrounding in lingual sides and inferior ones in buccal sides were observed.2. Histological examination Histology showed that at 2 week there was granulation tissue in distraction region, a large number of fibroblasts and collagen fibers, capillary proliferation were observerd; In transport disc, the edge of buccal cortical bone was continuous while osteoclasts could be observed on the edge of lingual side which was erosion like obsrobed; At 4 week numerous new capillaries formed among the new trabecular bones in distraction region; On both buccal and ligual side of transport disc, disordered new trabeculae bones formed under the periosteal. Blood vessels increased. The new bones of lingual side was surperior to buccal side ones; At 8 week in distraction region mature trabecular bones were observed, haversan canals formed and the number of blood vessels was less than 4 week; In transport disc, most of the orignial bones were replaced by new bones and the matrix was increased, while blood vessels were maturer; At 14 weeks in distraction region, calcified bone remoded, blood vessels were similar to the normal bone tissue. Nearly all of the transport disc was replaced by new bones. Blood vessels were less than 8 week. The structure of transport disc was similar to normal bone.3. Immunohistocheistry In non-vascularized transport distraction osteogenesis model, at 2 weeks in distraction region, diffuse and strong expression of VEGF could be observed in granulation tissue, while a small amount of bone tissue on the edge of transport disc showed low expression of VEGF; At 4 week, lots of new blood vessels in periosteal and among new trabeculae bones strongly expressed VEGF, while high VEGF expression could be observed-on the eage of and within the transport disc and the original bone tissue of transport disc negatively expressed VEGF; At 8 week, VEGF expression could be observed on the inner side of periosteum which was beside the trabecular bones. Blood vessels on the edge and internal of transport disc expressed VEGF; At 14 weeks in distraction region, only periosteal and a few of new bones weakly expressed VEGF. A few of blood vessels with low' VEGF expression were on the edge and internal of transport disc. The result of gray value test illustrated that a substantial increase in the expression of the VEGF was found in both distraction region and rionvascular transport disc compared to the controls(p<0.05). At the time of 2 and 4 week of consolidation, the expression of VEGF in distraction region showed higher than that in transport disc(p<0.05), Whereas at 8 week and 14 week, the staining intensity of VEGF in both region was similar(p>0.05). At the time of 2 and 4 week of consolidation, the expression of VEGF in distraction region and transport disc respectively reached their peak, with the time of consolidation elapsing, the expression of VEGF gradually decreased.4. Ink perfusion At 4 week, on the edge of transport disc blood vessels from the surrounding soft tissues and periosteum grew into the cortical bone. On lingual side blood vessels formed more richly than buccal side in transport disc.Conclusions:In nonvascular transport distraction osteogenesis, the mode of revascularization was as traditional distraction osteogenesis one though with certain characteristics of free bone grafting simultaneously. At the early stage, the transport disc exerted the similar function as traditional vascular transport disc. A great amount of new bones formed around transport disc and in disctracton region. These sleeve-like new bones provided blood supply for transport disc to complete its creeping substitution, as well as exerted the function as a mechanical and biological barrier to protect the transport disc and avoid its infection. Due to its better blood supply, superior bones regenerated in lingual sides and inferior ones in buccal sides. Lingual area of transport disc may be the germinal center, where new bone and new blood vessels primarily formed, gradually grew into and replaced the transport disc. VEGF plays an important role in the angiogenesis and bone healing in nonvascular transport distraction osteogenesis. The angiogenesis and bone formation of nonvascular transport distraction osteogenesis were the comprehensive results of interactions of many factors such as distraction, friction and micro trauma.