Effect Of Lengthening Rate On Angiogenesis During Distraction Osteogenesis

Distraction osteogenesis generates new bone by utilizing a mechanism for wound healing,which is a new technology. In the bone sture or two sides of broken bone, it utilizes distraction system to distraction by invariably rate. Distraction osteogenesis generates new bone in bone gap to make bone lengthened and widened. It is a kind of endogenic tissue engineering which makes new bone form continuously by distraction to bone cross-section. The new bone moulds in the direction of the distraction .At the same time,the tissues of skin, aponeurosis, nerve, muscle, vessel and cartilage are adaptable rebuilded by the tension of surrounding soft tissue .The slow change can not only avoid the damage to soft tissue, but also ensure the positional stabilization of the new bone. Many studies suggested that the new bone formation was usually accompanied by angiogenesis. New bone formation had closed relation with angiogenesis . So it is very important that we study the effect of lengthening rate on angiogenesis during distraction osteogenesis.Objective: This study aims at investigating the effect of four varying rates(0.3, 0.7, 1.3and 2.7mm/day)of distraction on the vascularization process in rabbit modal of leg-lengthened during distraction osteogenesis.Methods: The experiment used New Zealand White rabbits , The rabbits were randomly divided into four groups, and performed a mid-femur osteotomy model. Each group was lengthened at the rate of 0.3, 0.7, 1.3 and 2.7mm/day, until the femur was lengthened 2.0 cm than original length . As soon as the appropriate length had been achieved , the regenerating tissues of the distraction gaps were collected. Immunostaining was performed with use of specific antibodies to endothelial cellantigen(CD34) . With using of the Chalkley counting method , staining blood vessel cells were examined semiquantitatively in the developing tissues. The result was analyzed by t test and mean square.Result:The number of positive-staining cells is statistically higher in the central fibrous zone of the 0.7and 1.3mm/day groups compared with any other zone of any group P<0.05.There are no statistical differences in the number of positive-staining blood vessel cells in the primary mineralization front and the new bone zone adjacent to the primary mineralization front P>0.05. The number of positive-staining cells in the new bone zone distant to the primary mineralization front is significantly decrease compared with elsewhere in the regenerated area in any group P<0.05 .Conclusion: The study indicates that the angiogenic process was affected by the rate of distraction. A slow rate of distraction (0.3mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vasculariation process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3mm/day.