Effect of lengthening rate on angiogenesis during distraction osteogenesis

This study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg-lengthen ing. Immunostaining was performed with use of specific antibodies to type-I V collagen and endothelial cell antigen to examine semiquantitatively the p resence of blood vessels in the developing tissues. With use of the Chalkle y counting method, the greatest number of positive-staining blood vessel ce lls was found in the central fibrous zone of the groups that underwent leng thening at 0.7 and 1.3 mm/day compared with any other zone in any group(p < 0.05, t test). There were no statistical differences in the positive label ing indices in the mineralization front and the new bane zone adjacent to t he mineralization front in any of the groups. However, the decrease in the number of positive-staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction oste ogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary netw ork at the junction of the mineralization front and the fibrous zone. The a ngiogenic response was weaker in the more mature regions within the new bon e zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulat e angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesi s,the vascularization process in the central fibrous zone was maximally sti mulated at distraction rates of 0.7 and 1.3 mm/day.