Distraction osteogenesis is now a standard method for bone lengthening. However, little is known about the exact mechanism of new bone formation. This study was undertaken to investigate the temporal and spatial changes of angiogenesis during the periods of distraction osteogenesis; the three-dimensional microarchitecture of newly formed vessels and their origin; and the role of angiogenesis with reference to mineralization.

Sprague-Dawley rat's tibia was osteotomized subperiosteally and was distracted at a rate of 0.5 mm per day for two weeks after one week of latency period. Vascular corrosion casting using Mercox was done on the hindlimbs before osteotomy, and at the 1st, 2nd, 3rd, 4th, and 6th weeks postoperatively. Replicated microvascular structures and their distribution patterns at the distraction site and adjacent parent bone were observed temporally and spatially under scanning electron microscope. These findings were compared with radiographical and histological observations.

1. At postoperative first week and second week, proliferation of periosteal vessels were more pronounced than that of endosteal vessels, which corresponded to the early new bone formation in subperiosteal area on histologic sections. 2. At postoperative third week, arterial branches from the medulla of parent bone entered into the distraction gap. Multiple longitudinal vascular branches sprouted out from the newly formed vascular network, and ran towards the interzone. 3. At postoperative fourth week, there was vascular proliferation in the periosteal side of interzone, from which branches arose towards the parent bone. 4. At postoperative sixth week, vascular networks of both sides connected to each other, and few angiogenetic findings were observed.

In distraction osteogenesis, angiogenesis occurred actively during the distraction period and then gradually decreased with time. Taken together with radiographical and histological findings, close temporal and spatial relationship between the angiogenesis and new bone formation at the distraction site was revealed.