Abstract
The viability and osteogenic potential of bone cylinders for bone transport was investigated in one tibia of 18 mature male New Zealand rabbits. The length of the bone cylinder was equal to or twice that of the diameter of the tibia. The cylinder was cut subperiosteally with an externally cooled oscillating saw from a lateral approach, after a specific unilateral external fixator had been applied. To simulate bone transport, one end of the cylinder was fixed to the distal bone stump by a cerclage wire and healing and revascularization was prevented by an interposed expanded polytetrafluoroethylene membrane. The periosteum was readapted and sutured, and distraction began 10 days postoperatively at 0.25 mm/12 hours for 22 days. New bone formation in the distraction gap was quantified by dual energy xโray absorptiometry and by computerโassisted histomorphometry of polyfluorochromeโlabeled undecalcified bone sections and corresponding microradiographs. In half of the animals with each size cylinder, osseous bridging occurred, so the findings on distraction osteogenesis are reported only for the remaining nine animals. Generally, centripetal mineralization of the gap with two distinct zones of ripening bone structures and a central radiolucent fibrocartilaginous zone could be distinguished. Neither absorptiometry nor histomorphometry showed significant differences in the overall amount of this new bone formation for the bone cylinders of two different lengths. However, osteogenesis was significantly greater at the proximal end than at the cylinder. New bone was formed predominantly from endosteal sites in the smaller cylinders and from periosteal sites in the larger cylinders. Histologically, there was complete necrosis of both sizes of cylinders, followed by revitalization through newly formed vascular channels. This process started earlier and was more pronounced with the smaller bone cylinders. It is concluded from these experiments that even careful subperiosteal osteotomy with an oscillating saw leads to necrosis of both small and large bone cylinders. However, distraction osteogenesis still can be achieved and is mediated mainly by the revitalized endosteum in the smaller cylinders and by the periosteum, which apparently can be better preserved, in the larger cylinders. These results demonstrate the feasibility of even extremely small bone cylinders for distraction osteogenesis; the minimum length is determined only by the possibility of stable fixation.