In vitro analysis of distraction osteogenesis

Distraction osteogenesis has been widely used for lengthening craniomaxillofacial bone. The healing process of distracted bone has been studied mainly by histological observation in vivo. To analyze the cellular response to the mechanical stress of distraction, we have established and evaluated an in vitro model of distraction osteogenesis using an organ culture technique. Five-week-old male Wistar rats were used for the experiments. The tibial bone was fractured by hand and fixed for 1 week by acrylic resin. After the initial healing period, the tibial bone was harvested and used for this study. A distraction instrument was devised to control the strain on the cultured bone using a micrometer. After distraction, the samples were histologically evaluated for ossification by hematoxylin and eosin stain and Alcian blue stain. As a result, the histological finding for the bone region at a slow rate of distraction (0.5 mm/day) was different from that at a rapid rate of distraction (1.0 mm/day). The proliferation of cartilage was inhibited at the rapid distraction rate. Thus, we hypothesized that mechanical stress regulated cartilaginous growth in tissue cultivation. Judging from this experiment, the model was useful for investigation of the mechanism of bone formation in distraction osteogenesis, because it was simple and served to isolate many factors.