New insights into the biology of fracture healing.

Distraction and segment transport are wellaccepted treatment modalities for fracture management.1-27 Intermittent distraction creates an axial mechanical strain in the soft-tissue envelope and mesenchymal tissue, replacing the fracture hematoma. This study reports the origin and different rates of new bone formation induced in bone defects by distraction and segment transport. MATERIALS AND METHODS This study was performed at the AO/ASIF Research Institute in Davos Platz, Switzerland, and was approved by the Ethics Committee of the Kanton Graubunden. Twenty adult female Swiss mountain sheep (average weight 62 kg) were included in this study, and were divided into two groups (A and B) of 10 animals each. They were operated under endotracheal anesthesia and strict sterile operating conditions. A modified four ringhybrid external fixation frame with calibrated vertical rods (8 15 cm) was mounted on the left tibial diaphysis (Figure 1). Each ring was mounted to bone by two 1.6-mm Kirschner wires (Synthes AG