[Histologic finding of fracture healing using external fixation and its clinical significance]

The histology of bone healing under external fixation of fractures is studied in 2 human bone specimen and in the sheep's tibia. Primary bone healing occurs under absolute stable fixation. The regular course shows secundary bone healing by endosteal and periosteal callus formation, caused by motion in the fracture gap. Nonunion results, if motion is not big enough to induce callus formation and if motion is too big to allow primary bone healing. So one of the main problems in external fixation of fractures is to find out the adequate dose of stability and motion in the fracture gap. External fixation does not disturb the vascular supply of bone. Intramedullary vessels, that are cut during the osteotomy of the sheep's tibia, are perfectly regenerated 4-5 weeks later. In the surroundings of the Schanz' screws, cortical remodelling is the biomechanical response of bone to strees, which is generated by external fixation. This cortical remodelling can reduce compression, originally applied to the bone. The indication and the timing for a change to internal fixation is discussed.