External callus formation of closed femoral shaft fractures treated by medullary fixation.

Various radiographic patterns were observed for external callus formation of closed femoral shaft fractures treated by closed and open medullary Rush pin fixation. Closed pinning tends to form more adequate lateral callus, to have less looping of bridging callus over the cortex, and to form smooth, dense callus. Open pinning tends to form less lateral callus, to have more looping (radiolucent space under callus) of the callus over the cortex and fracture site, and to have areas of exuberant callus with the appearance of myositis ossificans. The circulatory status of the cortex and soft tissues seem to be a factor in these callus patterns. Avascular cortex of shaft fractures is inferred by the radiographic findings of bridging callus loops over the cortex, relative increased density of cortical bone, and resorption of cortical bone.