Blood flow and mechanical properties of healing bone. Femoral osteotomies studied in rats.

In male Wistar rats, a transverse osteotomy at the midshaft of the femur was made, and the acute effects on bone flow were measured before and after reaming. Flow and mechanical variables in the healing bones were measured at 4, 8, and 12 weeks following osteotomy. Osteotomy reduced total bone blood flow by about 50 percent, and cortical flow in the diaphysis by approximately 40 percent. Cortical flow was equally diminished in the mid-diaphysis and in the osteotomy area, and no differences between the proximal and distal diaphyseal flows were found. Reaming of the osteotomized bones did not lead to any further flow reduction. At 4 weeks, total bone flow was more than doubled; increases were found in every segment of the fractured bone, and a more than 10-fold increase in the callus area was seen. At the end of the experiment, the femurs had regained 83 percent of their normal strength, 88 percent of normal rigidity and 78 percent of normal fracture energy. At this time total bone flow was marginally increased, flows in the proximal and the distal diaphyses were almost normalized, while a nearly 3-fold increase was still found in the callus area. Flow in the callus area gradually decreased during healing, and regression analysis demonstrated a negative correlation between callus flow and mechanical properties.