RESTORATION OF BONE FLOW FOLLOWING FRACTURE AND REAMING IN RAT FEMORA

In rats, bilateral closed femoral fracture was produced after intramed ullary reaming to 1.6 mm on the left side and 2.0 mm on the right side . The fractures were fixed with 1.6 and 2.0 mm steel pins. Radioactive microspheres were used to determine bone blood flow at 30 min, 1 day, 3 days and 9 days after fracture. 8 rats were used to estimate normal bone blood flow, and an additional 8 rats to examine the vascular eff ects of fracture only. Following fracture, total bone blood flow was r educed to about 50 percent and cortical flow to about 40 percent of th at in intact bones. Fracture and reaming to 1.6 mm reduced total bone flow to 40 percent and reaming to 2.0 mm reduced the total bone flow t o approximately one third of normal flow. Cortical flow decreased to a bout one third and one quarter in the 2 groups. On Day 1, total flow w as practically normalized in both groups. Cortical flow in the 1.6 mm group was about equal to that of intact bones, while it was about one third of normal flow in the 2.0-mm group, and significantly less than the 1.6-mm group. On Day 3, total bone flow was more than double that of intact bones and cortical flow 3 times greater in both groups. Flow continued to increase to Day 9 when a threefold increase in total bon e blood flow and approximately a fivefold increase in cortical flow we re found. On Day 9, a separate callus area was defined and flow measur ement revealed a rich vascularized callus in both groups, but no diffe rences between the groups were found. Following fracture, neither mode rate nor aggressive intramedullary reaming seem to create any further impairment in bone flow. Following fracture and reaming, blood flow is rapidly restored, however, extensive reaming results in a delayed res toration of cortical bone blood flow. After 9 days, rich vascularized callus areas were found irrespective of the initial degree of reaming.