RESTORATION OF BONE FLOW FOLLOWING FRACTURE AND REAMING IN RAT FEMORA

In rats, bilateral closed femoral fracture was produced after intramedullary 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 effects of fracture only. Following fracture, total bone blood flow was reduced to about 50 percent and cortical flow to about 40 percent of that 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 to approximately one third of normal flow. Cortical flow decreased to about one third and one quarter in the 2 groups. On Day 1, total flow was 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 bone blood flow and approximately a fivefold increase in cortical flow were found. On Day 9, a separate callus area was defined and flow measurement revealed a rich vascularized callus in both groups, but no differences between the groups were found. Following fracture, neither moderate 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 restoration of cortical bone blood flow. After 9 days, rich vascularized callus areas were found irrespective of the initial degree of reaming.