The aim of this study was to establish an objective evaluation method for intraoperative detection of damaged vascular endothelium in avulsion injuries. Twenty male Fischer rats were randomly assigned to control or experimental groups (n = 10, each). Crush-avulsion injury was performed on right femoral arteries. Resection of damaged segments was performed according to operative microscopic findings in the control group; fluorescein sodium was applied to the artery lumen before resection in the experimental group to help visualize the damaged endothelium. Microvascular repair was performed in five rats in each group. In the other animals, the whole length of the femoral arteries was resected to assess the actual extent of injury histologically. At the end of the follow-up period, patency of microvascular anastomoses was examined and the lengths of the resected segments were compared with the actual length of the injured segment measured histologically. The difference between these two measurements was statistically significant in the control group (p < 0.05) but not in the experimental group (p > 0.05). Anastomosis patency was significantly higher in the experimental group (p < 0.0001). In conclusion, fluorescein sodium may help to accurately determine the length of the injured vascular segment in avulsion injuries.