Cortical revascularization after reamed and unreamed intramedullary nailing in the rabbit femur: a microangiographic histometric analysis.

BACKGROUND: Intramedullary nailing leads to a reduction in cortical bone blood flow. The relative effect of reamed versus unreamed nailing on the degree of avascularity and on revascularization of the cortex remains controversial. We compared the effects of reamed versus unreamed intramedullary nailing on cortical revascularization and the time course for its recovery in the unfractured rabbit femur. METHODS: A total of 56 New Zealand white rabbits were used as experimental animals. Reamed nailings with Kirschner wire (diameter, 3 mm) were performed in the right femora (group R, n = 49), and unreamed nailings with Kirschner wire (diameter, 2 mm) were performed in the left femora (group UR, n = 49) of the same animals after a standard surgical procedure. Microangiography that used Indian ink was performed for each killed animal at one of seven postoperative time periods: 2 hours, 3 days, and 1, 2, 3, 4, and 5 weeks after surgery. The right femora and the left femora of seven rabbits were used as the postoperative day 0 controls of group R and those of group UR, respectively. We evaluated the vascularization ratio (VR) in cross-sections according to the following formula: VR = the number of enhanced vessels with Indian ink/total cortical vessels. Each cross-section was divided into an inner and outer half, which were in turn divided into quarters, so that the entire cross-sectional are is represented by eight regions. The VR was calculated for each regions and then comparison was made between group R and group UR at various time periods and areas. RESULTS: No statistically significant differences were observed in VR at any time period between group R and group UR in total cortical area and total periosteal side. However, on the total medullary side, the VR of group UR was significantly higher than that of group R at postoperative day 3 (p = 0.04). Statistically significant differences were observed between the VR on the periosteal side and that on the medullary side in both groups at all time periods aside from the 5-week period (p < 0.05). Revascularization of the cortex occurred 4 weeks after intramedullary nailing in both group R and group UR. CONCLUSION: The periosteal circulation was maintained better than the medullary circulation, irrespective of whether the canal was reamed or not. The present study failed to detect any statistically significant differences in cortical revascularization between reamed nailing and unreamed nailing. Thus, we concluded that reamed and unreamed nailing are not differentially advantageous in the unfractured rabbit femur, in terms of impairment of cortical blood supply.