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 bl ood flow, The relative effect of reamed versus unreamed nailing on the degr ee of avascularity and on revascularization of the cortex remains controver sial, We compared the effects of reamed versus unreamed intramedullary nail ing on cortical revascularization and the time course for its recovery in t he 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 performe d in the right femora (group R, n = 49), and unreamed nailings with Kirschn er wire (diameter, 2 mm) were performed in the left femora (group UR, n = 4 9) of the same animals after a standard surgical procedure. Microangiograph y 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 a fter surgery. The right femora and the left femora of seven rabbits were us ed as the postoperative day 0 controls of group R and those of group UR, re spectively. We evaluated the vascularization ratio (VR) in cross-sections a ccording 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 cal culated for each regions and then comparison was made between group R and g roup UR at various time periods and areas, Results: No statistically significant differences were observed in VR at an y 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 t ime periods aside from the 5-week period (p < 0.05), Revascularization of t he cortex occurred 4 weeks after intramedullary nailing in both group R and group UR, Conclusion: The periosteal circulation was maintained better than the medul lary 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. Th us, we concluded that reamed and unreamed nailing are not differentially ad vantageous in the unfractured rabbit femur, in terms of impairment of corti cal blood supply.