PURPOSE : We have studied medullary canal widening effect on anteroposterior plane by intramedullary nails with distal anterior bend in the surgical treatment of tibial fracture and signified the clinical importance of the effect. MATERIALS AND METHODS : Ineramedullary tibial nails with distal anterior bend, Russell-Taylor(R)and AIMTMtibial nails were compared and the amount of medullary canal widening was calculated mathematically using the length and angle of distal anterior bend of the nails. the length and angle of distal anterior bend of Russell-Taylor(R)and AIMTMtibial nails were 64mm, 3 and 47.5mm, 5 , respectively. RESULTS : The amount of medullary canal widening on anteroposterior plane by Russell-Taylor(R)and AIMTM tibial nails were 2.81mm and 3.26 mm more than the nail diameter, respectively. CONCLUSION : On insertion of tibial nails with distal anterior bend, the medullary canal widening effect on anteroposterior plane by the nails should be carefully considered. We think it will be better to insert these nails with unreamed technique or to insery smaller diameter nails after minor reaming and forceful blow should be avoided especially when the nail passes down through the isthmic portion of the tibial diaphysis to prevent the fracture of isthmic portion.