We have experienced 40 cases of the tibial shaft fractures treated with Küntscher nail from 1979 to 1986. Authors analysed these cases and our own experimental study concerned with the shape of Küntscher nail. The shape of Küntscher nail for the tibial shaft fractures should be designed according to the type and location of the fracture. The proximally bent and distally straight nail is used for the extension fracture, proximally and distally bent nail or entirely bent nail is inserted for the flexion fracture of the tibia. The large nail(over 13 mm in diameter) may produce injury to the patella because it has minimal flexibility. In order to permit easy driven down of nail and prevent this injury, the nail should b. bent into three to four segments and the length of the longest segment should not exceed the permissible length of straight nail (Permissible length is distance from entrance of nail to posterior cortex of the upper fragment, where tip of the (nail impinged-about 12cm) The midpoint of the middle segment of dual dent nail is placed at the fracture site. The middle segment of the nail may bent anteriorly for flexion fracture and posteriorly for extension fracture, securing the dynamic fixation of the fracture.