It is not easy to insert a locking screw into the transverse holes for fixing the broken human bone by the intramedullary nail. Generally, the X-ray image was used in conjunction with a target device to detect the hole position. But the X-ray exposure has very crucial problem for doctors and patients. In order to overcome this problem, an ultrasound was utilized for determining the hole position. However, the practically useful method was not yet investigated sufficiently.

In this paper, the central position of the transverse holes in intramedullary nail inserted into the pig femur was detected using the ultrasonic pulse echo method by immersion technique. After that, the locking screw was penetrated toward the transverse holes. Then, the cross section of the specimen was observed using the X-ray image and the interlocking accuracy of locking screw was investigated. As this result, it was found that the proposed ultrasonic method was able to determine precisely the central position of the transverse holes in intramedullay nail.