Although the seriously radiation injury to both patients and surgeons through the detection of the hole under osteosynthesis using interlocking nailing has been noted in some papers, the clinical results generally have been good. We have developed a new designed intramedullary rod with a small slot and the effectively ultrasonic detection technique for an interlocking hole while the improved detection procedure to relieve this injury is described as technically difficult. The goal of this paper is to present the optimal design of intramedullary nailing using FEM analysis and to describe the effect of the factors that are likely to result in success or failure.