The lengthening of long bones in children using the traction osteogenesis method is performed by the gradual distraction of the opposite ends of bone fragments. Mechanical factors are of major importance for the development of the callus between two successive elongations, as well as during the time of its consolidation and modelling. New designed external fixator accelerates the healing process and stimulates the formation of callus and subsequent ossification. The limitation of pain during the actual lengthening process such as by selecting the appropriate size and frequency of distraction steps together with dynamic effect is also equally important.