The lengthening of long bones in children using the traction osteogenesis (desmogenesis) method is performed by the gradual stretching of the callus of the healing bone tissue, i.e. by the gradual lengthening 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 (after the completion of elongation). Changes in stresses and deformations initiated by external force and moment effects very efficiently regulate the velocity of healing, the formation of bearing structures in the tissue and, last, but not least, the development of adequate elastic and viscoelastic properties in the tissue.