Osteotomy, a surgical operation that cut of the bone to correct the deformity, is standardised with the rules. They are especially developed after the distraction osteogenesis and Ilizarov`s principles. It is important to understand what ACA, CORA and angle midway are, to recognize them and to know how the changes will have consequences, in the planning of the intended treatment. Althougth that internal fixation became more popular in the past few years because of the higher patient comfort, it is now much more important to know the basics of external fixators which save the limbs especially in the salvage procedures, such as hinges, motor unit and gradual correction.