Abstract: A device including a nail for gradually lengthening long bones including outer and inner sliding tubes connected by a double ratchet mechanism, the nail being fixed by its two extremities in the bone, and the device being entirely included in the concerned bone, being lengthened post-operatively by maneuvers applied on the limb. Rotation of a distal part of the limb with respect to proximal part of the limb allows rotation of the ratchet mechanism with lengthening of the device in one direction, and keeping of the gained length in the other direction while returning to the neutral axis of the rotation of the device, thereby featuring a dynamization system, and a system, to limit the range of rotation of the device.