A device for treating fractures of a bone comprises a plurality of arms, each extending from a proximal end to a distal end and movable in a three-dimensional space, the proximal end of each arm coupled to a frame and a plurality of couplings, each of the couplings coupled to a distal end of each of the plurality of arms, the coupling lockingly receiving a bone fixation element secured to a corresponding bone fragment such that each of the arms is coupled to a corresponding fragment of the bone in combination with a mechanical unit moving each of the arms relative to the frame and a controller receiving data corresponding to a desired final position of the fragments relative to one another and controlling the mechanical unit to move the arms relative to one another to achieve the desired final position of the bone fragments relative to one another.