A device for treating fractures of a bone, comprising: a frame; a plurality of arms, each arm including a second portion extending between a proximal end pivotally coupled to the frame and a distal end pivotally coupled to a proximal end of a first portion of the arm, the first and second portions of each of the arms being pivotal about axes perpendicular to longitudinal axes of the corresponding first and second portions; a coupling at a distal end of each of the first portions each coupling lockingly receiving a bone fixation element to be secured to a corresponding bone fragment such that each of the arms can be coupled to a corresponding fragment of the bone; a mechanical unit supplying motion to the arms to move each of the arms relative to the frame; and a controller receiving data corresponding to a desired final position of the bone 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, characterized in that the device further comprises a first wrist portion between the distal end of a first one of said first portions and a first one of the couplings, the first wrist portion permitting the first coupling to rotate relative to the distal end of the first portion of the first arm, wherein the first wrist portion includes a first plate attached to a proximal end of the first coupling and a first shaft expending through the first portion, the first shaft being pivotably attached to the first plate to permit the first coupling and the first plate to pivot thereabout. a frame; a plurality of arms, each arm including a second portion extending between a proximal end pivotally coupled to the frame and a distal end pivotally coupled to a proximal end of a first portion of the arm, the first and second portions of each of the arms being pivotal about axes perpendicular to longitudinal axes of the corresponding first and second portions; a coupling at a distal end of each of the first portions each coupling lockingly receiving a bone fixation element to be secured to a corresponding bone fragment such that each of the arms can be coupled to a corresponding fragment of the bone; a mechanical unit supplying motion to the arms to move each of the arms relative to the frame; and a controller receiving data corresponding to a desired final position of the bone 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, characterized in that the device further comprises a first wrist portion between the distal end of a first one of said first portions and a first one of the couplings, the first wrist portion permitting the first coupling to rotate relative to the distal end of the first portion of the first arm, wherein the first wrist portion includes a first plate attached to a proximal end of the first coupling and a first shaft expending through the first portion, the first shaft being pivotably attached to the first plate to permit the first coupling and the first plate to pivot thereabout.