A surgical tool system for osteosynthesis of a fractured bone comprising bone fragments (20, 20', 20"), the surgical tool system comprising a registration instrument (10, 10') for registering a fractured bone fragment in a predefined position, the registration instrument comprising: - a first and a second contact surface (11, 12), wherein the first and the second contact surface (11, 12) meet at along an edge, wherein the first contact surface is an inverse surface of a first surface portion of a fragment of the fractured bone and the second contact surface is an inverse surface of a second surface portion of the fragment; - at least one guiding channel configured to provide guidance to a surgical tool for drilling pilot holes at predefined orientations and positions into a bone fragment; wherein the surgical tool system further comprises an osteosynthesis plate for rigidly fixing the fragments (20, 20', 20") together in a predefined position that corresponds to a position in which the bone should be reconstructed from the fragments, the osteosynthesis plate comprising a plurality of openings for receiving surgical tools, wherein the openings are designed to correspond to the positions and orientations of the pilot holes in the fragments (20, 20', 20") when the fragments (20, 20', 20") are repositioned in the predefined position; characterized in that the surgical tool system further comprises a post-registration instrument configured to align the fragments (20, 20', 20") of the fractured bone with the osteosynthesis plate, while the osteosynthesis plate is arranged at the fragments (20, 20', 20"), wherein the post-registration instrument is configured to align the positions of the pilot holes with the centers of the openings of the osteosynthesis plate; wherein the post-registration instrument comprises centering channels for receiving surgical pins attached to different fragments (20, 20', 20") of the fractured bone, wherein the centering channels are configured to center the surgical pins with respect to the openings of the osteosynthesis plate. - a first and a second contact surface (11, 12), wherein the first and the second contact surface (11, 12) meet at along an edge, wherein the first contact surface is an inverse surface of a first surface portion of a fragment of the fractured bone and the second contact surface is an inverse surface of a second surface portion of the fragment; - at least one guiding channel configured to provide guidance to a surgical tool for drilling pilot holes at predefined orientations and positions into a bone fragment; the surgical tool system further comprises an osteosynthesis plate for rigidly fixing the fragments (20, 20', 20") together in a predefined position that corresponds to a position in which the bone should be reconstructed from the fragments, the osteosynthesis plate comprising a plurality of openings for receiving surgical tools, wherein the openings are designed to correspond to the positions and orientations of the pilot holes in the fragments (20, 20', 20") when the fragments (20, 20', 20") are repositioned in the predefined position; characterized in that the surgical tool system further comprises a post-registration instrument configured to align the fragments (20, 20', 20") of the fractured bone with the osteosynthesis plate, while the osteosynthesis plate is arranged at the fragments (20, 20', 20"), wherein the post-registration instrument is configured to align the positions of the pilot holes with the centers of the openings of the osteosynthesis plate; wherein the post-registration instrument comprises centering channels for receiving surgical pins attached to different fragments (20, 20', 20") of the fractured bone, wherein the centering channels are configured to center the surgical pins with respect to the openings of the osteosynthesis plate.