Objectives

The monitoring of fracture healing is a complex process. Typically, successive radiographs are performed and an emerging calcification of the fracture area is evaluated. The aim of this study was to investigate whether different bone healing patterns can be distinguished using a telemetric instrumented femoral internal plate fixator.

Introduction: The rotational fiexibility of the occipito-atlanto-axial complex is infiuenced by several ligaments, capsules and the alarian ligament (AL). For the development of a biomechanical model simulating dens fractures and stabilization techniques, we investigate the rotational range of motion of the atlantodental joint reducing sequentially the infiuence of capsules and additional ligaments in two different groups (segments C0–C2 and segments C1–C2). The torque affecting the dens axis was analyzed.

Methods: 7 fresh C0–C2 + 7 fresh C1–C2 cadaver segments with the integrity of all ligaments and joint capsules were mounted on a custom made rotational testing device (RTD) of a universal mechanical testing machine (UTM). Pure axial torque with a rotational speed of 5°/s was applied clockwise and counter-clockwise. To acquire the physiological range of motion (ROM) between C1 and C2, a maximal axial torque of ±1.5Nm was applied. Consecutively, all the ligaments which do not attach to the odontoid were transected and the ligaments which attach to or contact with the odontoid were preserved. The previously recorded rotation was applied to the specimens with the RTD. The torque between C1 and C2 was recorded.

Results: The group C0–C2 had a mean unidirectional ROM of 23.45° at 0.3Nm and of 32.87° at 1.5Nm respectively. The group C1–C2 had a larger ROM of 27.41° at 0.3Nm and of 35.47° at 1.5Nm. After resection of ligaments the torque in Group C0–C2 was reduced by 38% (0.3 Nm) and 61% (1.5Nm) respectively. The group C1–C2 showed a higher reduction of the transmitted torque: 90% (0.3Nm) and 80% (1.5Nm) respectively.

Discussion: Evaluating the direct torque forces on the atlantodental joint, we sequentially cut the ligamentous junction of the C1–C2 complex. ROM measurements at 0.3 Nm correlate well to previous data. Measurements in the group with cut AL (C1–C2) had an increased ROM. Comparing the reduction of the transmitted torque between the two groups, 90% (0.3Nm) and 80% (1.5Nm) in group C1–C2 in contrast to only 38% (0.3Nm) and 61% (1.5Nm) in group C0–C2, the rotationally stabilizing meaning of the AL in the occipito-atlantodental complex is punctuated. Higher torques (1.5Nm) increased the reduction of the transmitted torque in group C0–C2 between the measurements with intact and with cut ligaments. We hypothesize that the torque acting on the atlantodental joint is dominated by the AL at smaller angles and has to be considered in the evaluation of upper cervical models. In higher angles the torque is predominately determined by the capsules. Transferring the data to a model simulating the torque on the dens, a clear distinction has to be made based upon the region of the ROM. For larger angles at the borders of the ROM, the infiuence of the facet joint capsules cannot be neglected.

Fully automated robots for the planning and implantation of total hip arthroplasty have completely withdrawn from the market. Reasons were technical problems during the reaming process that lead to postoperative neurological problems. This lead, especially in Germany, to numerous court cases and created a hostile environment regarding robotic orthopaedic surgery.

The first steps in the development of a robotic assisted system for total hip arthroplasty are presented. This system will be able to plan and mill both femoral and acetabular implant seat. This project aims to combine the advantages of minimally invasive techniques and navigational systems with the accuracy that robotic assisted bone milling can provide. One of the main goals is the study of the technical problems of previous systems and to develop methods to prevent those.

The project-name is RomEo (Robotic minimally invasive Endoprosthetics), the main project partners are the Helmut-Schmidt University/Hamburg and the Department of Trauma and Orthopaedics of the BG Trauma Hospital Hamburg. The paper focuses on:

The determination of forces acting on the femur during milling: The determination of the ideal minimally invasive access route in cadaver operations

The “workspace” created in minimally invasive hip surgery as determined in cadaver operations, including a 3D reconstruction

Possible solutions of the problems of non-invasive patient fixation as determined in cadaver testing with different fixation methods

Feasibility of 3D operation simulation using Voxelman data, access route data and implant CAD data