Definition of the Elbow Axis for the use of a Hinged Early Motion Elbow Fixator Based on the Subchondral Cortex Compared to the Cartilage Covered Contour

The application of a hinged early motion fixator in the injured elbow joint requires a precise alignment of the technical fixator hinge joint with the flexion and extension axis of the elbow joint. The currently used approach defining the joint center is based on the subchondrale bone layer of Trochlea and Capitulum. While the intraoperatively use of an image intensifier allows to identify the circular shape of the joint line, the true, cartilage covered joint surface is invisible. Fifteen specimens were used to investigate the potential differences between the joint center based on the cartilage surface compared to the center defined by the subchondrale bone layer. The joint centers was analysed on plastinated slices cut out of the center of Trochlea and Capitulum. The clearly visible differences of the cartilage based versus bone based joint centers in the slices proved to be so small that they did not show a statistical significance. Compared to the movement of the joint axis during flexion and extension they do not play an important role and can be neglected. The currently used operative technique based on the visible bone surface is therefore a reliable estimation of the true joint center