Radiographic determinants of the elbow rotation axis: Experimental identification and quantitative validation

This study identifies new radiographic indices to approximate the location of the elbow rotational axis. With use of electromagnetic motion tracking s ource data, the average rotational axis of the ulnohumeral articulation was calculated in seven cadaveric specimens. Quasi-lateral radiographs of the elbow specimens were then analyzed to identify radiographic landmarks of th e elbow axis in the lateral view. The spatial relationships of these landma rks with the elbow aligned on-axis were contrasted with their relationships in eight distinct off-axis alignments. Elbow axis orientation in the trans verse plane (internal/external rotation) was identified by the location of a dense intramedullary cortical line, appearing in the projection of the di stal humerus in relation to the periosteal surface of the posterior cortex of the humerus. This intramedullary line corresponds to the posteromedial c ortex of the distal humerus. Correct alignment occurred when this line laid 27.1 +/- 3.7% of the anteroposterior humeral diameter anterior from the pe riosteal surface of the posterior cortex. Axis orientation in the coronal p lane (abduction/adduction) was identified by the concentric appearance of r adiographic arcs formed by the capitellum, trochlear sulcus, and medial tro chlear flange. Using these radiographic indices. three orthopaedic surgeons were able to fluoroscopically align the elbow along the axis of rotation w ith an accuracy of 3.7 +/- 1.8 degrees. These results are immediately appli cable to fluoroscopic identification of the elbow axis. This technique can be used to increase the accuracy of hinge placement during application of h inged external fixation or distraction arthroplasty.