Fig. 4
From: 3D analysis of the distal ulna with regard to the design of a new ulnar head prosthesis
The center axes are shown and its distance was measured resulting in the ulna offset distance. The ulnar rotation was measured with a plane aligned with the coordinate system, zero being parallel to the red arrow (x-axis). This plane was then pulled into the shaft center, which was also defined as the rotation axis. From there the plane was rotated around the axis resulting in the amount of pro- and supination