Fig. 1

Experimental setup. The humerus and ulna were solidly fixed on a customized wooden jig with the elbow flexed at 90°. The humerus was set horizontally and ulna was set perpendicularly to the ground. The radius was kept in one of three forearm positions (full pronation, neutral rotation, or full supination) with a 2.0-mm K-wire inserted in the distal radius only to keep forearm rotation. The displacement of the radial head relative to the proximal ulna was measured by an electromagnetic tracking device (trak STAR™; Ascension Technology Corporation, Shelburne, VT, USA). Sensors were inserted into the radial head and the proximal ulna. A cord was positioned around the neck of the radial head to apply load for passive mobility testing