Pro- and supination motion of the forearm. Influence of the articulatio humeroulnaris

The development of a kinematic model of the pro- and supination, that can b e used to predict the influence of angulations of ulna and radius on the pr onation and supination is based on the precise knowledge of the pronation a nd supination movement. We performed two parallel studies for examining the pronation and supination motion of the human forearm. The first experiment dealt with MRI-studies on 18 probands (36 examined forearms). As a result we observed an evasive movement of the ulna during the rotation of 7,14 deg rees medial. In order to prove whether the evasive movement was ca used by a rotation of the humerus or by an evasion in the articulatio humeroulnaris, we carried out a second experiment, using 30 preparations. The measurement of the pro- and supination motion with a fixed humerus was expedited using a special e xperimental setup which guaranteed that the ulna could move freely. In all cases we found the same magnitude of the evasive motion of the ulna. Therefore we demonstrated,that the ulna performs an evasive motion during t he pro- and supination motion of the forearm that influences the kinematic behavior of the pro- and supination motion significantly.