Pronation and supination: rotatory movements of the forearm at the superior and inferior radio-ulnar joints, turning the palm downward (pronation) or upward (supination) around an oblique axis.
Examined with the elbow semiflexed in the midprone position; palm turns upward in supination, downward in pronation.
Axis and Mechanism of Movement
Axis of rotation: oblique, running from the center of the head of the radius above to the base of the styloid process of the ulna below.
In supination, the radius and ulna lie parallel; in pronation, the lower end of the radius rotates and crosses in front of the lower end of the ulna.