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| Proper functioning of the hand relies on its capacity to rotate and point the palm upward (i.e. supination) or downward (i.e. pronation) when standing up with the elbow in 90° flexion. Hand rotation is possible because of forearm rotation and also rotation of the whole upper limb at the shoulder. Two distinct mechanisms contribute to hand rotation: one in which the ulna is immobile and another in which the ulna is mobile |
Pronation and supination of the hand: Anatomy and biomechanics - ScienceDirect http://tinyurl.com/y5a7cjjh
