How do pronation and supination change the position of the hand?

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Medical illustration of a human knee joint in a parasagittal section just lateral to the midline, labeling ligaments, cartilage, meniscus, patella, synovial structures, and surrounding muscles and fat pads. — joint The ligaments and cartilage in a knee joint.

Pronation and supination are complex twisting motions of the forearm that significantly alter the position of the hand by rotating the radius around the ulna.123

These movements change the hand's orientation as follows:

Supination: The radius and ulna are positioned parallel to each other. In this state, the palm of the hand faces forward, and the thumb is directed away from the body.2
Pronation: The radius and ulna cross one another. In this state, the palm faces toward the rear, and the thumb is positioned next to the body.2

This rotational capability, which allows the palm to turn through an arc of 180°, depends on the specific arrangement of forearm muscles and the structure of the wrist joint.3