The wrist rotates primarily through the movement of two bones in the forearm: the radius and ulna. The radius, the larger of the two bones, forms a joint with the scaphoid and lunate bones in the wrist. This joint allows the wrist to move and rotate.
Here's a breakdown of the wrist's rotation:
- Pronation: When the palm faces downwards, the radius rotates over the ulna, bringing the thumb inward.
- Supination: When the palm faces upwards, the radius and ulna are parallel, allowing the thumb to point outwards.
These movements are facilitated by several muscles, ligaments, and tendons surrounding the wrist joint. The specific muscles involved in pronation and supination include:
- Pronator teres: This muscle helps turn the palm down (pronation).
- Pronator quadratus: This muscle also assists in pronation.
- Supinator: This muscle helps turn the palm up (supination).
- Biceps brachii: This muscle, primarily involved in elbow flexion, also contributes to supination.
The wrist's ability to rotate allows for a wide range of movements and activities, from writing and typing to playing sports.
