The wrist connects the hands to the forearm and allows for the range of motion of the hand. The wrist joint allows flexion, extension and side-to-side deviation. The pronation and supination of the arm (flipping the hand over) is due to the action of the bones in the forearm. The wrist is composed of the joints between the radius and the carpal bones, the carpal bones and the metacarpals, and the joints between the carpal bones themselves.
Radius
The radius is one of the long bones of the forearm. It is largest at the wrist where it articulates with the scaphoid and lunate bones in the radiocarpal joint. This is a condyloid type joint that allows for most of the range of motion of the wrist.
Proximal Carpal Bones
The carpal bones are two rows of small bones that are closely packed in two rows. The bones that are closest to the forearm (proximal to the body) form a row that articulates with the next row of bones allowing support and stability to the hand. There bones in order from the thumb side to the little finger side are: the scaphoid, lunate, triquetrium and pisiform. The scaphoid and pisiform are connected by the flexor retinaculum helping to form the carpal tunnel.
Distal Carpal Bones
The distal (farthest from the arm) carpal bones form a joint with the proximal carpals and the metacarpals on either side. These bones are, from the thumb to the little finger, are the trapezium, trapezoid, capitate and hamate bones. The trapesium, or trapezoid bone, has a saddle joint with the metacarpal of the thumb which allows for the wide range of motion that the thumb exhibits. The hammate bone has a hook that anchors the flexor retinaculum on the little finger side of the palm.
The Metacarpals
The metacarpals, like the raduis, are not actually part of the wrist but are the distal portion of where the wrist articulates. These bones resemble finger bones (phalanges) but are internal to the palm of the hand.
References
- "Gray's Anatomy: Anatomical Basis of Clinical Practice;" Susan Standring; 2008
- "Trail Guide to the Body: How to Locate Muscles, Bones and More;" Andrew Biel; 2005
