The carpal bones, or carpals, are a group of eight small and irregularly shaped bones that are found within the wrist. They are located between the bones of the forearm (radius and ulna) and the metacarpal bones. The carpal bones are organized into two rows - a proximal row and a distal row. Each row contains four carpal bones.

The carpal bones are classified as short bones (Latin: ossa brevia). Besides the hand, the short bones are also found within the foot (tarsal bones). Each carpal bone has its unique shape and features that serve to provide specific functions.

The proximal row, as viewed from the radial to ulnar side, includes the following carpal bones:

Scaphoid (Read more!) - boat-shaped bone that forms the radial border of the proximal row; it articulates with the radius;
Lunate (Read more!) - crescent-shaped bone that also articulates with the radius;
Triquetral (Read more!) - pyramidal-shaped bone; it is also called the triquetrum;
Pisiform (Read more!) - pea-shaped bone that lies on the triquetral and articulates with it; this bone is embedded within the tendon of the flexor carpi ulnaris.

The distal row of the carpal bones, also viewed from the radial to ulnar side, includes the following:

Trapezium (Read more!) - saddle-shaped bone that is found between the scaphoid and the base of the first metacarpal; forms the radial border of the distal row;
Trapezoid (Read more!) - boot-shaped bone; the smallest bone in the distal row;
Capitate (Read more!) - the largest and most central carpal bone; it bears the largest amount of articular surfaces;
Hamate (Read more!) - irregularly shaped bone that can be easily distinguished by its hook-like projection.

Each side of the wrist is slightly elevated, and the carpal bones and their features primarily form these elevations. The pisiform bone and the hook of the hamate are found on the ulnar side, while the tubercle of the scaphoid and the tubercle of the trapezium are found on the radial side of the palm. Between these bones is a groove - carpal groove.

A fibrous band called the flexor retinaculum stretches over the carpal groove and attaches to the mentioned carpal projections, forming the carpal tunnel. The median nerve and nine flexor tendons (tendons of the flexor pollicis longus, flexor digitorum profundus, and flexor digitorum superficialis) pass through the tunnel, entering the hand.

Note: Several mnemonics can help to remember the carpal bones and their sequence. Mnemonics “So Long To Pinky, Here Comes The Thumb” or “Straight Line To Pinky, Here Comes The Thumb” name all the carpal bones in a circle. The circle starts with the radial side of the proximal row and goes opposite the clockwise direction. Mnemonics like “Some Lovers Try Positions, That They Cannot Handle” and “She Likes To Play, Try To Catch Her” describe the position of the carpal bones from the radial to the ulnar side of the hand. The first part is for the proximal row, while the part after the comma corresponds to the distal row.

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Carpal bones