Anatomy · Bones

Carpal bones

Eight bones in two rows

Wrist · base of the hand

The carpal bones are the eight small bones of the wrist, arranged in two rows of four between the forearm bones and the metacarpals. From the thumb side the proximal row is scaphoid, lunate, triquetrum and pisiform, and the distal row is trapezium, trapezoid, capitate and hamate. Together they form a U-shaped arch, the floor and walls of the carpal tunnel.

How to spot them

▸A compact cluster of eight small, irregular bones between the forearm bones and the palm, in two rows of four
▸Proximal row from the thumb side: scaphoid, lunate, triquetrum, pisiform; distal row from the little finger back to the thumb: hamate, capitate, trapezoid, trapezium
▸The pisiform is a small pea-shaped bump on the palm side at the little-finger edge; the hook of the hamate projects forward beside it
▸Form a concave arch on the palm side, roofed by the flexor retinaculum to make the carpal tunnel

What to know

Eight small bones arranged in two rows of four, joining the forearm to the palm

Carpal bones — the bones of the wrist.

The mnemonic 'So Long To Pinky, Here Comes The Thumb' names them in order, starting on the thumb side

Carpal bones — scaphoid, lunate, triquetrum, pisiform; hamate, capitate, trapezoid, trapezium.

Their names mean boat, moon, three-cornered, pea, table, table-like, head and hook

Carpal bones — scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate.

Together they form a concave arch whose floor and walls, roofed by a strong ligament, carry the median nerve and nine tendons into the hand

Carpal bones — the carpal tunnel.

The end of the medial forearm bone never touches them directly, a cartilage disc intervening, so only three of the four in the proximal row take part in the wrist joint

Carpal bones — the scaphoid, lunate and triquetrum contribute to the radiocarpal joint.

The order in which their ossification centres appear, from the capitate in infancy to the pea-shaped bone at around twelve, is used to judge a child's bone age

Carpal bones — hand and wrist X-rays are used to assess skeletal maturity.

Of these, the largest is the head-shaped bone in the centre of the wrist, and the smallest the pea-shaped one

Carpal bones — capitate (largest) and pisiform (smallest).

Key ideas

The two rows articulate with each other at the midcarpal joint; together with the radiocarpal joint, this produces all wrist movement.
The flexor retinaculum spans the arch, attaching to the scaphoid and trapezium on the thumb side and the hamate and pisiform on the little-finger side.

Quick-fire facts

•There are eight carpal bones; the foot has seven tarsal bones.
•Mnemonics: 'So Long To Pinky, Here Comes The Thumb' (OpenStax) and 'She Likes To Play Try To Catch Her' (Kenhub) both list the bones in the same order.
•The scaphoid is the most commonly fractured carpal bone, usually after a fall on the outstretched hand.
•The pisiform is a sesamoid bone in the tendon of flexor carpi ulnaris, and the hook of the hamate lies next to the ulnar nerve in Guyon's canal.
•The capitate is the largest carpal bone; it sits at the centre of the wrist and articulates with the third metacarpal.
•Nine tendons (four of flexor digitorum superficialis, four of flexor digitorum profundus, and flexor pollicis longus) and the median nerve pass through the carpal tunnel.
•Ossification centres appear from about the first year (capitate) to about twelve years (pisiform), in a rough anticlockwise order from the capitate.
•The word 'carpus' is from the Greek karpos, the wrist.

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Sources

OpenStax — Anatomy and Physiology 2e — 8.2 Bones of the Upper Limb
Kenhub — Carpal bones