Pisiform

The pisiform is a pea-sized bone embedded in the tendon of the flexor carpi ulnaris muscle at the front of the wrist — a sesamoid bone, formed inside a tendon like the kneecap. It sits on the triquetrum and acts as a small pulley, increasing the leverage of the wrist's flexor muscle on the little-finger side.

Key facts

The pisiform is a sesamoid bone, formed within a tendon.
It is the smallest carpal bone.
It can be felt as a small bump at the heel of the hand on the little-finger side.
It increases the mechanical advantage of the flexor carpi ulnaris.
The ulnar nerve passes just beside it in Guyon's canal.

What can go wrong

The pisiform can be bruised or fractured by a fall onto the heel of the hand, though this is uncommon. More famously, the ulnar nerve passing right next to it can be compressed — classically in cyclists leaning on handlebars — causing numbness in the ring and little fingers.

Related procedures & tests

X-ray (general)

Related symptoms

Related muscles

Frequently asked questions

Why is there a bone inside a tendon?

Sesamoid bones grow where a tendon wraps around a joint; they protect the tendon from wear and improve its leverage, like the kneecap does for the thigh muscle.

Can you live without a pisiform?

Yes — it is occasionally removed for arthritis or persistent pain, with surprisingly little loss of wrist function, because its role is a modest mechanical one.

Educational information only. This atlas explains normal anatomy and describes conditions in general terms; it is not medical advice and does not replace assessment by a qualified clinician. If you have symptoms that worry you, seek medical care.