Upper limb
Pisiform bone
Os pisiforme
- Origin
- Sesamoid bone in the tendon of flexor carpi ulnaris, lying on the palmar side of the triquetrum. It carries no weight and is the only carpal bone entirely outside the carpal arch.
- Insertion
- Attachment for the pisohamate and pisometacarpal ligaments and for abductor digiti minimi; the flexor retinaculum spans across it.
- Function
- Lengthens the lever arm of flexor carpi ulnaris and forms the ulnar wall of Guyon canal.
- Innervation
- Ulnar nerve (C8-T1)
- Movement & chain
- With a relaxed wrist it slides sideways under the finger across the triquetrum; with the wrist flexor tensed it is fixed.
- Palpation
- The hard lump in the ulnar corner of the palmar wrist crease, movable sideways when the wrist is relaxed.
- Clinical
- Pisotriquetral osteoarthritis causes pain on leaning through the palm. A fracture follows a direct blow to the heel of the hand and is easily missed on a plain film. In Guyon canal the ulnar nerve beside it may be compressed, giving tingling in the ring and little finger.
- Segmental innervation
- C8-T1
- In clinical practice
- In cyclists and wheelchair users with tingling in the little finger, check this area, because the pressure lands exactly here.
- Region in the model
- Upper limb