Upper limb
Hamate bone
Os hamatum
- Origin
- Ulnar bone of the distal row, wedge shaped, with a projecting hook on its palmar side. It meets the capitate, the triquetrum and the bases of the fourth and fifth metacarpals.
- Insertion
- The hook carries the flexor retinaculum, the pisohamate ligament and flexor digiti minimi brevis and opponens digiti minimi.
- Function
- Closes the carpal tunnel on the ulnar side and at the same time forms the radial wall of Guyon canal; the mobile fourth and fifth rays let the palm cup around an object.
- Innervation
- Deep branch of the ulnar nerve (C8-T1)
- Movement & chain
- The fourth and fifth carpometacarpal joints allow ten to thirty degrees of flexion, which lets the palm fold around an object.
- Palpation
- The hook is felt about a centimetre distal and radial to the pisiform, under firm pressure in the heel of the hand.
- Clinical
- Fracture of the hook occurs in golf, tennis and baseball, from the impact of the club or racket handle. It heals poorly and can irritate the little finger tendon and the deep branch of the ulnar nerve, with loss of force in the intrinsic hand muscles.
- Segmental innervation
- C8-T1
- In clinical practice
- In a racket or club sport athlete with ulnar hand pain and weakness, press specifically on the hook; a standard wrist radiograph often misses the fracture.
- Region in the model
- Upper limb