The hamate is one of the carpal bones, forms part of the distal carpal row and has a characteristic hook on its volar surface.
The hamate has a wedge-shaped body. It bears an uncinate (unciform) hamulus (hook of hamate) which projects in a volar fashion from the distal part of its palmar surface. It is the most ulnar based bone within the distal carpal row. It has four surfaces:
- superior surface: apex of the wedge is narrow, convex, and smooth
- inferior surface: concave facets separated by a ridge
- volar surface: hook-like process (hamulus) on the lower and ulnar side
- medial surface: oblong facet
The hamate articulates with five bones: the lunate, capitate, triquetral, fourth metacarpal, and fifth metacarpal:
- proximal thin margin of the wedge articulates with the lunate while the fourth and fifth metacarpals articulate with the base distally
- medial surface is broad and articulates with the triquetrum
- lateral surface articulates with the capitate
- hook of the hamate is distal and radial in relation to the pisiform
- flexor digiti minimi brevis and opponens digiti minimi both arise from the convex surface of the hook of the hamate
- abductor digiti minimi arises from the hook of hamate
- flexor carpi ulnaris inserts via the pisohamate ligament into apex of the hook of hamate
- flexor digitorum profundus uses the hook of hamate as a pulley during flexion of the 5 finger with ulnar deviation
- flexor retinaculum attaches to the apex of the hamulus
- transverse carpal ligament
- pisohamate ligament
- triquetrohamate ligament
- capitohamate ligament
Nearly 100% of hamate specimens have radial artery supply. Most specimens have dual radial and ulnar supply with the ulnar artery contributing a smaller percentage. ~30% have absent ulnar artery supply.
A terminal deep branch of the ulnar nerve lies in a transverse groove underneath the hook of the hamate towards its base.
- bipartite hook of hamate
- os hamuli proprium (incomplete fusion of the ossification center of the hook)
It is the second bone to ossify following the capitate. It is thought to start ossifying by the end of the third month. Fusion is complete by age 14-16.
History and etymology
The term derives from the Latin hamatus meaning hooked.
The hamate may be visualized on a number of series of the distal upper limb including:
Routine PA and lateral views of the wrist potentially miss hamate fractures. Carpal tunnel views, in addition to PA, lateral, and oblique views are typically required when hamate fractures are suspected.
CT has a sensitivity of 100% and a specificity of 94% in visualizing fractures of the hamate compared to x-ray which has a sensitivity of 72% and specificity of 88%.