The hamate bone or unciform bone is a bone in the human wrist readily distinguishable by its wedge shape and a hook-like process projecting from its palmar surface.
Structure
The hamate is an irregularly shaped carpal bone found within the hand. The hamate is found within the distal row of carpal bones, and abuts the metacarpals of the little finger and ring finger. Adjacent to the hamate on the ulnar side, and slightly above it, is the pisiform bone. Adjacent on the radial side is the capitate, and proximal is the lunate.
Surfaces
The hamate bone has six surfaces:
The superior, the apex of the wedge, is narrow, convex, smooth, and articulates with the lunate.
The inferior articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge.
The dorsal is triangular and rough for ligamentous attachment.
The palmar presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and laterally.
The medial articulates with the triangular bone by an oblong facet, cut obliquely from above, downward and medialward.
The lateral articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments.
The ossification of the hamate starts between 1 and 12 months. The hamate does not fully ossify until about the 15th year of life.
In animals
The bone is also found in many other mammals, and is homologous with the "fourth distal carpal" of reptiles and amphibians.
Function
The carpal bones function as a unit to provide a bony superstructure for the hand.
Clinical significance
The hamate bone is the bone most commonly fractured when a golfer hits the ground hard with a golf club on the downswing or a hockey player hits the ice with a slap shot. The fracture is usually a hairline fracture, commonly missed on normal X-rays. Symptoms are pain aggravated by gripping, tenderness over the hamate and symptoms of irritation of the ulnar nerve. This is characterized by numbness and weakness of the pinkie finger with partial involvement of the ring finger as well, the "ulnar 1½ fingers". The hook of hamate is particularly prone to fracture-related complications such as non-union due to its tenuous blood supply. It is also a common injury in baseball players. Several professional baseball players have had the bone removed during the course of their careers. This condition has been called "Wilson's Wrist". The calcification of the unciform bone is seen on X-rays during puberty and is sometimes used in orthodontics to determine if an adolescent patient is suitable for orthognathic intervention.
Etymology
The etymology derives from the Latinhamatus "hooked," from hamus which means "hook".
