Hamate bone

The hamate bone (from Latin hamatus, "hooked"), or unciform bone (from Latin uncus, "hook"), Latin os hamatum and occasionally abbreviated as just hamatum,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> is a bone in the human wrist readily distinguishable by its wedge shape and a hook-like process ("hamulus") 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.<ref name=GRAYS2005>Template:Cite book</ref>Template:Rp

Adjacent to the hamate on the ulnar side, and slightly proximal and ulnar to it, is the pisiform bone. Adjacent on the radial side is the capitate, and proximal is the lunate bone.<ref name=GRAYS2005 />Template:Rp

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.

Hook

File:Hamulus of hamate (left hand) - animation02.gif

Hamate bone of the left hand. Hamulus shown in red.

The hook of hamate (Template:Langx) is found at the proximal, ulnar side of the hamate bone. The hook is a curved, hook-like process that projects 1–2 mm distally and radially.<ref name=EATHORNE2005>Template:Cite journal</ref> The ulnar nerve hooks around the hook of hamate as it crosses towards the medial side of hand.

The hook forms the ulnar border of the carpal tunnel, and the radial border for Guyon's canal. Numerous structures attach to it, including ligaments from the pisiform, the transverse carpal ligament, and the tendon of flexor carpi ulnaris.<ref name=EATHORNE2005 />

Its medial surface to the flexor digiti minimi brevis and opponens digiti minimi; its lateral side is grooved for the passage of the flexor tendons into the palm of the hand.

Development

The ossification of the hamate starts between 1 and 12 months.<ref name=CHLT>Template:Cite journal</ref> The hamate does not fully ossify until about the 15th year of life.<ref name=EATHORNE2005 />

Other animals

The bone is also found in many other mammals, and is homologous with the "fourth distal carpal" of reptiles and amphibians.

Function

Template:Expand section The carpal bones function as a unit to provide a bony superstructure for the hand.<ref name=GRAYS2005 />Template:Rp

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 fifth digit with partial involvement of the fourth digit 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.<ref name=EATHORNE2005 />

It is also a common injury in baseball players. Several professional baseball players have had the bone removed during the course of their careers.<ref>Template:Cite news</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite news</ref><ref>Template:Cite news</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This condition has been called "Wilson's Wrist".<ref>WILSON JN. Profiles of the carpal canal. J Bone Joint Surg Am. 1954 Jan;36-A(1):127–132</ref>

The calcification of the hamate 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 (i.e. before or at their growth spurt).Template:Cn

Etymology

The etymology derives from the Latin hamatus "hooked," from hamus which means "hook".

Additional images

• Hamate bone (left hand) - animation01.gif

  Position of hamate bone (shown in red). Left hand. Animation.

• Hamate bone (left hand) - animation04.gif

  Hamate bone of the left hand. The hook-like process is called hamulus.

• Hamate bone.jpg

  Hamate bone.

• RightHumanAnteriorDistalRadiusUlnaCarpals - Hamate bone.png

  Right hand anterior view (palmar view). Thumb on top.

• RightHumanPosteriorDistalRadiusUlnaCarpals - Hamate bone.png

  Right hand posterior view (dorsal view). Thumb on bottom.

• Gray219 - Hamate bone.png

  Bones of the left hand. Palmar surface. Hamate shown in yellow.

• Gray220 - Hamate bone.png

  Bones of the left hand. Dorsal surface. Hamate shown in yellow.

• Gray422 - Hamate bone.png

  Transverse section across the wrist and digits. Hamate shown in yellow.

• Ospoignet - Hamate bone.png

  Cross section of wrist (thumb on left). Hamate shown in red.

• Slide1dsds - Hamate bone.png

  Right wrist joint. Deep dissection. Anterior (palmar) view.

See also

• Carpal bone
• Hypothenar hammer syndrome