The hamate bone (from

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

hamatus, "hooked"), or unciform bone (from

uncus The uncus is an anterior extremity of the parahippocampal gyrus. It is separated from the apex of the temporal lobe by a slight fissure called the incisura temporalis (also called rhinal sulcus). Although superficially continuous with the hippo ...

'', "hook"), Latin os hamatum and occasionally abbreviated as just hamatum, is a bone in the human

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carp ...

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 A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

. The hamate is found within the distal row of carpal bones, and abuts the

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

s of the

little finger The little finger, or pinkie, also known as the baby finger, fifth digit, or pinky finger, is the most ulnar and smallest digit of the human hand, and next to the ring finger. Etymology The word "pinkie" is derived from the Dutch word ''p ...

and ring finger. Adjacent to the hamate on the ulnar side, and slightly above it, is the

pisiform bone The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisifomis'', pea-shaped), is a small knobbly, sesamoid bone that is found in the wrist. It forms the ulnar border of the carpal tunnel. Structure The pisiform is a sesamoid bone, ...

. Adjacent on the radial side is the

capitate The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third carpomet ...

, and proximal is the

lunate bone The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row carpal bones, which lie between the ulna and radius and the h ...

Surfaces

The hamate bone has six surfaces: * The ''superior'', the apex of the wedge, is narrow, convex, smooth, and articulates with the

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped flake removed from a stone tool during the process of pressure flaking. In the Natufian period, a lu ...

. * 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 A hamus or hamulus is a structure functioning as, or in the form of, hooks or hooklets. Etymology The terms are directly from Latin, in which ''hamus'' means "hook". The plural is ''hami''. ''Hamulus'' is the diminutive – hooklet or little ho ...

, 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

by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments.

Hook

Hamulus of hamate (left hand) - animation02

The ''hook of hamate'' ( la, hamulus) 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. 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 In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the hand. The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue. Normall ...

, 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 The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle of ...

. 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. 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

Clinical significance

The hamate bone is the bone most commonly fractured when a

golf Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standardized playing area, and coping wi ...

er hits the ground hard with a

golf club A golf club is a club used to hit a golf ball in a game of golf. Each club is composed of a shaft with a grip and a club head. Woods are mainly used for long-distance fairway or tee shots; irons, the most versatile class, are used for a variet ...

on the downswing or a hockey player hits the ice with a slap shot. The fracture is usually a

hairline fracture A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or ...

, commonly missed on normal

X-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nbs ...

. Symptoms are pain aggravated by gripping, tenderness over the hamate and symptoms of irritation of the

ulnar nerve In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is ...

. 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 Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding t ...

players. Several professional baseball players have had the bone removed during the course of their careers. This condition has been called "Wilson's Wrist".WILSON JN. Profiles of the carpal canal. ''J Bone Joint Surg Am''. 1954 Jan;36-A(1):127–132 The calcification of the unciform bone is seen on X-rays during puberty and is sometimes used in

orthodontics Orthodontics is a dentistry specialty that addresses the diagnosis, prevention, management, and correction of mal-positioned teeth and jaws, and misaligned bite patterns. It may also address the modification of facial growth, known as dentofacial ...

to determine if an adolescent patient is suitable for orthognathic intervention (i.e. before or at their growth spurt).

Etymology

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

Additional images

File:Hamate bone (left hand) - animation01.gif, Position of hamate bone (shown in red). Left hand. Animation. File:Hamate bone (left hand) - animation04.gif, Hamate bone of the left hand. The hook-like process is called

. Image:Hamate bone.jpg, Hamate bone. File:RightHumanAnteriorDistalRadiusUlnaCarpals - Hamate bone.png, Right hand anterior view (palmar view). Thumb on top. File:RightHumanPosteriorDistalRadiusUlnaCarpals - Hamate bone.png, Right hand posterior view (dorsal view). Thumb on bottom. Image:Gray219 - Hamate bone.png, Bones of the left hand. Palmar surface. Hamate shown in yellow. Image:Gray220 - Hamate bone.png, Bones of the left hand. Dorsal surface. Hamate shown in yellow. Image:Gray422 - Hamate bone.png, Transverse section across the wrist and digits. Hamate shown in yellow. File:Ospoignet - Hamate bone.png, Cross section of wrist (thumb on left). Hamate shown in red. File:Slide1dsds - Hamate bone.png, Right wrist joint. Deep dissection. Anterior (palmar) view.

References

{{DEFAULTSORT:Hamate Bone Skeletal system Wrist Bones of the hand Carpal bones