The lunate bone (semilunar bone) is a carpal bone in the

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

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 ...

. 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 The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

and

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

and the

. The lunate carpal bone is situated between the lateral scaphoid bone and medial

triquetral The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the ...

bone.

Structure

The lunate is a crescent-shaped carpal bone found within the

. The lunate is found within the proximal row of carpal bones. Proximally, it abuts the

. Laterally, it articulates with the

scaphoid bone The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone is ...

, medially with the triquetral bone, and distally with the

capitate bone 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 ...

. The lunate also articulates on its distal and medial surface with the hamate bone. The lunate is stabilised by a medial ligament to the scaphoid bone and a lateral ligament to the triquetral bone. Ligaments between the radius and carpal bone also stabilise the position of the lunate, as does its position in the lunate fossa of the radius.

Bone

The proximal surface of the lunate bone is smooth and convex, articulating with the radius. The lateral surface is flat and narrow, with a crescentic facet for articulation with the

. The medial surface possesses a smooth and quadrilateral facet for articulation with the triquetral bone. The palmar surface is rough, as is the dorsal surface. The dorsal surface is broad and rounded. The distal surface of the bone is deep and concave.

Blood supply

The lunate receives its blood supply from dorsal and palmar branches.

Variation

The lunate has a variable shape. About one-third of lunate bones do not possess a medial facet, meaning they do not articulate with the hamate bone. Additionally, in about 20% of people, blood supply may arise from palmar vessels alone.

Ossification

The

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

of the lunate bone commences between 18 months and 4 years 3 months.

Function

The carpal bones function as a unit to provide a bony superstructure for the

. As a proximal carpal bone, the lunate is also involved in movement of the wrist.

Clinical relevance

The lunate bone is the most frequently dislocated carpal bone. *

Carpal coalition Carpal coalition is the abnormal fusion of two or more carpal bones when they fail to segment during intrauterine development. First described by Eduard Sandifort in 1779, carpal coalitions are often an isolated issue which connect two carpal bone ...

* Kienbock's disease * Teisen classification

Etymology

The name of the lunate bone derives from the "crescent-shaped" ( la, lunatus), from

Latin Latin (, or , ) is a classical language belonging to the 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 the power of the ...

''luna'' ("moon"), from the bone's resemblance to a crescent moon. In amphibians and reptiles, the bone is instead referred to as the ''intermedium'', because of its position between the other two proximal carpals.

Additional images

File:Lunate bone (left hand) - animation01.gif, Lunate bone of the left hand (shown in red). Animation. File:Lunate bone (left hand) - animation02.gif, Lunate bone of the left hand. Close up. Animation. Image:Lunate bone.jpg, Lunate bone. Image:Gray219 - Lunate bone.png, Bones of the left hand. Volar surface. Image:Gray220 - Lunate bone.png, Bones of the left hand. Dorsal surface. File:Ospoignet - Lunate bone.png, Cross section of wrist (thumb on left). Lunate shown in red. Image:LunatedislocationAP.jpg, Dislocated lunate Image:LunatedislocationL.jpg, Dislocated lunate File:Dissection of the human hand - 02.jpg, Wrist joint. Deep dissection. Posterior view. File:Slide5kaka.JPG, Wrist joint. Deep dissection. Posterior view.

References

Wrist Upper limb anatomy Bones of the hand Carpal bones {{Portal bar, Anatomy