The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the

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 carpal ...

on the medial side of the proximal row of the carpus between 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 lithic flake, flake removed from a stone tool during the process of pressure flaking. In the Natufian cu ...

and

pisiform The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisiformis'', 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, ...

bones. It is on the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

r side of the hand, but does not directly articulate with the

. Instead, it is connected to and articulates with the ulna through the Triangular fibrocartilage discManaster, B. J., Julia Crim "Imaging Anatomy: Musculoskeletal E-Book" Elsevier Health Sciences, 2016, p. 326. and ligament, which forms part of the ulnocarpal joint capsule. It connects with the

hamate The hamate bone (from Latin language, Latin wiktionary:hamatus, hamatus, "hooked"), or unciform bone (from Latin language, Latin ''wikt:uncus, uncus'', "hook"), Latin os hamatum and occasionally abbreviated as just hamatum, is a bone in the huma ...

, and

bones. It is the 2nd most commonly fractured carpal bone.

Structure

The triquetral is one of the eight

carpal bone The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In hu ...

s of 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#Characteristics, koala (which has two thumb#O ...

. It is a three-faced bone found within the proximal row of carpal bones. Situated beneath the

, it is one of the carpal bones that form the carpal arch, within which lies the

carpal tunnel In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor ( palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the ...

. The triquetral bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. To facilitate its palpation in an exam, the hand must be radially deviated so that the triquetrium moves out from under the ulnar styloid process. The triquetrum may be difficult to find, since it also lies under the pisiform. The triquetral bone has nutrient foramina for entering the nutrient vessels into the bone which comes from branches of the radial, ulnar, and interosseous arteries.

Ossification

The triquetral bone ossifies between 9 months and 50 months (4 years and 2 months).

Surfaces

The ''superior surface'' presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist. The ''inferior surface'', directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments. The ''volar surface'' presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment. The ''lateral surface'', the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate. The ''medial surface'', the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist.

In animals

In reptiles and amphibians, the bone is instead referred to as the ''ulnare'', since (at least in the most primitive fossils) it articulates with the

Function

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

Fracture

Triquetral fractures can occur due to forceful flexion of the wrist, causing an avulsion of the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

aspect of the bone that is often hidden on anterior radiographs, but can be seen as a tiny bone fragment on

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

views.

Etymology

The etymology derives from the Latin ''triquetrus'' which means "three-cornered." Therefore, it is sometimes also called the triangular bone or os triangulare. However, ''os triangulare'' may also refer to a nearby

accessory bone An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a anatomical variation, variant in a significant number of people. It poses a risk of being misdiagnosis, misdiagnosed as bone fracture ...

Additional images

File:Triangular bone (left hand) - animation01.gif, Triquetral bone of the left hand (shown in red). Animation. File:Triangular bone (left hand) - animation02.gif, Triquetral bone of the left hand. Close up. Animation. File:Triquetral bone.jpg, Triquetral bone. File:RightHumanPosteriorDistalRadiusUlnaCarpals - Triquetral bone.png, Right hand posterior view (dorsal view). Thumb on bottom. File:RightHumanAnteriorDistalRadiusUlnaCarpals - Triquetral bone.png, Right hand anterior view (palmar view). Thumb on top. File:Gray219 - Triangular bone.png, Bones of the left hand. Palmar surface. Triquetral shown in yellow. File:Gray220- Triangular bone.png, Bones of the left hand. Dorsal surface. Triquetral shown in yellow. File:Ospoignet - Triquetral bone.png, Cross section of wrist (thumb on left). Triquetral shown in red. File:Dorsale Triquetrumabsprengung - CT VRT with arrow.png, Triquetral fracture indicated by the white arrow. File:TriQFracture.PNG, Triquetral fracture as seen on lateral view of a radiograph.