Fetlock is the common name in

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

s, large animals, and sometimes dogs for the

metacarpophalangeal The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

and

metatarsophalangeal The metatarsophalangeal joints (MTP joints), also informally known as toe knuckles, are the joints between the metatarsal bones of the foot and the proximal bones (proximal phalanges) of the toes. They are condyloid joints, meaning that an ellipt ...

joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...

s (MCPJ and MTPJ). Although it somewhat resembles the human

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular join ...

in appearance, the joint is homologous to the ball of the foot. In anatomical terms, the

hoof The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rumin ...

corresponds to the

toe Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plan ...

, rather than the whole foot.

Etymology and related terminology

The word literally means "foot-lock" and refers to the small tuft of hair situated on the rear of the fetlock joint.Merriam-Webster: fetlock
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Feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...

" refers to the particularly long, luxuriant hair growth over the lower leg and fetlock that is characteristic of certain breeds.

Formation

A fetlock (a MCPJ or a MTPJ) is formed by the junction of the third

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 ...

(in the forelimb) or

metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...

(in the hindlimb) bones, either of which are commonly called the

cannon bone Good conformation in the limbs leads to improved movement and decreased likelihood of injuries. Large differences in bone structure and size can be found in horses used for different activities, but correct conformation remains relatively simil ...

s, proximad and the proximal phalanx distad, commonly called the

pastern The is a part of the leg of a horse between the fetlock and the top of the hoof. It incorporates the long pastern bone (proximal phalanx) and the short pastern bone (middle phalanx), which are held together by two sets of paired ligaments to fo ...

bone. Paired proximal

sesamoid bones In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be prese ...

form the joint with the palmar or plantar distal surface of the third metacarpal or metatarsal bones, and are rigidly fixed to the proximo-palmar or -plantar edge of the proximal phalanx.

As a hinge joint

The fetlock is a

hinge joint A hinge joint (ginglymus or ginglymoid) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having ...

(), allowing

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

and

extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...

, but only allowing minimal

rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...

adduction Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

, or abduction.

Anatomy compared to that of humans

While sometimes the fetlock is colloquially referred to as an "ankle", even by horse experts, that terminology is not correct. The fetlock is a

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

which corresponds to the human upper knuckle, such as that on the

ball A ball is a round object (usually spherical, but can sometimes be ovoid) with several uses. It is used in ball games, where the play of the game follows the state of the ball as it is hit, kicked or thrown by players. Balls can also be used f ...

of the foot.

Problems with the fetlock

Windpuff Good conformation in the limbs leads to improved movement and decreased likelihood of injuries. Large differences in bone structure and size can be found in horses used for different activities, but correct conformation remains relatively simil ...

s *

Sesamoiditis Sesamoiditis is inflammation of the sesamoid bones. Humans Sesamoiditis occurs on the bottom of the foot, just behind the big toe. There are normally two sesamoid bones on each foot; sometimes sesamoids can be bipartite, which means they each ...

Osselet Osselet is arthritis in the fetlock joint of a horse, caused by trauma. Osselets usually occur in the front legs of the horse, because there is more strain and concussion on the fetlock there than in the hind legs. The arthritis will occur at the ...

In thoroughbred race horses, the fetlock is involved in roughly 50% of catastrophic racing injuries.{{cite web, last1=Marquardt, first1=Lucas, title=Is this the death of synthetic racing?, url=http://www.thoroughbreddailynews.com/pdf/magazine/Synthetics-Aug2014.pdf, website=thoroughbreddailynews.com, access-date=9 August 2016

References

*Dyce KM, Sack WO, Wensing CJG. ''Textbook of Veterinary Anatomy'' (2nd Ed.). W.B. Saunders, 1996, p. 591. Horse anatomy