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 yea ...

s, large animals, and sometimes dogs for the metacarpophalangeal 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 ellipti ...

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 joi ...

in appearance, the joint is homologous to the

ball of the foot The ball of the foot is the padded portion of the sole between the toes and the arch, underneath the heads of the metatarsal bones. In comparative foot morphology, the ball is most analogous to the metacarpal (forepaw) or metatarsal (hindpaw) ...

. 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 rum ...

corresponds to the toe, 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 premie ...

" 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 ar ...

(in the forelimb) or metatarsal (in the hindlimb) bones, either of which are commonly called the cannon bones, proximad and the proximal phalanx distad, commonly called the pastern bone. Paired proximal sesamoid bones 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 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 * Ext ...

, 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, or

abduction Abduction may refer to: Media Film and television * "Abduction" (''The Outer Limits''), a 2001 television episode * " Abduction" (''Death Note'') a Japanese animation television series * " Abductions" (''Totally Spies!''), a 2002 episode of an ...

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 ...

which corresponds to the human upper

knuckle The knuckles are the joints of the fingers. The word is cognate to similar words in other Germanic languages, such as the Dutch "knokkel" (knuckle) or German "Knöchel" (ankle), i.e., ''Knöchlein'', the diminutive of the German word for bone ( ...

, 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 c ...

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