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 mi ...

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

metatarsophalangeal The metatarsophalangeal joints (MTP joints) are the joints between the metatarsal bones of the foot and the proximal bones (proximal phalanges) of the toes. They are analogous to the knuckles of the hand, and are consequently known as toe knuck ...

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, 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 joint. The ...

in appearance, the joint is homologous to the ball of the foot. In anatomical terms, the hoof corresponds to the toe, rather than the whole human 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
/ref> "

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 an exa ...

" 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 the forelimb) or metatarsal (in the hindlimb) bones, either of which are commonly called the cannon bones, proximally and the proximal phalanx distally, 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 tightly attached 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 where 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 o ...

(), allowing

flexion Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

and extension, but only allowing minimal

rotation Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...

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 relativ ...

, or abduction.

Anatomy compared to that of humans

While the fetlock is sometimes colloquially referred to as an "ankle", even by horse experts, that terminology is misleading. The ankle joint in humans corresponds to the hock of horses. The fetlock is a metacarpo- or metatarsophalangeal joint which corresponds to the human upper knuckle, such as that on the ball of the foot. This usage likely originated from early definitions of "ankle" as "between foot and leg" derived from the common root of "angle" meaning to bend.

Problems with the fetlock

Windpuff The limbs of the horse are structures made of dozens of bones, joints, muscles, tendons, and ligaments that support the weight of the equine body. They include three apparatuses: the suspensory apparatus, which carries much of the weight, preve ...

s * Sesamoiditis * Osselet 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