Page 178 - Anatomy and Physiology of Farm Animals, 8th Edition

The Equine Foot and Passive Stay Apparatus / 163

The structure of the joints between the wall, ungual cartilages, digital cushion, and
phalanges and between the cannon and prox-
frog. As the frog strikes the ground, both
VetBooks.ir imal phalanx is typical of synovial joints (see the digital cushion and the frog are com-
Chapter 6). The joint cavity of the fetlock is
pressed, widening and thinning them.
especially voluminous to accommodate the Pressure on the bars, the ungual cartilages,
wide range of motion in this ginglymus joint. and the wall spreads the heels and forces
Part of the joint cavity extends proximad blood out of the vascular bed of the foot.
between the cannon bone and suspensory The direct cushioning effect of the frog
ligament. Accumulation of excess synovial and digital cushion is enhanced by the
fluid within this palmar (plantar) recess resiliency of the wall and the hydraulic
may be associated with the trauma of hard shock‐absorbing effect of the blood in the
training. This produces a visible distension of hoof. At the same time that the hoof is
the recess called wind puffs or wind galls. spread by frog pressure, blood is forced out
of the vascular structures of the foot, which
not only absorbs concussion but also
Function pumps blood out of the foot and into the
veins of the leg against gravity. This pump-
The functions of the foot are to aid in effi- ing action of the foot is an important means
cient locomotion and provide standing of returning venous blood from the foot to
support. The single toe of the horse is a the general circulation.
highly adapted aid to efficient gait, as the Horses confined to a stall or other-
foot absorbs concussion, stores energy in wise immobilized for extended periods
its elastic tissues, and provides leverage for are often deprived of the pumping ben-
muscles that insert on the bones within it. efits of the active foot, with the result
Likewise, the famous ability of horses to that tissue fluid accumulates in the dis-
sleep while standing owes itself primarily tal limb. This gives the appearance of
to the ligamentous structures of the foot swelling, which is colloquially referred
and other more proximal parts of the limb. to as stocking up, in the pasterns, fet-
locks, and sometimes even more proxi-
mal. The swelling, however, is not due to
Concussion and Storage of Energy inflammation, is not painful, and very
quickly resolves when the horse is
A large part of the mechanism for absorb- encouraged to exercise for a time.
ing concussion depends on angulation of Flexibility of the hoof is also an impor-
the joints of the limbs at the time of impact tant consideration in correct shoeing.
and immediately following contact of the For most purposes, the shoe should be
foot with the ground. The muscles, ten- nailed only as far back as the quarters so
dons, and ligaments act as springs that that the heels are free to expand over the
absorb the shock of impact by permitting top of the shoe. For the same reason, most
some flexion of the shoulder and elbow and farriers apply shoes that are slightly wider
physiologic hyperextension of fetlock, pas- in the heel than the foot to which they are
tern, and coffin joints. Some of the energy affixed. By this means, the expanding
of the foot striking the ground is stored as heels of the hoof are able to spread and
ligamentous and tendinous structures still maintain contact with the shoe.
stretch; this energy is released as the foot
leaves the ground. The rebound of liga-
ments and tendons straightens the joints Stay Apparatus
and aids in lifting the foot, so that very little
energy is expended on these parts of gait. Ligamentous structures that store and
The hoof and its contents absorb con- release energy during locomotion are also
cussion because of the elasticity of the hoof found proximal to the foot. These elements