Page 132 - Anatomy and Physiology of Farm Animals, 8th Edition

Joints / 117

In the horse, movement between adjacent one or more of the segments making up a
Fractures, or breaks of bones, may affect
tarsal bones is limited to a very small degree
VetBooks.ir of gliding. However, in the ox, sheep, and joint. Fractures within or close to a joint
are often difficult to reduce adequately,
pig, the proximal intertarsal joint has some
hinge movement. Distal to the hock, the since even minor discontinuities in the
joints are similar to those of the forelimb. articular surface can lead to severe arthritic
changes. Immobilization following reduc-
tion is also often difficult because of the
Pathology of Joints and Related short length of at least one of the segments.
Structures A sprain is a condition in which the
ligaments are stretched, but the joint is not
Since synovial joints depend on free move- persistently subluxated following removal
ment for effective functioning, anything of the displacing force. The term strain is
that interferes with their mobility can pro- sometimes used in place of sprain, although
duce gait abnormalities. Disorders affecting strain is used more frequently to denote
joints are commonly due to injuries, infec- excessive stretching of a muscle or tendon.
tions, or inflammations. Although a considerable amount of swelling
A dislocation, also known as a luxation, may follow a sprain, the affected joint usually
is a condition in which articular surfaces recovers spontaneously if rested adequately.
undergo a significant loss of congruency Lacerations such as those from barbed
(less severe dislocations are subluxations). wire may extend into a joint cavity, causing
Dislocation of a joint nearly always includes loss of synovial fluid and exposing the
stretching or tearing of ligaments, and if interior of the joint to the external envi-
the dislocation is severe enough, the joint ronment. An injury of this nature is serious
capsule also may tear. The usual treatment and may be difficult to treat. The danger is
for dislocation consists of replacing the not from the loss of synovial fluid (which
joint in its normal position (“reducing” the is rapidly replaced), but from infection of
luxation), surgical repair of severely dis- the joint cavity. Synovial fluid is a good
rupted elements if necessary, and external medium for bacterial growth, and the many
support and/or fixation during healing. recesses of most joint cavities make drainage
Reduction may be difficult unless the ani- and treatment of an infected joint difficult.
mal is fully anesthetized so that all muscles There is danger of permanent damage to
are relaxed. Early treatment is important to the articular cartilage from infection.
prevent the joint cavity from filling with Puncture wounds to joints may also
connective tissue. Because of the excessive result from penetration by a sharp object
stretching or tearing of ligaments, recovery such as a nail, wire, or wood sliver. Such
from a dislocation may be less satisfactory wounds are especially dangerous; since the
and take longer than recovery from a wound is often not obvious, it usually
properly treated fracture. drains poorly, and the environment into
Occasionally, a reasonably functional which the bacteria are introduced is fre-
joint, called a false joint, may develop at quently anaerobic (not exposed to air). In
the site of a chronic luxation. In a false such conditions, a puncture wound can
joint, the fibrous connective tissue that precipitate a particularly severe infection.
develops in response to the inflammation Infection may also reach the joint by way
and abnormal stresses at the luxation may of blood or lymph. For example, Erysipelas
provide enough stability to permit consid- of swine and umiblical infections arising
erable movement, even though no joint from a variety of bacteria in foals fre-
capsule or cartilage develops as in true quently result in joint infections. Certain
joints. False joints may also form at a frac- viral illnesses, for example caprine arthritis–
ture site if the ends of the fracture are not encephalitis (CAE) virus of goats, can cause
immobilized. nonseptic arthritis of multiple joints.