Page 118 - Anatomy and Physiology of Farm Animals, 8th Edition

Joints / 103

Cartilaginous Joints cartilages, articular cavity, joint capsule,
VetBooks.ir The bones of a cartilaginous joint are and ligaments (Fig. 6‐2).
The articular surfaces are specialized
united by cartilage, with no intervening
joint cavity. These, too, are relatively immo- layers of compact bone on the surfaces that
articulate with other bones.
bile; the presence of cartilage provides The articular cartilage is a layer of hya-
some cushioning and absorbs compressive line cartilage covering the articular surface.
energy when under load. The articular cavity is a space between
A synchondrosis is an immovable joint the adjacent bones of the joint surrounded
in which the uniting medium is hyaline by the joint capsule. Because the space is
cartilage. The union of the diaphysis and normally very small and has within it only
epiphysis of an immature bone (its physis a very small amount of lubricating fluid, it
or growth plate) is an example of synchon- is called a potential space. Inflammation
drosis (Fig. 6‐1). can expand the space with accumulation of
A symphysis (fibrocartilaginous joint) is fluid, a condition called joint effusion.
united by fibrous tissue and cartilage as The joint capsule consists of two com-
found between the two halves of the pelvis ponents. The deeper layer is the synovial
and between the bodies of adjacent verte- membrane (synovium), a delicate layer of
brae. These latter are sufficiently unique specialized connective tissue extending
to merit their own particular name: from the edges of the articular cartilages of
intervertebral disks. the adjacent bones but not covering the
The fibrous or cartilaginous tissues sepa- articular cartilage. This membrane secretes
rating adjacent bones in syndesmoses, syn- the synovial fluid (synovia), which
chondroses, and symphyses can be replaced lubricates the normal joint. The synovial
by bone as a result of either aging or degen- membrane’s surface area may be increased
erative processes. When this occurs, the by folds (plicae synoviales), which may
joint may be called a synostosis. contain fat pads, that project into the joint
cavity. Villi (villi synoviales), which are
Synovial Joints fingerlike projections, may also project
into the joint cavity.
Most synovial (formerly called diarthro- The superficial layer of the joint capsule
dial) joints have similar general structure, is the fibrous capsule, a heavier fibrous
which includes articular surfaces, articular sleeve adjacent to the synovial membrane.

Periosteum
Articular cartilage

Articular cavity
(synovial cavity) Villi Intracapsular
ligament

Meniscus
Synovial
membrane

Fibrous capsule

Figure 6-2. Synovial joints. In these figures, the heavy black line represents the synovial membrane.
Note that it does not cover the articular cartilage or menisci, although it does surround the intracapsular
ligaments. The fibrous capsule is continuous at its attachments with the periosteum of the bones.