Page 345 - The Veterinary Care of the Horse

a proteoglycan matrix and water. The collagen fibrils give tensile strength and structural

support to the articular cartilage. The proteoglycan matrix compresses a little to allow
VetBooks.ir distribution of the load during weight bearing. When the cartilage is compressed, a thin film
of water is squeezed from the matrix onto the surface of the cartilage and this keeps the

cartilage surfaces apart and is important for lubrication of the joint. When the joint is no
longer under pressure and the cartilage expands, the water is pulled back into the matrix. The

cells responsible for producing cartilage are called chondrocytes; these make up only 2% of
the tissue volume.

Articular cartilage has no blood vessels or nerves. It relies on synovial fluid for nutrition.
Nerve endings in the joint capsule, ligaments, muscles and subchondral bone give rise to pain

when a joint is injured, but a lesion confined only to articular cartilage is not painful. While
an animal is growing there is some remodelling of articular cartilage, but in adults, the

turnover and capacity for repair is limited.

SUBCHONDRAL BONE

Articular cartilage provides little shock absorption; this is provided by the underlying bone

and the soft tissues surrounding the joint. The subchondral bone immediately under the
articular cartilage is deformable when under pressure and so is able to support and protect the
articular cartilage.

THE JOINT CAPSULE

The joint capsule is composed of two layers.

• An outer fibrous layer which is attached to the periosteum of the bone. The collateral
ligaments are often incorporated into the joint capsule and together they provide stability
to the joint.

• An inner synovial membrane which lines the joint where there is no articular cartilage. It

secretes synovial fluid.

SYNOVIAL FLUID

Synovial fluid nourishes the articular cartilage and has a lubricating role within the joint. One

of the major components of synovial fluid is hyaluronan which gives the fluid its
characteristic viscosity.

OTHER PERIARTICULAR SOFT TISSUES

These include ligaments, tendons and muscles.
• Ligaments join together and stabilize the bones making up a joint.