Articular cartilage

Articular Cartilage is a type of connective tissue that covers the surfaces of bones in synovial joints. It is composed of chondrocytes, which are cells that produce a large amount of extracellular matrix composed of collagen fibers, proteoglycan, and elastin fibers.

Structure

Articular cartilage is divided into four zones: the superficial zone, the middle zone, the deep zone, and the calcified zone. Each zone has unique structural and functional characteristics that contribute to the overall function of the joint.

Superficial Zone

The superficial zone, also known as the tangential zone, is the thinnest layer and the first line of defense against the wear and tear of the joint. It contains the highest concentration of collagen fibers, which are oriented parallel to the joint surface.

Middle Zone

The middle zone, or transitional zone, contains randomly oriented collagen fibers and has a higher concentration of proteoglycan than the superficial zone. This zone is responsible for distributing forces applied to the joint.

Deep Zone

The deep zone, or radial zone, contains collagen fibers that are oriented perpendicular to the joint surface. This zone has the highest concentration of chondrocytes and is responsible for the bulk of the cartilage's tensile strength and resistance to compression.

Calcified Zone

The calcified zone separates the cartilage from the underlying bone and anchors the cartilage to the bone. The boundary between the calcified zone and the deep zone is known as the tidemark.

Function

Articular cartilage serves several functions in the body. It reduces friction in the joint during movement, absorbs shock, and distributes load across the joint. The smooth, slippery surface of the cartilage allows for easy movement of the joint, while the elastic properties of the cartilage allow it to deform under load and then return to its original shape when the load is removed.

Pathology

Damage to the articular cartilage can lead to osteoarthritis, a degenerative joint disease characterized by the breakdown and eventual loss of the cartilage of one or more joints. Osteoarthritis is the most common form of arthritis, affecting millions of people worldwide.

See Also

• Synovial joint
• Chondrocyte
• Collagen
• Proteoglycan
• Osteoarthritis