Aggrecans – An aggregating form of proteoglycan composed of many glycosaminoglycan chains bound to a protein core


Articular cartilage – The tissue that forms the opposing surfaces of synovial joints

Calcified zone – The fourth zone and deepest layer of articular cartilage; separates hyaline cartilage from the subchondral bone

Collagen – A triple helix protein that is the major structural macromolecule of the ECM of articular cartilage; found also in bone, tendon, and ligament

Deep zone – The third zone of articular cartilage in which the collagen fibers are organized vertical to the joint surface, and the chondrocytes are arranged in a columnar fashion

Extracellular matrix (ECM) – A complex structural entity surrounding and supporting cells that are found within tissues; the primary components of ECM in cartilage are water, proteoglycans, and collagens, with other proteins and glycoproteins present in smaller amounts

Glycosaminoglycans – Polysaccharides consisting of long-chain, unbranched, repeating disaccharide units, such as keratan sulfate and chondroitin sulfate

Middle (transitional) zone – The middle zone of articular cartilage in which collagen fibers are less organized and the chondrocytes have a more rounded appearance

Osteochondral fractures – Injuries that disrupt articular cartilage and the underlying subchondral bone

Proteoglycans – Complex macromolecules that consist of a protein core with covalently bound polysaccharide (glycosaminoglycan) chains

Superficial tangential zone – The smooth, nearly frictionless gliding surface of articular cartilage in which thin collagen fibrils are arranged parallel to the surface

Tidemark A – wavy bluish line visible on histologic staining with hematoxylin and eosin that signifies the border between the deep zone and the zone of calcified cartilage