Although epidemiological studies have promoted our understanding of the risk factors that predispose to OA, we do not yet understand the initiating events that trigger the disease. OA is primarily a disease of cartilage Cartilage is a unique tissue with viscoelastic and compressive properties which are imparted by its extracellular matrix, composed predominantly of type II collagen and proteoglycans (slide). Under normal conditions, this matrix is subjected to a dynamic remodeling process in which wrist arthritis arthritis in hands low levels of degradative and synthetic enzyme activities are balanced, such that the volume of cartilage is maintained. In OA cartilage, however, matrix degrading enzymes are overexpressed, shifting this balance in favor of net degradation, with resultant loss of collagen and proteoglycans from the matrix (slide). Presumably in response to this loss, chondrocytes initially proliferate and synthesize enhanced amounts of proteoglycan and collagen molecules. As the disease progresses, however, reparative attempts are outmatched by progressive cartilage degradation. Fibrillation, erosion arthritis in hands arthritis in hands and cracking initially appear in the superficial layer of cartilage and progress over time to deeper layers, resulting eventually in large clinically observable erosions. OA, in simplistic terms, therefore, can be thought of as a process of progressive cartilage matrix degradation to which an ineffectual attempt at repair is made. (top of page) Is OA simply a process of aging of cartilage? A critical question is whether OA is truly a disease or a natural chronic hip pain arthritis in hands consequence of aging. Several differences between aging cartilage and OA cartilage have been described, suggesting the former. For example, although denatured type II collagen is found in both normal aging and OA cartilage, it is more predominant in OA. In addition, OA and normal aging cartilage differ in the amount of water content and the in ratio of chondroitin-sulfate to keratin sulfate constituents. The expression of a chondroitin-sulfate epitope (epitope 846) in OA cartilage, that is otherwise only present arthritis in cats arthritis in hands in fetal and neonatal
