Introduction to the chronic arthritides

Abstract

Joints which possess a synovial-lined cavity are called diarthrodial joints. They comprise a variety of types of cells and structures. The articular surfaces of bones are covered by cartilage and lined by synovium which is normally approximately three cells thick. Some synovial cells secrete synovial fluid into the joint cavity, others are phagocytic. The subsynovium is formed from a matrix of collagen, proteoglycans and elastin; these molecules, secreted by fibroblasts, provide synovium with its strength and flexibility. The tissue contains also blood vessels, adipose cells, nerves and lymphatics. Cells from the circulation pass through synovium, thus a few leucocytes can be seen in the connective tissue of normal joints. Tendons or ligaments may insert into bones near joint margins at a site called the enthesis.