The Stainable Mucin of Joint Tissues and Synovial Fluid

Abstract

JOINT synovial fluid is considered to be a dialysate of blood with added mucin, which consists of hyaluronic acid¹. The source of the latter is uncertain, but the belief is current that the synovial membrane is the likely site of formation. Articular cartilage is said to contain no hyaluronic acid, and the sulphated mucopolysaccharide it does contain is not found in appreciable quantity in synovial fluid. Synovial membrane is not lined by an epithelium, but is composed of fine, compact connective tissue of variable cellularity², the cells being indistinguishable from fibroblasts by electron microscopy³. Claims have been made that the ‘membrane’, especially in its superficial part, stains with mucicarmine^4–6, and also reacts with the periodic acid – Schiff technique³. Metachromasia, which might indicate the presence of hyaluronic acid in the membrane, has not been unequivocally demonstrated; some claim that the membrane is metachromatic^6,7, but others deny it^3,5.