Synovial Fluid

Synovial fluid status is difficult to measure clinically, so symptoms, range of motion, and treatment response are used as practical markers. Gas dissolved in synovial fluid is released when the joint is stretched, producing the popping sound. Synovial fluid is a lubricating liquid that surrounds finger joints and reduces friction during movement. Synovial fluid reduces friction between articular cartilage surfaces during movement. Cartilage depends on movement-driven compression and release because it has no direct blood supply. Aging and osteoarthritis reduce synovial fluid quality by lowering hyaluronic acid concentration and molecular weight. Morning stiffness is explained partly as a synovial fluid distribution and lubrication problem after immobility. The synovial membrane helps maintain the fluid between joint surfaces. Increased synovial membrane permeability may allow molecules that thicken synovial fluid to leave the joint space. Synovial fluid changes are proposed as one possible explanation for why some arthritic joints are painful and others are not. Thinner synovial fluid may reduce lubrication and contribute to joint-space narrowing or bony contact in severe cases.