Mitzi Christopherson, age 16, of Montgomery, Ala., for her question:
WHAT IS SYNOVIAL FLUID?
Synovial fluid is also called joint fluid. It is a viscous, light yellow liquid secreted by the membranes that line the joints where two bones meet. The fluid facilitates joint motion, lubricates and aids in exchange of nutrients the tissues need.
Normal synovial fluid consists of extremely large, heavy molecules and is highly viscous or thick and sticky. When the joint is diseased, the fluid may increase in quantity, become inflamed and contain abnormal elements such as white cells, crystals, strands of callagen and bacteria. Analysis of the fluid may help a doctor to identify the condition.
Actually, joints may be fixed or movable. Fixed joints can be found in the cranium which is the skull and protective covering of the brain.
There are three main kinds of movable joints: hinge joints, pivot joints and bail and socket joints. Synovial fluid can be found in each of these joints.
Hinge joints are those which permit a forward and backward motion in one plane, like the motion of a door on its hinges. The joints at the knee and fingers are hinge joints.
Pivot joints give a rotating motion, such as the movement of the head from side to side. The elbow has both hinge and pivot joints.
Ball and socket joints allow the greatest freedom of movement. These joints are made up of a large round end of a long bone that fits into the hollow of another bone. The hip and shoulder have ball and socket joints.
The arms can move more freely than the legs because of the way the joints are arranged and because the shoulder blade is only loosely attached to the vertebral column by muscles and thin ligaments.
Movable joints are protected from wear and tear not only by the synovial fluid but also by a smooth layer of cartilage or gristle which covers the ends of bones that move over one another.
Bones are held together at the joint by strong ligaments that attach above and below the joint. At the hip, a number of ligaments circle the bone like a color to keep the joint in place.
Joints are often sprained or dislocated. A sprain occurs when the ligaments around a joint are torn or badly stretched. Serious sprains are painful and if neglected they may result in stiffening of the joint.
Dislocated joints should be treated as soon as possible by a doctor.
Inflammation of the joints may result from infections or from disturbances such as arthritis.
Body joints move billions of times in a lifetime and, although these joints can deteriorate as a result of wear and tear, most of them hold up well considering the use and abuse they take.