As a person ages, the surface layers of cartilage at the joints which cushion them often loses its ability to support healthy cellular growth and eventually breaks down and wears away. In addition, the synovial fluid that lubricates the joints deteriorates. Synovial fluid reduces friction in the joints and acts as a shock absorber. This break-down allows bones under the cartilage to rub together and cause pain, swelling, and loss of motion of the joint.