Immovable joints, like those connecting the cranial bones, have edges that tightly interlock. The outer surface of the synovial joints contains ligaments that strengthen joints and hold bones in position. Bursae are small sacs filled with synovial fluid that reduce friction in the joint. The knee joint contains 13 bursae Images from W.H. Freeman and Sinauer Associates, used by permission. Skeletal Disorders Injury, degenerative wear and tear, and inflammatory disorders affect joints.
Sprains are common injuries that cause ligaments to rip of separate from the bone.
Osteoarthritis is a degenerative condition associated with the wearing away of the protective caps of cartilage covering the bone-ends. Bony growths or spurs develop as the cartilage degenerates, causing restriction of movement and pain. Rheumatoid arthritis is a severely damaging arthritis that begins with inflammation and thickening of the synovial membrane followed by bone degeneration and disfigurement. More women than men are affected. There may be a genetic predisposition to rheumatoid arthritis.