For example, a bone of the lower leg, called the shin or tibia and the thighbone, called the femur, meet to form the knee joint. The hip is a ball and socket joint. The bone ends of a joint are covered with a smooth material called cartilage. The cartilage cushions the bone and allows the joint to move easily without pain. The joint is enclosed by a fibrous envelope called the synovium which produces a fluid that helps to reduce friction and wear in a joint.
Ligaments connect the bones and keep the joint stable.
Muscles and tendons power the joint and enable it to move. Inflammation is one of the body's normal reactions to injury or disease. In an injured or diseased joint, this results in swelling, pain, and stiffness. Inflammation is usually temporary, but in arthritic joints, it may cause long-lasting or permanent disability. Lose one pound, Smoking costs.