A joint is a place where one bone meets another bone. Joints are a major part of the skeletal system. There are many joints, some of which allow no movement, some allow minor movement, and some allow free movement.
The immovable joints are called synarthroses, or fibrous joints. They are firm in their position to prevent gliding or sliding. There are three major groups of this joint. First there are sutures, like the joints between the bones of the skull. Next, there are syndesmoses, like the membrane that sketches in between tibia and fibula in human beings. Finally, there is gomphosis which are the joints between the teeth and sockets that hold them.
The next group of joints is the cartilaginous joints, or symphyses, which connect two bones with cartilage. Only slight movement occurs between the bones that have this joint connecting them. Two cartilaginous joints are synchondrosis, and fibrocartilaginous joints. The more common of these two joints is the synchondrosis. This joint is a layer of cartilage between two of part of two bones. Fibrocartilaginous joints are bound between the bones of the vertebral column. It is also between the sternum and its inferior.
The final group of joints is synovial joints, or diarthroses. These joints allow various movements depending on the type of joint. Cartilage covers bones near synovial joints so that ligament attachment can occur. Between tow bones in these joints there is a membranous sac called bursa. Bursae produce synovial fluid which covers the ends of bones allowing smooth movement. Bursitis, a condition where the bursa undergo inflammation, causes severe pain.
There are several typed of synovial joints. Plane joints are joints between two flat bones where one bone moves horizontally over the other bone in various directions. An example is the bones in a hand. Pivot joints occur between two bones where one bone is cylindrical in shape and rotates inside a ring shaped bone or ligament. An example is the movement that occurs between the first two bones of the vertebrae where someone shakes his head "no" (Johnson). The hinge joint is like the hinge on a door, and it moves back and forth in one plane. The elbow and knee joints are examples. Condyloid joints, also called ellipsoid joints, occur between two bones where one is football-shaped and fits in its concave complementary "partner." The movements occur when someone shakes his head "yes" (Johnson) or when he tilts his head side to side. The saddle joint is two saddle shaped joints that can move ninety degrees over each other like a jockey can tilt side to side on a horse, but he cannot tilt too far without falling off. The final joint is the ball and socket joint, which is like an adult hand loosely wrapping one hand around a baby's hand. Examples of this joint are the joints in the hips and shoulders.
