A joint is described as the junction where two bones come together. It can involve cartilage as in the knee or simple articulation as in the case of the jaw where teeth fit into the bone. Most joints are movable and help us to play sports, exercise and function in day-to-day living.
Ligaments and fibrous connective tissue hold joints together. There are synovial joints that have cavities where the bones meet.
Joints are described by their movement; non-movable, slightly movable and freely movable.
Synarthrosis joints are non movable like the skull. Fibrous tissue holds the suture lines together. When the skull forms in utero, it fuses together before birth, forming the suture lines.
Syndemosis describes the joining of two bones with cord ligaments or sheets of fibrous tissue. An example is the tibia and fibula joint of the lower leg. The two bones are joined together before reaching the knee joint. Another example is the ulna and radius of the forearm.
Gomephosis is the name for the joint that describes where the teeth join the jaw. It is the periodontal ligament that holds the tooth in the socket.
Slightly Movable: Amphiarthrosis
There are 24 ribs in 12 pairs starting where the clavicle and breastbone meet and ending around the waist. The ribs form the thoracic cage. The ribs are attached to the breastbone with the exception of the lowermost pair. Joined by cartilage, the ribs are described as amphiarthroses because they permit slight movement.
Another example of cartilage and slight movement are the two pubic bones.
Cartilage in the spine allows for the slight movement of the vertebrae. A spongy material lies between each vertebral space.
Freely Movable: Diarthrosis
Free-moving joints are synovial, containing a fluid that keeps the joint moving smoothly. The joint cavity allows the movement of the bones, which are joined by cartilage attached to the periosteum coating the bone.
The hands, feet and knee cap have synovial joints. They are gliding joints that move side to side.
The fingers, toes, elbows and knees have hinge joints that are synovial and move in one plane.
The ball and socket joint of the hip is synovial and can pivot with full movement. The shoulder is similar in its ability to have full, "circular" range of motion.
Ellipsoidal joints found in the wrist allow free movement in the form of rotation, but do not allow pivoting.
Some people have very loose cartilage in these types of joints that allow them to move the joint beyond its normal range. The loose cartilage can cause injury to the joint and, in some cases, the bone.