Joints are points in the human body where two bones come together. There are three major types of joints in the body, each serving a different function. Fibrous joints are largely immovable to provide stability; cartilaginous joints are slightly immovable to allow for stability with a little bit of give and shock absorption; and synovial joints are totally movable to allow for movement in one, two or three planes.
Fibrous Joints
Fibrous or immovable joints (synarthroses), are joints that are held together by a thin, strong layer of cartilage or connective tissue. There are three types of fibrous joints---suture joints, gomphoses and syndesmoses.
Suture joints are found only in the skull and are unique in that, while classified as immovable, they allow for skull growth. At birth, the cranial bones overlap to permit passage through the pelvis and birth canal. After birth, the suture joint becomes serrated to discourage excessive movement. The joint does not completely fuse until later in life when brain growth is complete.
Gomphoses (peg and socket joints) are immovable joints found between the teeth and jaws. They are held together by a periodontal ligament that acts as a shock absorber.
The syndesmosis joint is found at the intersection of the tibia (shin bone) and fibula (calf bone). A tight ligament holds the two bones together to limit movement.
Cartilaginous Joints
Cartilaginous joints are a slightly moveable type of joint found in the body. There are two types of cartilaginous joints---symphyses and synchondroses.
Symphysis joints are designed to allow for some give or motion, and they are held together by fibrocartilage (a mixture of fibrous connective tissue and cartilage). According to the Encyclopedia of Nursing and Allied Health (ENAH), one type of symphysis joint can be found in the vertebral column where one vertebra is attached to another by an invertebral disk, or cartilaginous ring. The ring allows for small movements between vertebrae as the spinal column flexes and extends. As described by the University of Leeds, a special example is the pubis (pelvic bones) which is held together by ligaments and fibrous cartilage. While normally closed, hormonal changes cause the bones to open during childbirth.
Synchondroses are joints that are held close together by hyaline cartilage (a strong, flexible shock-absorbing cartilage). Examples include the joint between the first rib and the upper part of the breast bone, and joints of the body where two long bones are separated by a cartilaginous plate. These plates permit bone growth throughout early development and later ossify so that, by adulthood, the joint is gone.
Synovial Joints
Synovial joints are considered movable joints, or diarthroses. According to the ENAH, they can be classified into uniaxial, biaxial and triaxial categories.
Uniaxial joints are those that hinge (such as the joints in the fingers) or pivot (such as the atlas and axis bones in the cervical vertebrae which allow the rotation of the head).
Biaxial joints allow motion on two planes and include saddle joints that allow rotation, such as the carpometacarpal (thumb) joint, and condyloid joints that allow two-way movement but no rotation, such as the metacarpophalangeal joints of the fingers.
Triaxial joints allow for movement in three planes and include ball and socket joints (like the hip) and plane joints that allow for gliding movements (such as carpal bones in the hands).
Member Comments