An immovable joint is a place in the body where two bones are joined together but where little or no movement is normally possible and where no joint cavity exists, as is present in the majority of joints in the body in order to allow for a range of movement. There are several examples of these joints in the human body, including joints between the bones of the skull, joints in the pelvis and joints between the teeth and the mandible, or lower jaw, and the maxilla, or upper jaw. Another name for an immovable joins is a synarthrosis, which simply means immovable. The two types of immovable joints are fibrous joints and cartilaginous joints.
Among fibrous joints, there are two types that are considered to be an immovable joint: a suture joint and a gomphoses joint. In a suture joint, the edges of the joined bones fit tightly together much like pieces of a puzzle. Suture joints can be found between the various types of skull bones, which fit together along an uneven edge and are held in place by a special kind of fibers called Sharpey's fibers. A very small amount of movement is possible between the bones joined through suture joints, which is important because the slight flexibility in the suture joints in the skull helps protect the brain.
By contrast, in a gomphoses joint, one bone fits into the adjoining bone, and the two are held together with connective tissue. Gomphoses joints within the human body are found where the teeth are joined to the sockets in the jawbones. Although teeth technically are not bone, these still are considered to be fibrous joints. Again, a minimal amount of movement is possible, as evidenced by the ability to gradually change the position of teeth through the use of orthodontic braces.
A cartilaginous immovable joint, in which bones are joined together with cartilage, allows for greater movement than a fibrous immovable joint. Examples of cartilaginous joints include the joint that connects the upper portion of the sternum, or breast bone, to the lower portion; and a joint called the pubic symphysis, which joins the left and right halves of the pubic bone in the front portion of the pelvis. Other cartilaginous immovable joints are the juncture between the tibia and fibia in the forearm and joints in the ribs. These also are referred to as amphiarthrosis joins, or slightly movable joints.
