In anatomy, the term "articulation" refers to an arrangement of structures that keeps two or more contiguous bony surfaces together. Thus, articulation represents a set of elements (fibrous tissue and/or cartilage, ligaments, capsules, membranes) that regulate the connection between two skeletal segments.
A joint is a point in the body where bones meet. They make movement possible by making the skeleton flexible. The main bones that form the joints include the following:
- Synovial joints: knee, wrist, shoulder, elbow, ankle, and hip joints
- Semi-mobile joints: articulation of the spine
- Fixed joints: joints of the bones of the skull or pelvis
Joints are classified by how much movement they allow (function) or what they are made of (structure). Most allow free movement, some only allow movement in certain ways and others allow no movement. By use of scientific terminology, we speak respectively of synovial joints, synarthrosis joints and amphiarthrosis joints.
In regards to joint disorders, the three most common types include: osteoarthritis, arthritis, and traumatic injuries. Osteoarthritis is the most common joint disorder and occurs when the joints become swollen and more difficult to move. Arthritis refers to a joint condition that causes inflammation of one or more joints. Traumatic injuries are characterized by two bones separating from their meeting point. They may caused by a fall, sudden impact or other form of trauma. Other disorders may involve cancers and birth defects (such as hip dislocation). Seeking treatment is essential in any of these cases in order to help relieve symptoms as well as prevent any complications from arising.
What are fixed joints?
Fixed joints, also called synarthrosis joints, refer to the joints that provide stability to certain areas of the body, such as the joints of the bones of the skull and pelvis. They are characterized by the continuity of bony segments that are tightly joined and are separated by a thin layer of fibrous connective tissue. Synarthrosis joints are called “fixed” or immovable” because they do not move.
There are three different types of fixed joints in the body: sutures, syndesmoses and gomphoses. Sutures are the junctions between the skull bones. They include:
- Plane suture: The edges of the articulating bones are fairly smooth
- Serrate suture: The most common suture, includes sharp interlocking articulations
- Lap suture: The edge of one bone overlaps another articulating bone
Syndesmoses are fixed joints between two long bones. An example of a syndesmosis is the joint of the tibia and fibula in the ankle. Movement in these types is determined by the length of the connective tissue fibers. Finally, gomphoses refer to joints between the tooth roots and the mandible or maxillary bones.
What function do fixed joints serve?
The main function of the joints is to allow both movement and flexibility. They tend to be classified by the degree of their possible movement, the number of bones involved and the complexity of the joint.
Fixed joints permit stability to certain areas of the body, although they do not move. Examples of fixed joints include the joints between the bones in the skull and the joint where the radius and ulna bones meet in the lower arm.
