What are joints?

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, Temporomandibular joint disorder, and joint dislocation. Osteoarthritis is the most common joint disorder and occurs when the joints become swollen and more difficult to move. Temporomandibular joint disorder refers to a joint condition that affects the jaw, and may be caused by a number of factors (such as chewing, trauma to the jaw, etc). A joint dislocation is characterized by two bones separating from their meeting point. It may caused by a fall, sudden impact or other form of trauma.


What are synovial joints?

Synovial joints, also known as movable joints, refer to the joints that are capable of moving in a variety of directions (allow mobility). Synovial fluid fills the joints to make them move more easily. Such examples include the knee joints, elbow joints, wrist joints, shoulder joints, hip joints and ankle joints.


What are semi-mobile joints?

Semi-mobile joints, also known as amphiarthrosis joints, refer to the joints that are characterized by limited movement. Such examples include the spine.


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. They are called “fixed” or immovable” because they do not move.


What function do 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.

The main function of the movable joints is to allow the execution of a wide range of movements, as in the case of the knee joint or the elbow joint. The types of synovial joints are based on the shapes and can be classified in various forms: plane, hinge, pivot, condyloid, saddle, and ball and socket. The semi-mobile joints allow certain movements to be made, as well as act as supporting structures. Finally, fixed joints permit stability to certain areas of the body (ex: skull and pelvis), although they do not move.