The point of connection between two or more bones is known as a joint. There are many types of joints in the body, and they can be classified in various ways. Two major ways joints are classified are by the amount of movement they allow and by the way they are formed. When classified by the amount of movement they allow, joints are either synarthroses, amphiarthroses or diarthroses. When classified by the way they are formed, joints are either fibrous, cartilaginous or synovial.
Synarthroses
Synarthroses are joints with essentially no movement. When bones are interlocked or joined together without any gap between their surfaces, they cannot move relative to each other to any substantial degree. Although synarthrotic joints can flex under extreme stresses, their strong connection enables them to act essentially as single bones to support and protect the body. Typical examples of these joints are the connections between the bones of the skull and those of the pelvic girdle.
Amphiarthroses
Amphiarthroses are slightly movable joints such as those found between the ribs and sternum or between vertebrae and ribs. These joints allow slightly more movement but still provide substantial stability and protection for more delicate parts of the body.
Diarthroses
Most joints of the body are diarthrotic, allowing free movement in one or more directions. These joints are the ones we would normally think of when we think of joints; common examples are the jaw, elbow, fingers, hips, ankles and toes. Diarthroses are further subdivided according to how they articulate or how the individual bones are joined.
Fibrous
Fibrous joints are joints in which the ends of the bones are tightly connected by fibrous tissues. These joints tend to be synarthrotic joints and allow very little movement. Examples include the sutures of the skull and the vertebrae.
Cartilaginous
Cartilaginous joints are joints in which the bones are attached by cartilage; they normally allow for limited movement and provide stronger support than most movable joints. Examples of cartilaginous joints are the pubic symphysis and the joints between the ribs and sternum.
Synovial
Synovial joints are by far the most numerous joints of the body. The synovial joints are characterized by the presence of synovial fluid within a space that encapsulates the articulating surfaces (surfaces that touch each other) of the joint. The synovial capsule reduces friction between the bones, allowing for smooth movement. There are six types of synovial joints: gliding, condoloid, saddle, hinge, ball and socket and pivot.
References
- "Gray's Anatomy: The Anatomical Basis of Clinical Practice;" S. Standring, Ed.; 2008
- "Trail Guide to the Body: How to Locate Muscles, Bones and More;" A. Biel; 2005
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