How are joints classified ?
Joints are classified in two ways: structure (how the bones are connected) and function (how many degrees of freedom the joint has).
There is a third category of joints called biomechnical joints that include all surgical implants that replace damaged organic tissue (surgical knee, shoulder, and hip joints for instance).
Within the structure classification you have fibrous joints (like skull sutures), which are connected by fibrous connected tissue, cartilaginous joins (like vertebrae), which are connected by cartilage, and synovial joins (like the shoulder, hip, elbow, knee, etc.), which are not directly connected at all.
Within the functional classification you have synarthrosis (little or no mobility, usually fibrous joints), amphiarthrosis (slight mobility, usually cartilaginous joints), and diarthrosis (lots of movement, usually synovial joints).
Joints or articulations are classified by the degree of movement they allow and how they communicate with each other. Synarthroses means no movement, a synarthrotic joint does not move at all. Fibrous connective tissue grows between the articulations. A good example of this type of joint are the cranial sutures, when the bones of the cranium eventually fuse together in the infant.
Amphiarthroses means slight movement, an amphiarthrotic joint has cartilage between the articulations which allows for very slight movement. Examples of this type of joint are the pubic bones, the symphysis pubis.
Diarthroses means freely movable and diarthrotic joints allow for considerable movement. The knee and elbow are good examples of this type.
Joints can be separated into two classes: functional and structural.
Joints are divided into three different functional classes. They are synarthroses, amphiarthroses, and diarthroses. Synarthroses means the joint is immovable, amphiarthroses means the joint is slightly moveable, and diarthroses means the joint is freely moveable.
Joints can also be classified by structure. They are fibrous, cartilaginous, and synovial. When the joint is fibrous it means it is connected by fibrous connective tissue. When the joint is cartilaginous it means it is connected by cartilage. When there is a synovial joint it means that the joint is not connected at all.
Joints between bones can be classified based on how the bones connect with each other. There are three categories here:
- fibrous joint- here the bones are joined tgether by a fibrous connective tissue
- cartilaginous joint- here they are joined by cartilage
- synovial joint- in this case the bones are not joined directly
Joints can also be classified based on the degree of movement allowed between the joining bones:
- synarthrosis joint do not permit any mobility
- amphiarthrosis joints permit slight mobility
- diarthrosis joints allow movement in various directions