Joints

The point at which two or more bones meet is called a joint, or articulation. Joints are responsible for movement, such as the movement of limbs, and stability, such as the stability found in the bones of the skull.

Classification of Joints on the Basis of Structure

There are two ways to classify joints: on the basis of their structure or on the basis of their function. The structural classification divides joints into  fibrous, cartilaginous, and synovial joints depending on the material composing the joint and the presence or absence of a cavity in the joint.

Fibrous Joints

The bones of fibrous joints are held together by fibrous connective tissue. There is no cavity, or space, present between the bones and so most fibrous joints do not move at all, or are only capable of minor movements.  An example of a fibrous joint is a suture which is found only in the skull and possess short fibers of connective tissue that hold the skull bones tightly in place (Figure 38.23 Links to an external site.).

Figure 38.23 Sutures are fibrous joints found only in the skull.

Cartilaginous Joints

Cartilaginous joints are joints in which the bones are connected by cartilage. Cartilaginous joints are found in the epiphyseal plates of growing bones in children.  Cartilaginous joints allow for very little movement.

Synovial Joints

Synovial joints are the only joints that have a space between the adjoining bones (Figure 38.25 Links to an external site.). This space is referred to as the synovial (or joint) cavity and is filled with synovial fluid. Synovial fluid lubricates the joint, reducing friction between the bones and allowing for greater movement.  Synovial joints are capable of the greatest movement of the three structural joint types; however, the more mobile a joint, the weaker the joint. Knees, elbows, and shoulders are examples of synovial joints.

Figure 38.25 Synovial joints are the only joints that have a space or “synovial cavity” in the joint.