Cartilage, tendons and ligaments connect the bones of the human body. The body's joints are classified by the material connecting the bones together and by functionalities or the things the joints are able to do. Joints found in the human body can be classified three ways: synarthroses (joints that do not move at all), amphiarthroses (joints that are slightly movable) and diarthroses (freely movable joints). The freely movable joints, the most common joints found in the full-grown human body, are grouped into six categories.
Ball and Socket
Ball and socket joints, sometimes referred to as the "enarthrosis" or "spheroidal" joints, allow for a wide range of rotating movements–the greatest of all joints. A spherical head of a bone fits into a socket-like bone, much like the way the eyeball fits into its socket. Examples of these joints can be found in the bones of the shoulders and hips.
Condyloid joints are similar to ball and socket joints: the head of one bone fits into the socket of another. The major differentiating feature between the ways these two joints work is the joint shape. Condyloid joints are not as spherical as ball and socket joints–condyloids are oval shaped. Examples of these are found in the fingers, toes and wrist.
Hinge joints are similar to a door on a hinge; these joints allow flexion and extension of the joint. These joints also allow for some slight rotation. Examples are found in the ankle, knuckle (finger), and in the largest hinge joint in the human body, the knee.
Saddle joints are joints where one bone moves, or glides, in two directions. When comparing these to the other five joints, the range of motion is most similar to the condyloid. An example of a saddle joint is in the thumb’s base.
In gliding joints, which are often called a "plane joint," one bone moves (or glides) over or along another. As "plane" implies, these joints are able to move in all direction of a plane and the joint capsule limits movement of the joint. Examples are seen in the wrist and ankle.
The bones of a pivot joint move by rotating or "pivoting" around another bone. One of the bones is ring-shaped and the other, pivot-like. A commonly cited example is at the base of the skull. This joint enables the head to move from one side to the other.