What are Joints?

Whether at work or at play, man almost always moves some part of his body. Arms, hands, legs and feet may be in motion. All of these movements are possible because most of the bones of the body are movable. They are connected to one another in some way. The points of connection between the bones are called joints.

There are certain bones of human bodies which have little or no need for movement. For example, the bones of the skull are fixed and immovable. They are joined so closely by fibrous tissues that the connections be­tween them appear only as lines. Such joints are called synarthroses. There are other bone junctions which provide for limited movement (amphiarthroses). An example of these connections is the socalled pubic symphysis. The pubic bones are in the lower front part of the abdomen near the genital region. These two bones are held together by bundles of thick fibers called ligaments. During pregnancy there is a relaxation of these connections in the female body which serves as a preparation for childbirth.

Those joints which move most freely (diarthroses] are usually classified as hinge, pivot, or ball-and-socket joints. The hinge joints allow backward and forward motion in one plane. The bending of the elbow, the knee and the fingers are examples of mo­tion provided by hinge joints.

The pivot joints allow for a rotating type of motion. For example the forearm can be moved in such a way that it seems to twist around itself. The head also moves in a rotating motion.

The connection between the thigh and the hip and between the shoulder and the arm provide good examples of the ball-and-socket joints. In such cases the head of one bone which is ball-shaped fits into a cavity of the other bone. Joints of this type provide the greatest freedom of movement. Usually the freely-moveable joints are held together by a capsule. The outer "region is made of thick fibrous material and the inner part is lined by some special tissue called synovial membrane which secretes a thick, sticky fluid called synovial fluid. This fluid provides lubrication for the joints.

There are some joints that do not move. The fused joints of the skull are not connected at birth but gradually grow toguether, or fuse, as the child grows.


The joints may be classified anatomically into the next groups:

1. Articulations of hand
2. Articulations of foot
3. Axillary articulations
4. Elbow joints
5. Wrist joints
6. Vertebral articulations
7. Sternoclavicular joints
8. Hip joints
9. Knee joints
10. Temporomandibular joints
11. Sacroiliac joints

A joint disorder is termed an arthropathy, and when involving inflammation of one or more joints the disorder is named an arthritis. Most joint disorders involve arthritis, but joint damage by external physical trauma is typically not termed arthritis.