Arthrosis: An arthrosis is a joint, an area where two bones are attached for the purpose of motion of body parts. An arthrosis (joint) is usually formed of fibrous connective tissue and cartilage.

Joints are grouped according to their motion: a ball and socket joint; a hinge joint; a condyloid joint (a joint that permits all forms of angular movement except axial rotation); a pivot joint; gliding joint; and a saddle joint.

Joints can move in four and only four ways:

• Gliding -- one bony surface glides on another without angular or rotatory movement;
• Angular -- occurs only between long bones, increasing or decreasing the angle between the bones;
• Circumduction -- occurs in joints composed of the head of a bone and an articular cavity, the long bone describing a series of circles, the whole forming a cone; and
• Rotation -- a bone moves about a central axis without moving from this axis.

The word "arthrosis" comes from a Greek root, "arthros" meaning a joint (as in arthritis, inflammation of a joint). The word "joint" itself comes from a Latin root, "junctio" meaning a joining (as in a junction).