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).