Ball and socket joints are the most mobile and intricate of all the joints. They are also the most prone to disease and prone to require medical intervention. Arthritis is one of the conditions that causes pain and dysfunction in the ball and socket joint.

The role of pivot joints in human health (the same as that played by the other types of synovial joints) is to allow freedom of movement and thus provide flexibility to the skeleton.

A gliding joint allows three different kinds of motion: linear motion, such as smooth sliding of bone past bone, angular motion such as bending and stretching, and circular motion. The ends of the bones that a gliding joint joins are nearly flat or only slightly curved and thus facilitate the characteristic sliding, bending, and twisting movements.

Flexion and extension are opposite movements, but they’re easy to visualize. When you bend your elbow, you decrease the angle between your upper arm and your forearm. This is an example of flexion. When you straighten your arm, you’re extending it, increasing the angle between your upper and lower arms. This is an example of extension.

Abduction and adduction are movements related to the midline of a structure. For example, spreading your fingers wide moves them away from the midline down the center of your hand. Adduction is a return toward the midline.

Some saddle joints are also capable of combining flexion-extension and abduction-adduction movements.