Joints

The points where bones meet — also called articulations. They determine how, and how much, the skeleton can move.

Classified by movement

• Immovable joints — e.g. the sutures of the skull.
• Slightly movable joints — e.g. between the vertebrae.
• Freely movable (synovial) joints — most joints of the limbs; a fluid-filled capsule allows a wide range of motion.

Synovial joint types

Hinge (elbow), ball-and-socket (hip, shoulder), pivot, gliding, saddle, and condyloid — each permitting a characteristic range of movement.

Key idea

Joints embody a trade-off between mobility and stability: the freely moving shoulder is also the joint most easily dislocated.