Joints

This page is about the joints in the skeleton that allow movement.

Basic structure

If two bones just moved against each other, they would eventually wear away. This can happen in people who have a disease called arthritis. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by synovial fluid. Tough ligaments join the two bones in the joint and stop it falling apart.

The diagram shows the main features of a joint.

A Joint

Movement

Different types of joint allow different types of movement.

• Hinge joints allow simple movement, the same as a door opening and closing. Knee and elbow joints are hinge joints.
• Ball and socket joints allow movement in more directions. Hip and shoulder joints are ball and socket joints.

The bones cannot move on their own - they need muscles for this to happen.