Joints

📖 In short

A joint is where two or more bones meet. Thanks to joints you can bend your knee, move your arm, turn your head and write with your fingers. Some joints never move, like those between the skull bones.

🤩 Did you know?

There are three kinds of movable joints: hinge, pivot and ball-and-socket.
The sound you hear when you crack your knuckles comes from bubbles in the joint fluid.
A doctor should treat a sprained joint quickly.
Strong ligaments tie the bones together in a joint so they don't come apart.

🔎 Find out more

🌟 A joint like a door

The knee and elbow joints are like a door hinge, moving only forwards and backwards. That's why you can bend your knee but can't twist it sideways.

🔍 The ball joint

The shoulder and hip have a ball-and-socket joint: the end of the bone is round like a ball and fits into a cup-shaped hollow, so the arm can move in every direction and turn.

💡 A joint that turns

Your neck has a joint that turns like a pivot, letting you turn your head left and right to say “no”.

🎯 A soft cushion

At the ends of the bones in a joint is a smooth layer called cartilage, with a slippery, oil-like liquid between them, so the bones move easily without rubbing against each other.

🧩 Test yourself

1 Which joint is like a door hinge?

2 What is the smooth layer on the ends of bones in a joint?

3 Which picture shows “Joints”?