Why Do Joints "Crack", and Is It Safe?

Pop, click, crack. Many people's joints make noises, especially knees on stairs, knuckles, necks and backs. It's often worrying. Is it arthritis? Is something damaged?

In most cases, joint noises are normal and harmless.

What causes the sound

1. Gas bubbles in the joint fluid Joints are surrounded by fluid that contains dissolved gases. When a joint is stretched, for example when cracking your knuckles, pressure changes can cause a gas bubble to form, making a pop. That's why you can't usually crack the same knuckle again straight away.

2. Tendons and ligaments moving Tendons can snap slightly over bony bumps as you move, causing a click. This is common around the hip, knee, ankle and shoulder.

3. Rough joint surfaces In arthritis, joint surfaces can become less smooth. This sometimes produces a grinding or crunching feeling, called crepitus.

Does cracking your knuckles cause arthritis?

The evidence so far suggests that habitual knuckle cracking does not cause arthritis. Studies comparing people who crack their knuckles with those who don't have not found a clear link.

When noises are nothing to worry about

• No pain
• No swelling
• The joint moves normally
• It's been happening for a long time without change

When to get it checked

• Noise with pain, especially after an injury
• Swelling
• The joint locking (getting stuck) or giving way
• Reduced movement
• A new noise after an injury, especially with a pop at the time of injury

These can be signs of a problem such as a meniscus tear, ligament injury or arthritis that may benefit from treatment.

Self-cracking the neck or back

Many people feel the urge to crack their neck or back for relief. Occasionally, it's unlikely to be harmful. But if you feel you need to do it constantly, the area may be stiff or overworked, and targeted exercises can help. Avoid forceful twisting of the neck.

Manipulation by a professional

Physiotherapists sometimes use manipulation, a quick, controlled movement that may produce a pop. The sound itself isn't what makes it work. It's done only after an assessment and with your consent.