Why do my joints crack? A physiotherapists guide to cavitation.

Written by Andreea Brown - Physiotherapist -

Hearing a crack, pop, or creak from your joints can be surprising or even a little concerning. But in many cases, this is a completely normal process known as joint cavitation.

Understanding your joints:

Joints are the connection points between bones, providing both stability and movement. While the body contains various types of joints, the most common and most mobile are synovial joints.

What are synovial joints?

Synovial joints are structures that include: two or more bones connecting (articulating), a joint capsule, ligaments, articular cartilage, blood vessels and sensory nerves which are lined by synovium and are contained within a synovial fluid filled sac.

These joints are found in many areas of the body including:

● Neck and back

● Shoulders

● Elbows

● Wrists and fingers

● Hips

● Knees

● Ankles and toes

So… why do synovial joints crack?

1. Joints are surrounded by synovial fluid, to lubricate the joint space and create smooth movement

2. When the joint is moved, the space within the joint briefly increases

3. This creates a sudden drop in pressure within the synovial fluid

4. As pressure drops, gases (mainly nitrogen) dissolved in the synovium form tiny little bubbles

5. The bubbles then have no space to move so they have to exit the joint → these bubbles collapse or ‘pop’ creating the cracking sound you hear!

Fun fact: After cavitation occurs, it typically takes 20 minutes for the gas bubbles to re-dissolve and reset - this is why you can't crack the same joint immediately again https://pmc.ncbi.nlm.nih.gov/articles/PMC4398549/

Is it normal?

Yes - joint sounds without pain are usually a normal physiological response, especially when bending, stretching, or moving after being still (like in the morning or sitting for long periods of time).

However, if you’re experiencing discomfort or are unsure whether your joint symptoms are normal, all Physiotherapists at Newcastle Aquatic Physiotherapy are here to help. We’re trained in detailed movement assessments and can guide you toward safe, effective treatment tailored to your needs.

And if you’re one of our long-term clients—feel free to ask us more about this fascinating topic at your next appointment. We love sharing the science behind how your body works! If you want to read more check out the following link on synovial joints: https://open.oregonstate.education/aandp/chapter/9-4-synovial-joints/