Have you ever heard someone cracking their knuckles and wondered what’s causing the “popping” sound?  Hint: it has to do with your joint capsule, a fluid-filled connective tissue container that surrounds and contains your joint.  The fluid inside contains gases including oxygen, nitrogen and carbon dioxide.  When you stretch of pull your joint beyond its normal range of motion, the pressure inside the joint capsule changes, creating a vacuum effect and causing a gas bubble to form and burst with a “pop”!

Another, much less amusing and more serious cause of joint popping is because something (like a torn or loose piece of knee cartilage) is caught between the joint surfaces.  When this happens, sometimes the knee can lock with a loud ‘pop’. Once a joint is stuck like this, it may need to be jostled around to free the object that is stuck – and when it is dislodged it can cause another pop.  Ew.

What you probably REALLY wanted to know though – was whether your mom was right when she said you shouldn’t crack your knuckles.  And of course she was right!  She’s always right, isn’t she? Studies have shown that knuckle cracking is related to hand swelling, lower grip strength and damage to the ligaments that surround the joint.  And if you stop to think about it, when is it ever a good idea to forcefully tug your joints beyond their natural end range? *crickets*

You never actually NEED to crack your knuckles, but you might sometimes feel like stretching your hands and fingers.  Next time you get the urge to crack your knuckles, try this Yoga Tune Up® wrist stretch instead.

This article is part 4 of a 4-part series on interpreting sounds from the joint space. 

Enjoyed this article? Read Snap, Crackle and Pop – Part III: Crackle and Crepitus 



Nichols, Hannah.  “Why do knuckles and joints crack? Can cracking joints cause arthritis?” Medical News Today. February 3, 2015.

Everyday Mysteries.  Fun Science Facts from the Library of Congress.  “What causes the noise when you crack a joint?”  Retrieved from http://www.loc.gov/rr/scitech/mysteries/joint.html. February 3, 2015.

Matsen, Frederick A. III, MD. “Joints.” UW Medicine.  www.orthop.washington.edu

Comments (44)

Leave a Reply

Your email address will not be published. Required fields are marked *