By: Doron Ilan, MD
Between 25-50% of people will crack their knuckles at some point. In some of these people it becomes habitual. Parents across the world have been telling their kids (and spouses) “Don’t crack your knuckles. You are going to get arthritis!” Is this true? What is actually happening when someone cracks their knuckles?
What happens when you crack your knuckles?
Our knuckle joints (metacarpo-phalangeal joints) are synovial joints. Meaning there are two cartilage covered bones that meet each other and are surrounded by a joint capsule which contains synovial fluid (lubricant). When our joints move normally the synovial fluid lubricates the ultra-smooth cartilage and the bones glide silently over each other. When someone pops their knuckle, the pressure exerted on the joint and synovial fluid forces dissolved gases out of the synovial fluid. This creates what is called a cavitation bubble. This forms very quickly and explosively. This cavitation bubble then pops. It is believed that the sound of knuckle cracking is due to the formation or popping of the cavitation bubble. This would be similar to either the opening of a champagne bottle (sound caused by formation of the bubbles) or popping bubble wrap (sound caused by popping the bubble). To this day, we are still not 100% sure which one it is. The thing we are sure about is that knuckle popping is not due to bone rubbing on bone or tendons popping.
Are all sounds coming from a joint due to gases?
No. In arthritis (loss of cartilage) you can get a crunching sound called crepitus as bone rubs on bone. Some people have loose joints and the joint can sublux or partially dislocate. A tendon can shift over a moving joint and cause a pop or clunk. A torn labrum (hip or shoulder) or meniscus (knee) can also cause popping in a joint. Note: If you have pain associated with any noise from a joint you should consult your doctor.
Is knuckle cracking bad for you? Does it cause arthritis?
This may come as a shocker to parents everywhere but there is no evidence that knuckle cracking is bad for you or causes arthritis. It is certainly annoying and there have been case reports where people tried to crack their knuckles with such force that they caused a sprain or fracture, but despite multiple studies it appears that routine knuckle cracking is safe. There was even one doctor (Donald Unger) who decided to do a study on himself. He cracked the knuckles on one of his hands for 50 years while not cracking the other. He found no difference between the two hands in the end.
So go ahead and crack your knuckles. Just don’t do it around me.
For more from the experts at Northeast Orthopedics and Sports Medicine, feel free to contact us for a consultation.