Is it safe to crack your knees and knuckles? This is a question that gets asked a lot. Paul Hsieh, MD answers in his latest Forbes column.
As a radiologist specializing in orthopedic and joint disease, I get asked that question regularly — including by friends and family members trying to get a “professional” to tell another family member that it’s “bad for their joints” (or that it’s “totally fine”).
Thus, I was interested in recent communication by Dr. Harshvardhan Singh of the University of Alabama indicating that painless cracking of the knee joint is usually not a problem. In particular, Singh notes it is quite normal for knees to crack during activities such as running, walking and squats. He advises patients, “If you have no pain during these activities, then you should not be worried about the cracking sound during the performance of these movements.”
Nor does the sound of cracking imply that there is arthritis within the joint.
However, Singh stated that if the patient does experience pain with cracking, then he or she should see a physician or other health professional. Similarly, if the joint didn’t crack previously, but started cracking after an injury, then the patient should seek professional attention even if there is no associated pain. In these circumstances, the cracking may indicate some internal joint damage.
Similarly, cracking one’s knuckles is almost certainly harmless. In 1998, Dr. Donald Unger summarized the results of 50 years (!) of self-experimentation in which he cracked the knuckles of his left hand at least twice a day, but diligently did not crack the knuckles of his right hand. This was in response to repeated advice from “his mother, several aunts, and, later, his mother-in-law” that his knuckle cracking would lead to arthritis.
After 50 years, Dr. Unger summarized his results in a letter to the journal Arthritis and Rheumatism. He reported he cracked his left hand knuckles at least 36,500 times, whereas the right only cracked “rarely and spontaneously.” After 50 years, “There was no arthritis in either hand, and no apparent differences between the two hands.”
Unger also noted, “This result calls into question whether other parental beliefs, e.g., the importance of eating spinach, are also flawed. Further investigation is likely warranted.”
This man is my hero. (And he won an Ig Nobel prize for his work.)
A more formal study published in 2017 in Clinical Orthopaedics and Related Research showed similar results in a group of 40 volunteers. Dr. Robert Boutin (a musculoskeletal radiologist) and colleagues found that habitual knuckle cracking was not associated with any measurable impairment in joint mobility or function.
Interestingly enough, the 2017 study also included high-resolution real time ultrasound of joints while they were cracking. The cracking noise appeared to be correlated with “tribonucleation” or the formation of tiny gas bubbles in the joint caused by sudden negative pressure created by stretching the joint capsule. (Click here for a video of the ultrasound images.)
Dr. Rachel Lefebvre, a hand surgeon at University of Southern California thus summarizes, “From what we have so far, it looks like there is no correlation between knuckle cracking and joint damage or arthritis.” (In line with Dr. Singh’s advice, the USC Keck School of Medicine website similarly advises that if patients feel pain while cracking their joints, they should see a doctor.)
Summary: If your knees or knuckles crack but they don’t otherwise hurt, then don’t worry about it — even if your grandmother told you otherwise. Whether or not you should eat spinach is a topic for another day.