Cracking the Myth: What Really Happens When You Crack Your Knuckles

Cracking your knuckles is one of those habits that has been around for as long as we can remember — and so has the warning: “Don’t do that, you’ll get arthritis!” But is there really any truth to it?

From an osteopathic perspective, let’s break down what’s really happening inside your joints, why it makes that satisfying sound, and whether it causes harm.

The Anatomy & Physiology of Knuckle Cracking:

Our knuckles are synovial joints of the metacarpophalangeal (MCP) joints. These joints are enclosed by a joint capsule and filled with synovial fluid, which lubricates the joint and reduces friction between the articular cartilage surfaces (Standring, 2021, Gray’s Anatomy).

When you “crack” your knuckles:

• Joint distraction occurs — you stretch the joint capsule slightly, creating negative pressure inside.

• Gas bubbles form and collapse in the synovial fluid (mainly carbon dioxide and nitrogen). This process is known as cavitation.

• The audible “pop” is the sound of these gas bubbles rapidly forming or collapsing. (Kawchuk et al., 2015, PLOS ONE).

Importantly, this is a physiological response — not a sign of damage. After cracking, it usually takes around 20 minutes before you can do it again, as the gases re-dissolve into the synovial fluid.

Is It Harmful? What does the research really say?

The strongest myth around knuckle cracking is its supposed link to arthritis.

Multiple studies have investigated this:

• Donald Unger’s famous experiment: He cracked the knuckles of one hand for 60 years while leaving the other untouched. Result? No difference in arthritis between the two hands (Unger, 1998, Arthritis & Rheumatism).

• Lederer et al. (1990): A radiographic study of long-term knuckle crackers found no increased risk of osteoarthritis compared to non-crackers.

• Castellanos & Axelrod (1990): While knuckle cracking was not associated with arthritis, frequent crackers did show slightly higher rates of hand swelling and reduced grip strength — possibly due to repeated stretching of the joint capsule and ligaments.

So, the verdict? Knuckle cracking doesn’t cause arthritis. At worst, excessive and forceful cracking may contribute to soft tissue irritation, joint laxity, or minor hand swelling, though this is uncommon.

The Osteopathic Perspective:

From an osteopathic point of view, joint cavitation isn’t inherently negative. In fact, osteopaths and other manual therapists often use joint mobilisation and manipulation techniques that can create similar cavitation sounds.

The goal, however, is not the “crack” itself, but the therapeutic effect:

• Restoring joint motion

• Reducing muscle tension via neurological reflexes

• Improving local circulation and lymphatic flow

When patients self-crack, especially repetitively or aggressively, they may be targeting joints that are already mobile while leaving the stiffer, dysfunctional ones untreated. Over time, this could reinforce imbalance rather than resolve it. That’s why an osteopathic approach focuses on the whole body’s biomechanics, not just the sound of a joint release.

The Bottom Line:

• Knuckle cracking does not cause arthritis.

• The “pop” is simply gas bubbles forming and collapsing in synovial fluid.

• Excessive or forceful cracking may irritate soft tissues, but for most people it’s harmless.

• If you feel constant stiffness, pain, or rely on cracking for relief, it may be a sign of an underlying biomechanical issue that an osteopath can help assess and treat.

So next time someone warns you about arthritis from knuckle cracking, you can reassure them with science!

References:

• Castellanos, J., & Axelrod, D. (1990). Effect of habitual knuckle cracking on hand function. Annals of Rheumatic Diseases, 49(5), 308–309.

• Kawchuk, G. N., Fryer, J., Jaremko, J. L., Zeng, H., Rowe, L., & Thompson, R. (2015). Real-time visualization of joint cavitation. PLOS ONE, 10(4), e0119470.

• Lederer, S., et al. (1990). Knuckle cracking and hand function: A radiographic study. Arthritis & Rheumatism, 33(6), 810–813.

• Standring, S. (2021). Gray’s Anatomy: The Anatomical Basis of Clinical Practice. Elsevier.

• Unger, D. L. (1998). Does knuckle cracking lead to arthritis of the fingers? Arthritis & Rheumatism, 41(5), 949–950.