Wednesday, June 22, 2016

Help! Both My Knuckles And My Knees Crack

Message from my patient
Have a look at my patient's reply in the WhatsApp message above when I asked about how her knee was. She came to see me earlier last week for "extreme pain" in her L knee. Couldn't run, couldn't jump.
Have a look at her battle scarred knees
I often get this question from my patients. "My knees keep popping or cracking when I squat, sit to stand etc. Is that a problem"?

I've also had patients ask me about knuckle cracking. Common urban legend suggest that too much knuckle cracking leads to arthritis of the hand joints. Worse still, there are also medical/ health professionals who will suggest that with the clicking/ grinding/ cracking in your joints, you have take glucosamine supplements to prevent osteoarthritis. Do not be fooled. You know my thoughts on glucosamine.

Well, let's settle this once and for all and set the record straight.

Within a joint, the joint space is filled with synovial fluid. The synovial fluid lubricates the joint. It also reduces friction in the joint when you move. There are also gases such as oxygen, nitrogen and carbon dioxide in the synovial fluid.

When you manipulate (crack or pop) a joint, you stretch out the space between the bones that make up that joint. This expanding space creates a negative pressure, causing the synovial fluid and gases to rush there. The larger bubbles collapse into microscopic bubbles, leading to that characteristic popping sound, and that's what you hear. The joint often feels better as the joint space is widened and the bones are repositioned better (*see reference I copied below from the article). The joint often has better range of motion too (see my patient's WhatsApp message above).

Do not mistake joint cracking/ popping or manipulation with joint crepitus. Joint crepitus feels a little like grinding you may hear/ feel when a bone moves against articular cartilage - the lining of the bones. Crepitus happens most often in the knees and has also been described as a crunching, grinding or popping sound. I often tell my patients that crepitus with no pain is usually harmless.

Many of my patients also confuse joint cracking with the snapping sound our tendons make when tendons slide between muscles or over bones. Tendons are like rubber bands stretched between muscles and bones to connect both of them. Hence, when a joint moves, the tendon snaps over the bone and can often make a popping or sliding sound. It's very common to hear these sounds in the knees and ankles when you go from sit to stand, squatting or walking up and down stairs.

There is no need to worry about these crunching, clicking, popping or sliding sounds unless they are accompanied by pain. Now you know.


DeWeber K, Olszewski M and Ortolando R (2011). Knuckle Cracking And Hand Osteoarthritis. J Am Board Family Med. 24(2): 169-174. DOI: 10.3122/jabfm.2011.02.100156.

*During an attempt to crack a knuckle, the joint is manipulated by axial distraction, hyperflexion, hyperextension, or lateral deviation. This lengthens part or all of the joint space and greatly decreases intra-articular pressure, causing gases that have dissolved in the synovial fluid to form microscopic bubbles, which coalesce. When the joint space reaches its maximum distraction (up to 3 times its resting joint space distance), joint fluid rushes into the areas of negative pressure. The larger bubbles suddenly collapse into numerous microscopic bubbles, leading to the characteristic cracking sound. The maneuver leaves the joint space wider than it had been and synovial fluid more widely distributed. The stretching of joint ligaments required to produce the widened joint space also leaves the joint with greater range of motion. 

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