Why is it that my knuckles crack?
Professor TONY KOCHHAR examines the causes of this phenomenon and explains when you should be concerned
eVER wondered why your joints pop? Way back in 1947 it was thought that cracking your knuckles made a sound because of the formation of a bubble in joint fluid. A mere 68 years after this theory was first proposed and then discredited, Professor Gregory Kawchuk and his team at the University of Alberta have confirmed it.
He says: “It’s a little bit like forming a vacuum. As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume so a cavity is created and that event is what’s associated with the sound.”
What is happening is that your joints are being expanded when you pop them and as the space within the joint is increased, the pressure within the joint drops.
Due to this pressure drop, carbon dioxide is expelled and this release of gas is what creates the crack or pop that you hear when you crack your knuckles.
Yet these sounds can also be created by ligaments or tendons quickly snapping over bone as does happen in someone with “snapping hip”.
With snapping hip the iliotibial band (a tendon) or tensor fasciae latae muscle on the side of your hip snaps over the femur, creating a snap or popping sound. The reason this muscle or tendon snaps over the hip is usually because they are too tight. With proper stretching or use of a foam roller this can often be resolved.
Another possible reason your joints could be making sounds is due to increased ligament laxity. Some people have inherently looser ligaments than others.
Ligaments provide passive structural support for our joints whereas muscles provide active support for our joints. We can control our muscles but we cannot control ligaments.
A person with increased ligament laxity or looseness makes their joints more susceptible to increased motion within the joint and therefore increased ability to expand, release gas and make a sound.
WILL CRACKING KNUCKLES CAUSE ARTHRITIS?
Your joints, including those in your knuckles, are surrounded by a membrane called the synovial membrane which forms a capsule around the ends of your bones.
Inside this membrane is synovial fluid which acts as a
lubricant and shock absorber so your bones don’t grind together when you move.
Yet if you have osteoarthritis, the cartilage within your joints is progressively being damaged and the amount of synovial fluid is typically reduced as well.
The pain and joint stiffness that you feel is a result of your bones starting to come into contact with each other as cartilage and synovial fluid diminishes.
To date, research has not shown a correlation between knuckle cracking and osteoarthritis in your hands. In one study of more than 200 people the prevalence of osteoarthritis in any joint was similar among those who cracked knuckles and those who did not.
WHEN DO POPPING NOISES INDICATE JOINT DAMAGE?
While those funny popping sounds are probably innocuous, other grinding noises, known as crepitus, can be a sign of damaged cartilage or inflammation.
When cartilage deteriorates it creates a rough surface and can even leave parts of bone exposed. The creak and grind of crepitus occurs when the rough surfaces or exposed parts of bone rub against each other. This is osteoarthritis and the noise is common in the knee and neck. It is often painful.
Unfortunately, once you become aware of these grinding sounds there’s little you can do to prevent further cartilage deterioration.
Osteoarthritis is primarily controlled by your genes, although keeping your weight under control can help reduce symptoms.
Confusingly, your degree of cartilage degeneration may not correlate closely with the amount of pain you feel. It seems to depend on how pain signals are amplified or dampened down in the brain but no one is really sure what influences that. Severely painful crepitus is best checked out by a health professional. In rare cases it can be caused by a fracture – the two broken fragments of bone rubbing together is what makes the noise.
If worn cartilage is the cause, you should try to continue to be as active as possible. Cartilage has a poor supply of blood and relies on movement to obtain nutrients.
The bottom line is noise plus pain is much more likely to be an indication of a problem needing medical input than a noisy joint alone. If in doubt, ask your doctor or physiotherapist to check it out.
Professor Tony Kochhar is a consultant orthopaedic surgeon specialising in shoulder, elbow and upper limb surgery at London Bridge Hospital. He is an expert in keyhole surgery and is a visiting professor of sports science at the University of Greenwich. Visit shoulderdoctor.co.uk for advice.