Few things are more disconcerting than the loud crack our joints occasionally release when we sit, stand, or otherwise bend. It’s unnerving and if you’ve just started to notice your joints making a popping or cracking noise with movement, or you’re one of those people who has a habit of cracking your knuckles, you may wonder what causes your joints to make that noise with movement. Most of us have experienced a popping or cracking noise (termed “crepitus”) at times when getting up from a sitting or kneeling position. And, while a bit unpleasant sounding, in most instances, it’s not a sign of joint issues and is just a normal response to joint movement.
The joints that most commonly “crack” with movement are called diarthrodial joints. They are comprised of a capsule containing two bones that move along their cartilage surface. These include, for example, your knee and finger joints. The joint capsule contains synovial fluid which provides slip to the joint and nutrients. There are also gases (oxygen, carbon dioxide, and nitrogen) that are dissolved in the fluid.
So, what causes the cracking sound?
There’s been quite a bit of controversy over the years regarding what is creating that popping and cracking sound in the joint. Theories range from compression of nitrogen gas in the joint to ligaments or tendon movement. When a joint is cracked, the gasses within the joint increase in volume and form a bubble. There are theories that the formation of the bubble causes the noise. Meanwhile, others point to the collapse of the bubble. Once the joint is cracked the gases dissolve back into the fluid, but this can take up to twenty minutes. It may be the reason why you can’t crack the same knuckle two times in a row.
Another possible cause of joint snapping or cracking may be related to joint soft tissue. When tendons move over the joint, they may make a snapping noise as they move against bone and muscle or as the tendon rebounds after movement.
A recent study attempted to answer the cracking joint question. It used MRI to visualize a finger joint as it’s being cracked. The researchers found that as the joint was cracked, a gas bubble formed in the cavity created where the joint was separated, resulting in the cracking sound. The researchers suggested that the noise may be associated with the pressure change and bubble formation within the joint as it’s being cracked.
Beyond the irritating sound, is a cracking joint a sign of an issue with the joint? Cracking your knuckles feels good because manipulating the joint causes relaxation of surrounding joint muscle. This gives the sense that your joint can move more freely.
So, is it a bad sign if my joints crack?
There’s been concern that there’s an association between habitually cracking your knuckles and the development of arthritis. This concern isn’t supported by the research. In studies that examined radiographs of the knuckles of those that habitually cracked their hand joints, with those didn’t, no difference was found in the rate of osteoarthritis between the two groups.
Cracking your knuckles may not lead to osteoarthritis. However, several studies have found an association between chronic hand joint cracking and both increased hand inflammation and reduced grip strength. It’s not known what may cause this finding, but if you’re a habitual knuckle cracker, knowing that there’s a risk of injuring the soft tissue surrounding the joint may help you curb this habit.
Jacqueline D. Kimble, PT, OCS, says that, in most cases, joint cracking doesn’t signal an injury or other worrisome process going on. The cracking may be a sign of some normal wear and tear in the joint. As we age, our joints degenerate and lose their joint cushioning. The knee joint cracking you experience when standing from a seated or squatted position may be from degenerating rough joint surfaces rubbing against each other.
If joint cracking is becoming more frequent, try focusing on stretching. Kimble says that she sees clients who have joint cracking that’s related to tight muscles. She says that tight muscles can rub and cause friction around the bone. This can cause the joints to crack as they move. She has her clients incorporate gentle stretching. This may help to decrease the frequency of joint noise and allow them to move more freely.
Most joint noise is a normal part of joint articulation. But the following warning signs may point to a more serious issue that should be followed up with your health care provider.
- Joint noise associated with pain may be a symptom of joint surface damage, such as tears in cartilage, or the onset of bursitis or tendinitis.
- Sudden onset joint clicking, snapping, or cracking—especially in the shoulder joint—may be a sign of joint instability.
- Redness or swelling of the joint may signal of injury or infection.
If you notice any of the above symptoms, make an appointment with your doctor.
Catherine Cram is an exercise physiologist and a leading expert in the field of maternal fitness. Her consulting company, “Prenatal and Postpartum Fitness” specializes in providing the most current maternal exercise information and continuing education courses to health and fitness professionals.