Three Reasons Why Joints Crack

Why Joints Crack

Three Reasons Why Joints Crack

Have you ever wondered about the sounds your body makes and why joints crack? As an anatomy teacher, physical therapist and yoga teacher I am often asked, "Why do joints crack?". It is also common for my clients to say, "I know I should stop, but it feels so good!" The truth is, research has not clearly determined if cracking your joints causes any significant harm. To begin with, it is important to understand what is happening when joints crack.

There are three key reasons why joints crack and pop. One very common cause of these sounds is the release of gas that builds up in the joints when they are rest. Do you noticed that after you lace your fingers together and stretch your fingers back into extension to crack your knuckles, it is difficult to recreate the popping noise right away? Do you feel a sensation of pressure relief? If you said yes to these questions, the popping is likely a result of cavitation. Cavitation is a complex chemistry and physics principle that can simply be described as a release of gas. In this case, it occurs in the joints.

Many joints (including those of the fingers) in the human body are considered synovial joints. This means they are surrounded by a joint capsule and a synovial membrane (represented in blue in the picture below) and are filled with clear synovial fluid (represented in black in the picture below). The synovial fluid provides nutrition to the joint as well as shock absorption. When a joint is stretched, the joint capsule is also stretched, causing a decrease in pressure on the fluid filled space. The synovial fluid contains gasses. As the pressure in the joint capsule decreases, the gasses become less soluble and form tiny bubbles. If the pressure is reduced enough (as it likely is with a force on your laced knuckles) the bubbles will pop. Hence, the popping noise. You cannot recreate this popping noise right away because there is a refractory period for the gasses to build back up. That is, it takes some time for new gas bubbles to form before they can be released for another popping noise. The release of the gasses may also stimulate the surrounding nerves which communicate to the surrounding muscles to relax. The "feels so good" sensation is likely a combination of the release of the gas bubbles and a relaxation of the surrounding muscles.
why your joints crack

A second reason why joints crack is related to the tendons. Tendons are the rope-like structures that connect muscles to bones. Tendons cross over joints. As a joint is moved into extreme range of motion, a great amount of force is put on the tendon. In many cases, the tendon crosses over a bony prominence in the joint or other structures that exist in the joint. When they are forcefully pulled or stretched over these structures, a rubbing or snapping may occur. This is what causes the "snap" and "pop" in your joint. There is typically no pain with this type of joint cracking. Also, this type of cracking is easy to reproduce repetitively and without a refractory period. There is no reason to be signficiantly concerned with this type of popping,  particularly if there is no pain. After any type of injury or damage to human tissue, scar tissue builds up. If a joint has been injured or overused, it is likely scar tissue has developed. In a joint with scar tissue, it is very common for the tendons to snap over the scar tissue. Therefore, it is common for clients with a history of injury to report that their previously injured joint "always cracks" now.

The third reason why joints crack may raise concern. If a joint has a significant injury or severe arthritis, the normal alignment of the joint will be lacking. Just as when your car is out of alignment and leads to uneven wear on your tires, so will repeated use of a joint that is not well aligned. It is possible that the cracking noise comes from grinding of structures within an abnormal joint. This type of cracking is often  painful and should be avoided in order to prevent further injury.

Three Key Reason Why Your Joints Crack

1. Cavitation (release of gas bubbles in the joints)

2. Tendons (snapping over structures in the joint)

3. Grinding of abnormal structures or poorly aligned joints

why your joints crack
Avoid Forceful Thrusts
why your joints crack
Choose Gentle Stretches

My general advice to clients who ask if they should stop cracking their joints, is yes. Yet, they may have just heard my lumbar spine "pop" during an easy supine (lying down on my back) spinal twist at the end of my yoga practice. The spinal twist applies enough tension to my spine to release the gasses and relax my muscles. I warn against forcefully rotating at a high speed though. The danger really lies in the forces that a client may make in order to create the popping sound. If a joint naturally pops as you move, there is no reason to be concerned. However, if you bring your hand to one side of your chin and forcefully rotate your cervical spine (neck), it raises concern of putting significant pressure (often in a poorly aligned manner) on the delicate vertebral joints and all of the surrounding structures. Consider choosing some gentle neck stretches instead!  Just as you would care for a brand new car by driving on the paved road, rather then exposing the car to the jolts and stresses of a rocky path, keep your joints on a smooth and easy path too!

Dr. Trish Corley is a Baptiste certified yoga teacher and a doctor of physiotherapy. She leads regularly scheduled yoga classes in Singapore and teacher trainings and workshops globally. 

Are you interested in learning more about Yoga Anatomy or yoga with Trish? Join her for a yoga class or her next yoga event. Check out her calendar!

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