The Real Reason Why Your Knees Pop

Ever noticed your knees pop after a long period of sitting down, or even after a good stretch? The sound may be alarming, but it's hardly ever combined with a sudden jolt of pain. This may seem strange, but it's actually a result of a natural occurrence in the body.

Medically referred to as crepitus, this popping sound is actually the result of a gas bubble bursting between the joints when they are moved or stretched rapidly, according to Cone Health. This gas bubble occurs due to a buildup of carbon dioxide in the synovial fluid surrounding the knee joint. This fluid, which surrounds every joint in your body, helps lubricate joints and is made up of oxygen, carbon dioxide, and nitrogen, according to Pinnacle Orthopaedics.

So when you move suddenly from a sedentary position or stretch your legs out in bed, the movement will more than likely be accompanied by this startling sound. While this occurrence usually is no cause for alarm, if it's accompanied by pain, it may be a symptom of other underlying medical conditions.

According to Pinnacle Orthopaedics, pain when your knees pop could be a sign of arthritis. This is a common chronic condition that "causes pain and inflammation in a joint," per the U.K.'s National Health Service, and typically presents itself as osteoarthritis or rheumatoid arthritis.

Osteoarthritis is diagnosed when the smooth cartilage lining of the joint starts to break down. This makes movement harder, and can lead to pain and stiffness due to tendons and ligaments trying to compensate for the loss. Rheumatoid arthritis occurs when the synovium or synovial membrane (via Physiopedia) is attacked by the immune system. This can cause swelling, change in the joint's shape, and may even "cause the bone and cartilage to break down," according to the NHS.

While popping or cracking joints may be a symptom of arthritis, both Cone Health and Harvard Health Publishing say there's no evidence to support the myth that purposely cracking your joints, like the knuckles and knees, will cause the chronic condition.

Another reason why your knees are popping could be the result of your exercise regime. If you focus on a lot of leg-heavy workout routines, you could risk cartilage injury or wear, according to Cone Health, and even a meniscus tear.

A cartilage injury occurs from overuse of the joint, and with the kneecap, this can result in the cartilage softening or wearing away when in contact with the front of your femur (thigh bone). When there's no cartilage there, it begins to hang around the joint and can cause irritation.

A meniscus tear, on the other hand, is when the "rubbery disc that cushions your knee and absorbs shock" is injured. This occurs when your knee is forcibly rotated or twisted with full weight applied. Symptoms of a torn meniscus include a popping sound or sensation, accompanied by swelling, stiffness, pain, and difficulty straightening the knee, according to Mayo Clinic.