Have you ever heard a crackle in your knees as you stood up from a squat? Do your shoulders creak during lateral raises? Or maybe you’ve heard a pop deep inside your hip socket when you ease into Warrior II pose. These cracking, creaking, popping sounds coming from your joints can be disconcerting, even embarrassing, but medical experts say most of them are harmless. Normal movement causes some cracking and creaking in even the healthiest joints and cartilage. Some noises, though, are the result of cartilage damage from injury, loss of muscle tissue, or conditions such as osteoarthritis.
Understanding what causes joint sounds is the first step in determining whether the racket in your body is just incidental noise or something that requires medical attention. In either case, learning how to better support your joints, especially as you age, may quell some of the clatter.
Totally Normal Noises
One of the most common sources of noise is gas—but not the intestinal kind. The joint capsule is filled with synovial fluid, which lubricates the joint and provides nourishment to the cells that form cartilage. The fluid contains dissolved gases, including carbon dioxide, nitrogen, and oxygen. When the joint ligaments are stretched, either intentionally (knuckle cracking) or by accident (arching your back), the pressure within the capsule changes and it releases carbon dioxide in the form of bubbles. The cracking sound you hear comes from those gas bubbles bursting. When these bubbles burst, people experience a sense of spaciousness within the joint and a temporary increase in its range of motion.
Another common cracking or popping sound doesn’t come from within the joint at all. During movement, tendons and ligaments that cross the joint can temporarily shift position or drag across a bone. When they return to their normal position, they make a snapping noise. You may have heard this in your knees when you rose from a sitting position, or in your neck when you turned your head. It’s also common in the shoulders. Loss of muscle mass from aging hastens this effect because more bone is exposed. This sounds scarier than it is; it’s actually a normal and harmless occurrence.
Not-So-Normal Noises
Something called crepitus, on the other hand, is not so benign. It might manifest as a crunching sound when you bend or extend your knees and is often described as sounding like Rice Krispies popping in a cereal bowl. Crepitus occurs when there is damage to cartilage within the joint. Sometimes the damage is due to overuse or aging; sometimes it’s a byproduct of injury, such as a tear in the ligament or cartilage. It can also be an early sign of arthritis.
