What's happening when your knee goes snap, crackle, and pop
A question I am asked a lot is, “I hear clicking and popping in my knee, is this something that I should be concerned about?”
Joint noise in the form of crackling, clicking or popping is very common. It may be from simple soft tissue catching or more serious damage to the bearing surface of the joint, the articular cartilage. What I tell my patients is that unless it is causing pain, swelling or the knee is giving way, it is nothing to worry about. If it’s painful, then I’ll investigate further.
No worries: Sometimes this noise is due to tiny air bubbles inside the joint fluid, which build up with changes in joint pressure. The bubbles make a noise when they burst. This is called cavitation. Another cause for painless popping in the knee is when the ligaments and tendons catch as they go over a bony lump and pop when they snap back into place. Or the clicking and popping may be caused by catching on soft tissue or scar tissue within the knee. Most of the time these noises are natural and do not mean that you will develop arthritis or be prone to injury.
Some concern: However, when the popping sounds are accompanied by swelling and pain, or they produce a catching sensation or the knee gives way, then those are times when we worry about a possible injury within the knee. A physician should examine the knee to help make a clear diagnosis.
There are a number of possible explanations for the popping. The noise and pain may be a mechanical symptom, which feels like something is caught in the knee as it moves back and forth. This kind of popping is often a sign that you have a meniscus tear or that a small piece of loose cartilage is caught in the knee. You would most likely feel this kind of popping pain come and go.
Painful popping could also be because of osteoarthritis, where the smooth cartilage has worn down and the bones cause friction when they rub against one another. This painful popping would be more persistent.
Another common problem that results in a popping or grinding sensation is roughness on the undersurface of the patella that used to be called chondromalacia and is often labeled as patellofemoral pain syndrome, or runner’s knee. Often you may feel the popping, grinding or crunching more than you can hear it. To feel this, try squatting with your hand flat over the front of your knee.
Real worry: When a patient says to me, “Doc, I heard a pop and my knee swelled,” it is definitely a cause for concern. If there is a pop at the time of injury, the knee has almost certainly been damaged in this case. You have most likely injured either your ligaments — anterior cruciate ligament, posterior cruciate ligament or medial collateral ligament — or the meniscus or articular cartilage. The knee will usually swell up with these kinds of injuries.
If there is pain, swelling or giving way of the knee, then we will do a careful exam, history, and, very often, an X-ray and/or an MRI to study the cartilage and the soft tissue within the knee and determine if the tissues need to be repaired. If the important tissues of the knee are torn, then we will plan to repair that tissue. Sometimes careful physical therapy alone can fix the problem and help you avoid surgery.
So remember, if you hear clicks and pops in your knee but feel no pain or swelling, don’t worry. It is normal. If you have pain, instability or swelling, make sure you check it out to avoid further damage to the joint. The philosophy on this has changed from “rest your knee and wait until you are older for a joint replacement” to fixing the problem by repairing or replacing the missing cartilage so that you may never develop arthritis or need a knee replacement.
If you are experiencing undiagnosed knee pain, use our self-diagnosis symptom checker tool to learn more about your injury.