What's That Popping Sound In My Knees?
Many people go about life accustomed to the fact their knees sometimes make a popping sound. Often there isn't really much discomfort, and they barely notice, but when they bend their knees, or crouch, or climb steps, or just shift their weight, there's a faint pop or crackle. Some people notice that the noise increases, along with pain, as they get older.
Normal Knee Noises
Just like your knuckles, shoulders, and ankles, the knees can generate a popping sound even when nothing's wrong. The medical term for this is crepitus, which refers to grinding, cracking or popping sounds emanating from under the skin and joints or a crackling sensation due to the presence of bubbles of air under the skin.1 (Note: This word is similar to crepitation, which describes a crackling sound in a diseased lung - crepitation is much more serious and should not to be confused with the pops that can come from the knees and other joints.)
What Causes the Knee to Pop?
The knee joint is a complex hinge, formed by the intersection of the three leg bones: the femur (thigh bone), the tibia (shin bone), and the patella (knee cap). In a healthy knee, the moving parts of the joint operate smoothly, cushioned by pads of springy cartilage tissue called the menisci, and sliding on a slick tissue called articular cartilage, which is oiled by a natural lubricant called synovial fluid. As the knee flexes, small bubbles of gas can form in the fluid, and become compressed over time. It's the shifting and popping of the bubbles that creates the popping noise and the sensation of relief some people feel. There's a term for the bubble popping too: Cavitation. This is all normal - unless it hurts.
What If the Popping Causes Pain?
If the popping or grinding is accompanied by pain, you may have a problem that calls for medical attention. When pain enters the picture, these are some of the possible causes:
Cartilage injury: Damaged to the articular cartilage that covers the ends of the leg bones at the knee joint can contribute to crepitus accompanied by pain. This kind of cartilage damage may result from a sudden twist or impact due to vigorous activity like sports. Most often this is caused by a piece of cartilage that detaches and interferes with the action of the knee joint, leading to pain, swelling, crepitus (popping sound), and a 'catching' sensation when bending the knee.
Meniscus tear: In the knee joint, there are two C-shaped discs known as menisci that act as "shock absorbers" or cushions for the joint and help distribute force and weight in a balanced way. If trauma (such as from a fall or a sporting injury) causes damage to the menisci, the result can be crepitus, accompanied by swelling, pain, and a tenderness that makes it difficult to put weight on the knee.2
Osteoarthritis (OA): As we age, the knee cartilage can grow thinner or break down due to wear, causing a painful grinding sensation along with crepitus. Initial treatment after a diagnosis of OA is typically conservative: Ice pack, over-the-counter pain medications, rest, physical therapy, and possibly a knee brace are among the typical remedies. In extreme or progressive cases, a doctor might recommend partial or total knee replacement surgery to replace the damaged ends of the femur (or tibia). Some 600,000 knee replacements occur yearly, with a success rate in the range of 90 - 95%.3
What You Can Do to Avoid Knee Pain
While there's not a lot of help for normal popping in the knee that is not accompanied by pain, there a few things that may help avoid hurting your knee. Dietary supplements like Glucosamine and Omega-3 fatty acids may have some, mostly unproven, positive effect. Keeping the muscles that support the knees in good tone is essential, and the exercise invested to accomplish that can be beneficial to overall health and longevity.4
The information in this article is for informational and educational purposes and is not meant as medical advice. Every patient's case is unique and each patient should follow his or her doctor's specific instructions. Please discuss nutrition, medication and treatment options with your doctor to make sure you are getting the proper care for your particular situation.