Most of your life you've noticed it: Your knee sometimes makes a popping sound when you bend it, or crouch, or climb steps, or just shift your weight. As you get older, it seems to be happening even more often. Is this an indication of something wrong with your knee?
Normal Knee Noises
Just like your knuckles, your shoulders and your ankles, your knees can generate a popping sound even when nothing's wrong in there. The medical term 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. (Note: this word is similar to crepitation, which describes a crackling sound in a diseased lung - not to be confused with the usually harmless pops that can come from your knees and other joints.)
What Causes My Knee to Pop?
Your knee joint is a complex hinge, formed by the intersection of the three leg bones: the femur (or thigh bone), the tibia (the shin bone), and the fibula (the smaller of the two lower leg bones). Protected by the kneecap (the patella), the moving parts of the knee joint operate smoothly, cushioned by pads of springy tissue called the menisci, and oiled by a natural lubricant called synovial fluid. As your 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 you get. There's 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 cartilage that covers the ends of the leg bones at the knee joint can contribute to crepitus accompanied by pain. Sometimes, often in younger people, this kind of damage results from a sudden twist or impact due to vigorous activity like sports. Sometimes a piece of cartilage can detach and interfere with the action of the knee joint, causing pain, swelling, crepitus and a 'catching' when you bend your knee.
Meniscus Tear - In your knee joint are two C-shaped discs knows as menisci that act as shock absorbers or cushions for the joint, and help distribute your weight in a balanced way. If trauma (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 you knee.
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, NSAID pain relief, rest and possibly a knee brace and physical therapy are among the remedies you might be offered. In extreme or progressive cases, your doctor might recommend partial or total knee replacement surgery, to implant a mechanical joint in place of damaged ends of the femur, the tibia of the fibula. Some 600,000 knee replacements occur yearly, with a success rate in the range of 90 - 95%.
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 you can do to help avoid hurting your knee. Dietary supplements like Glucosamine and Omega-3 fatty acids have some, mostly unproven positive effect. Keeping the muscles that support your knees in good tone is essential, and the exercise you invest to accomplish that can be beneficial to your overall health and longevity.