Knees that crack and pop are fairly common among athletes and people who exercise. The way the joint works can cause painless cracking sounds during cardio, lunges and other exercises that require your knee to flex and extend. If the cracking sounds are accompanied by pain, you may have a knee injury or condition that requires medical attention, so see your doctor.
Harmless Gas
The most common cause of joint cracking is called “cavitation” – when carbon dioxide come out of the synovial fluid and forms bubbles within cavities in the knee joint. When these cavities close quickly, such as when you extend your knee during cardio activities, the bubbles “pop” and create the cracking sound.
Patellofemoral Syndrome
A less common but more serious cause of knee cracking is from patellofemoral syndrome. This is when the underside of your patella rubs unevenly on the front of your femur. This makes bits of the cartilage that protects the underside of the patella come off in strands, which gets into the joint and may cause grinding, cracking and popping noises when you exercise. This is usually accompanied by mild to severe discomfort. If you experience grinding noises or sensations, your knee collapses unexpectedly -- such as when you are walking up stairs -- or feel pain when your knee cracks, see your doctor.
Other Causes
The movement of the knee joint causes the tendon to move out of place, which might cause a snapping or cracking sound as it returns to its proper position. Another potential cause of knee cracking might be from the ligaments tightening as you flex and extend your knee. Finally, arthritis in the knee can cause uneven surfaces within the joint as the cartilage becomes degraded – this causes cracking and grinding noises as you walk, run and jump.
Treatment
If you feel pain or severe discomfort, grinding or stretching when you hear the cracking sound during cardio exercise, stop your activity immediately. Ice the knee to help reduce or prevent inflammation, and rest the knee to help it heal. Keep that affected knee elevated as much as you can, to reduce any potential swelling. Your doctor may recommend NSAIDs if you experience severe swelling or pain. If you don’t feel pain when your knee cracks, you can probably assume it’s just the harmless popping of gas within the knee and continue with your activities.
Prevention
According to Stronglifts.com, there are several things you can do to try to prevent or reduce knee cracking and to strengthen the knee to avoid injury: strengthen and balance your hamstrings and quadriceps muscles – the muscles that support the knee; perform a proper warm-up before you begin your cardio routine; improve your hip and ankle mobility so that your knees aren’t forced to over-compensate; strengthen the glutes to help loosen your hip flexors – which leads to improved hip mobility; learn to jump properly in order to cushion the knee joint – land with bent knees, not straight; and add omega-3 essential fatty acids to your diet to help provide joint support. You can’t do anything to prevent cavitation cracking, unless you find warming up helps decrease the cracking noises. Do what works best for you.
References
- Strong Lifts; 10 Tips to Stop Your Knees From Popping and Cracking; Mar. 18, 2008
- Library Of Congress, Everyday Mysteries; What Causes the Noise When You Crack a Joint?
- University of Maryland Medical Center; Omega-3 Fatty Acids; June 2009
- FamilyDoctor.org; Patellofemoral Pain Syndrome; December 2010
