Knee pain and "noisy" knees are two common reasons that patients often go see a physical therapist. Popping or cracking, and in some cases pain while or after performing knee-dominant movements like split squats, leave them wondering if they should be concerned. The answer, as with so many other things in life, is that it depends.
The technical term for popping is crepitus, and there are a number of reasons that the knees may pop.
Sometimes the popping and cracking is not cause for concern. The knees often pop when bending and straightening, especially during weight bearing activities such as stairs or squats. The popping is usually not painful, and is caused by bursting nitrogen bubbles in the synovial fluid when force is applied to the joint. The technical term for this is cavitation, and it is what happens when you pop your knuckles.
In other instances, the popping noise can come from the joint. The cartilage on the ends of the femur, the tibia, and/or the patella (knee cap) can wear down, and this degeneration of the cartilage causes rough spots which may pop or crack with movement. Many times this isn’t painful; but, sometimes it is. With advanced osteoarthritis, many patients complain of pain, as they have lost the cushioning of cartilage and often feel bone rubbing on bone.
When the cartilage on the undersurface of the patella (knee cap) degenerates, it is referred to as chondromalacia patella. This can be the source of popping noises as you bend and straighten the knee, since the patella is rough and doesn’t glide in its track.
In some people it is very loud but not painful, and in others it only makes a little bit of noise, but is painful. Pain may not occur every day.
Most cases of chondromalacia develop over time; but, some people are born with natural anatomic variations that make them more prone to developing it. In some cases, the issue can be brought on by a trauma to the knee, such as a fall on the patella, where the cartilage is bruised or chipped.
Another possible cause of popping in the knee is a tear in the meniscus, the cartilage that cushions the joint. The tear can happen as a result of a sudden twist, or it can happen because of degeneration of the cartilage over time.
Patients often complain of "locking" in the knee with a meniscus tear, and sometimes there is associated swelling. Pain is often felt at the joint line, between the femur and tibia, in contrast to the pain felt under the kneecap in chondromalacia.
It’s impossible to tell what is truly causing a person's knee symptoms without an examination. If you have popping and cracking, but you don't have an injury or swelling and don't experience locking of the knee, my best recommendation is to see a physical therapist who can evaluate your knee and watch you perform some movements, like a squat, a split squat, and a step up. A physical therapist an make recommendations based on their observations, in order to keep you doing the things you love to do.
Treatment may include mobility exercises, specific strengthening for weak muscles around the hip, and manual therapy. We will work with you to develop a plan to reach your goals. You can locate a physical therapist via the American Physical Therapist Association website.
Note from GGS: We strongly recommend including injury prevention strategies in your training program to address mobility, stability, and overall movement.
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