My knees are cracking. Is this a disease?

Snap, click, squeak, and rattle... some people's knees are "talkative".

These noisy sounds usually occur when the knee joint is flexed and extended, such as squatting and standing up, walking, or going up and down stairs. In most cases, the knee joint noise is physiological and does not mean that there is a disease, but is just a harmless "nagging".

But some of the sounds are pathological. The "swearing" of the knee is urging you to go for examination and treatment as soon as possible to avoid more serious damage due to delay.

How to tell what your knees are saying requires you to listen like this:

Just hearing a sound is not enough

Current technology cannot immediately determine whether there is a disease or what the disease is just by listening to a "click". However, the characteristics of the sound can give us some clues to help us initially determine whether there is a serious problem behind the knee click.

First recall when your knee started to make noises. If you can't remember, that's OK. Physiological noises usually don't leave a deep impression on people, so they can't remember when they started. Pathological noises often start from an injury, and the first time they made noises is often unforgettable. For example, many people who have ruptured their knee ligaments remember the loud noise at that time.

In addition, physiological noises usually occur occasionally, do not occur again after repeated movements, do not have a specific triggering posture (it does not necessarily occur when you want it to), and do not gradually become louder or more frequent. If the frequency of the noise increases, or even occurs every time a certain posture is performed, then the noise is more likely to be pathological.

Image | pixabay

"Snap" - even healthy knees can make noises

Compared to the sound of knee cracking, people are more familiar with the sound of cracking fingers. If you pull or press your fingers hard, the joint may make a crisp "snap" sound, but if you press the same joint again within a short period of time, the sound will not come out.

A similar sound can also occur in the knee, and the sound comes from small bubbles in the joint fluid. Scientists believe that when the joint flexes and extends, the pressure in the joint cavity changes, and the sound is caused by the sudden formation or rupture of bubbles.

A study performed MRI scans while snapping the subjects’ fingers. Reference [2]

The study found that cavitation and sound occurred simultaneously in the finger joint cavity. Reference [2]

The sound of the cavitation itself does not cause pain. Some researchers have tried to crack their fingers twice a day, only cracking their left hand without touching their right hand. After cracking their fingers more than 40,000 times in 60 years, they found that there was no difference in the joints of the two hands, and they won the Ig Nobel Prize for this (of course, it is still not recommended to crack them hard, after all, some people have broken bones because of this).

When accepting the award, researcher Donald L. Unger said to mothers who oppose finger cracking: I know you can hear me, Mom, you are wrong! | 2009 Ig Nobel Prizes

"Knock" - No serious illness, but be careful

Sometimes, the sound is not so crisp, but a "click" like plucking the strings of a guitar, and you can feel the vibration when you touch your knee.

This type of sound may come from the friction between the tendons and bones around the knee. For example, during knee flexion, the iliotibial band on the outside of the knee is blocked by the small protrusion on the outside of the femur. As the knee flexion angle increases, the iliotibial band is pulled tighter until it suddenly slides over the protrusion and bounces back to its original position with a "click" sound.

During knee flexion and extension, the iliotibial band slides over the lateral epicondyle of the femur | Prof. Bellemans

In addition, friction between other tissues, synovial membrane or physiological folds, excessive meniscus activity, etc. may also make noises during movement.

If there is no pain and no obvious tissue damage, this type of sound cannot be strictly considered a "disease." However, if the knee continues to make noises, the condition may suddenly worsen with increased exercise or a certain movement, causing pain.

When the sound comes from the imbalance of lower limb muscle strength and tendon slippage, stretching and strengthening certain parts may help. Common stretching mainly targets the front and outside of the hip and the back of the calf; common strengthening exercises include elastic band side steps, wide squats, vastus medialis activation, etc. After professional evaluation, targeted training is more effective.

Side step with elastic band | Photo provided by the author

Swelling and pain may indicate a problem

In addition to the sound itself, the most likely indicator of a "real illness" is pain or swelling in the knee joint. Severe swelling can be seen at a glance, with the knee joint becoming noticeably thicker, and even making it difficult to bend the knee or keep the calf close together.

However, when the amount of fluid is low, the appearance changes slightly, and it is easier to find it in this position: sit on the edge of a chair with your legs straight, heels together on the ground, and the muscles on the front of your thighs relaxed. If the depression around the patella becomes flatter and the knee joint looks more "full", there may be fluid accumulation in the knee joint or edema outside the joint. If you are not sure whether it is swelling, it is recommended to go to the hospital for a more accurate examination.

The knee on the right side of the picture is normal, with a clear depression around the patella; the knee on the left side of the picture is swollen and has a smoother surface | wikimedia

The real "sick" knee noise, that is, the pathological noise, has more sources, including the cartilage and synovium inside the joint cavity, the bones, tendons, bursae outside the joint cavity, etc. From the type point of view, the noise may come from acute trauma, chronic degenerative changes, and systemic diseases can also affect the knee joint.

Among them, the common saying "If you continue to do that, you will easily get arthritis when you get old" usually refers to osteoarthritis. The reason why many people are concerned about knee cracking is because they are worried about this disease. Osteoarthritis will make the cartilage in the joints rough and the bones have abnormal protrusions. Therefore, when moving, the bones and the surrounding tissues rub against each other, making a "squeaking" sound. Even if you put your hand on your knee, you can feel the friction between the bones.

Healthy knee vs. knee with severe osteoarthritis | Bioventus

If there is a problem with the meniscus, the "buffer" inside the knee joint, it may get stuck during movement and make a "clicking" sound, such as if the meniscus is born with an abnormal shape (discoid meniscus) or there is damage such as a tear, or functional abnormality.

In addition, incomplete absorption of the internal partition of the knee joint during development, abnormal knee joint movement trajectory, extra-articular ganglion cysts, tendinopathy, structural and functional changes after surgery, and systemic diseases such as rheumatoid arthritis may cause the sound.

At this time, you need to see a doctor for diagnosis first, and then consult an orthopedic, sports medicine or rehabilitation doctor for treatment based on your specific situation, such as changing previous exercise habits, relaxing or strengthening certain muscles, and taking medication, physical or surgical treatment. Don't learn those "one move to eliminate knee noise" tricks, because the source of the noise is different, and there is no treatment method or rehabilitation training that is suitable for everyone.

Knee cracking is a phenomenon. It may be completely normal or it may be a serious problem. You need to find out the cause first before you can decide how to solve it.

References

[1] Song SJ, Park CH, Liang H, Kim SJ. Noise around the Knee. Clin Orthop Surg. 2018;10(1):1-8.

[2] Kawchuk GN, Fryer J, Jaremko JL, Zeng H, Rowe L, Thompson R. Real-time visualization of joint cavitation. PLoS One. 2015;10(4):e0119470.

[3] Schiphof D, van Middelkoop M, de Klerk BM, Oei EH, Hofman A, Koes BW, Weinans H, Bierma-Zeinstra SM. Crepitus is a first indication of patellofemoral osteoarthritis (and not of tibiofemoral osteoarthritis). Osteoarthritis Cartilage. 2014;22(5):631-8.

[4] Bellary SS, Lynch G, Housman B, et al. Medial plica syndrome: a review of the literature. Clin Anat 2012; 25:423.

[5] Unger DL. Does knuckle cracking lead to arthritis of the fingers? Arthritis Rheum. 1998;41(5):949-50.

[6] Maricar N, Callaghan MJ, Parkes MJ, Felson DT, O'Neill TW. Clinical assessment of effusion in knee osteoarthritis-A systematic review. Semin Arthritis Rheum. 2016;45(5):556-63.

[7] Prior J, Mascaro B, Shark LK, Stockdale J, Selfe J, Bury R, ​​Cole P, Goodacre JA. Analysis of high frequency acoustic emission signals as a new approach for assessing knee osteoarthritis. Ann Rheum Dis. 2010;69(5):929-30.

[8] Kalo K, Niederer D, Stief F, Würzberger L, van Drongelen S, Meurer A, Vogt L. Validity of and recommendations for knee joint acoustic assessments during different movement conditions. J Biomech. 2020;109:109939.

Author: Dai Tianyi

Editor: odette

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