Knee pain and popping is a common problem and can be caused by a number of things. Another term commonly used for popping in the knee is "crepitus", which essentially means a noisy joint, whether it be popping, clicking, cracking or snapping.
Knee popping in itself is very common - many people find their knees make strange noises when they do things such a squatting down or getting up from kneeling. In many cases, it is more of a nuisance than a real problem, but in some cases, it may be a sign of an underlying problem in the knee.
Knee clicking and popping noises in the knee usually fall into one of three categories:
1) Pain-free Popping: Popping noises in the knee often occur without any pain, in which case they are nothing to worry about
2) Painful Popping Noise at time of Injury: Sometimes when the knee is injured e.g. twisting awkwardly, there is a sudden, loud "pop" at the same time indicating damage to part of the knee
3) Recurrent Painful Popping Noises not Caused by an Injury: Knee pain and popping can come on gradually with no obvious cause. It may happen sporadically or frequently depending on the cause.
If knee popping occurs without any associated pain, it is usually due to either a build up of gas bubbles inside the joint which burst, or ligaments/tendons snapping over the joint.
Changes in joint pressure can cause tiny bubbles of gas to slowly form in joints. When these gas bubbles burst quickly, they make a popping sound, in a similar way to when you pop bubble-wrap. The technical term for this is cavitation. There is no harm in this and the myth that it makes you prone to arthritis is unfounded.
Ligaments and tendons are soft tissues that are positioned around all the joints in our body. Sometimes when you move a joint (e.g. your knee), a ligament or tendon may stretch slightly as it goes over a small bony lump and then snaps back into place making a knee clicking sound. Again, there is no harm with this knee clicking if there is no pain, and it doesn’t make you more prone to an injury.
If there is a loud "pop" at the time of injury it usually indicates damage to one of the ligaments. The two most common ligament injuries that produce knee pain and popping are ACL (Anterior Cruciate Ligament) and MCL (Medial Collateral Ligament) injuries.
What is It? The ACL (the ligament which sits in the centre of the knee) gets over-stretched and tears, either fully or partially
How Does It Happen? Blow to the side of the knee, sudden twisting or deceleration, leg bending backwards too far
Symptoms? Approximately 50% of ACL tears are accompanied by a popping sound associated with immediate swelling and pain. The other classic sign of an ACL tear is the knee repeatedly giving way. The knee pain and popping only occurs at the time of the injury, there isn't usually any recurrent knee clicking afterwards
Treatment? Exercises, knee brace and/or surgery
You can find out loads more in the ACL Injuries
section including information on rehab, surgery and how to prevent ligament injuries.
What is It? The Medial Collateral Ligament on the inner side of the knee gets over-stretched and tears
How Does it Happen? Force through the outside of the knee e.g. tackle, or sudden twisting e.g. skiing
Symptoms? Inner knee pain and popping/tearing sensation, swelling, instability, difficulty bending the leg
Treatment? Exercises, tubigrip, knee brace, friction massage
Find out more about the causes, symptoms and treatment options in the MCL Injury
Sometimes knee pain and popping develops over time, without any obvious injury. The knee clicking/popping tends to happen frequently and is usually due to one of these conditions:
What is It? A tear in the meniscus, the special cartilage that lines the joint.
What Causes the Noises? When the meniscus tears, small fragments of it can catch in the knee as it moves which results in knee clicking
Associated Symptoms: knee pain, locking (knee gets stuck), swelling
Frequency? Knee pain and popping here tends to come and go, rather than happening all the time as the torn fragment moves around the joint
Treatment? Exercises or surgery depending on type and severity of tear
Visit the Meniscus Tear section to find out more.
What is It? Wear and tear of the cartilage that lines the knee joint
What Causes the Noises? As the cartilage thins, the joint surface becomes rough and friction occurs between the bones resulting in crepitus
Who Does it Affect? It is most commonly seen in people over the age of 50 and develops gradually over time
Associated Symptoms: toothache type pain, stiffness (particularly in the morning) and swelling
Frequency? Knee pain and popping, clicking and crepitus associated with arthritis tends to be persistent rather than coming and going
Treatment? Exercises, knee brace, injections, surgery
Find out everything you need to know in the Arthritis section
What is It? Irritation and inflammation of the cartilage lining the back of the patella (kneecap)
What Causes the Noises? Friction between the back of the kneecap and the underlying femur (thigh bone) can cause knee pain and popping
Who Does it Affect? Healthy, often sporty adolescents and young adults. More common in women than men
Frequency? Tends to be a more constant problem. The knee clicking/crepitus can usually be felt as well as heard when you put your hand over the front of the knee and bend and straighten it
Treatment? Exercises, knee strap, taping, ice, medication
Find out more about the causes, symptoms and treatment options in the Chondromalacia Patella section.
What is It? A problem in how the kneecap moves which causes an ill-defined ache around the knee aka anterior knee pain or patellofemoral pain syndrome
What Causes the Noises? The patella rubs against the femur which is often associated with a grinding sensation when the knee moves
Who Does it Affect? It is usually worse with prolonged activity e.g. running, coming downstairs or after prolonged inactivity e.g. office workers
Frequency? Knee pain and popping tends to come and go with Runners Knee
Treatment? Exercises, orthotics, ice, rest
Find out everything you need to know in the Runners Knee section.
If you want to know more about these common causes of knee pain and popping including treatment options, use the links above. And remember, if you have knee clicking but it doesn’t cause you any pain, don’t worry. It is usually entirely normal and nothing to worry about. You may find that strengthening your leg muscles actually eliminates the noise – see the strengthening exercises section for ideas on where to start.
If you would prefer to diagnose your pain using other specific symptoms, how the pain started or the specific location of the pain, go to the Diagnose Your Pain section for help working out was is causing your pain and to learn what you can do about it.
The only reliable way to diagnose your particular symptoms is to see a doctor but here I have shared with you the more common causes for knee pain and popping. Always see your doctor for a thorough examination to rule out any serious injury.