Knee Pain and Popping

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Do you get that snap, crackle and pop in your knee? Find out about the most common causes of knee pain and popping

Knee pain and popping is a common problem. It's that tell-tale snap, crackle, pop making your knees sound like a bowl of rice krispies.

Many people find they hear strange noises such as knee clicking 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 popping in itself is very common and can be caused by a number of things. It may be as simple as little bubbles of gas popping in the knee or indicate a problem in the soft tissues such as a ligament tear.

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.

Here we look at the most common causes of knee pain and popping and how to treat them.

Knee Pain And Popping Causes

Knee popping and clicking can be caused by a number of things. It may be something simple like the ligaments catching on a bony lump and "snapping" back in to place or gas bubbles popping. But in some cases, knee popping is linked to a more serious injury such as ligament or cartilage tear.

Knee clicking and popping noises in the knee usually fall into one of three categories:

  1. Pain-Free Popping Knee: 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.

Knee Popping No Pain

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. There is generally nothing to worry about with this type of knee crepitus.

1. Gas Bubbles Popping

Gas bubbles popping is a common cause of noisy knees

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 case of knee popping no pain, and the myth that it makes you prone to arthritis is unfounded.

2. Knee Ligaments/Tendons Snapping

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 type of knee clicking if there is no pain, and despite what people often say, it doesn’t make you more prone to knee problems.

Knee Popping with an Injury

Was there is a loud "pop" as you twisted or bent your knee? Knee popping pain at the time of injury 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, usually caused by twisting the knee awkwardly.

1. ACL Injury

ACL injuries are normally associated with knee pain and popping at the time of injury

Sudden knee pain and popping at the time of injury usually indicates a complete tear of the ACL, the ligament which sits in the center of the knee. 

The ACL typically gets damaged when there is a hard blow to the side of the knee (e.g. sporting tackle), sudden twisting or deceleration, or when the leg bends backwards too far which over-stretches and tears the ligament, either fully or partially. 

Approximately 50% of ACL tears are accompanied by a popping sound at the knee 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 usually only occurs at the time of the injury, and there isn't typically any recurrent knee clicking or popping afterwards.

Find Out More: ACL Injuries - Causes, Symptoms & Treatment

2. MCL Injury

An MCL tear can cause knee pain and popping

Another possible cause of knee pain and popping is an MCL tear, where the ligament on the inner side of the knee gets over-stretched and tears.

The MCL usually gets torn when a force gores through the outside of the knee e.g. tackle, or sudden twisting e.g. skiing

Typical symptoms of an MCL tear include inner knee pain and popping/tearing sensation, swelling, instability, difficulty bending the leg

Find Out More: MCL Injuries - Causes, Symptoms & Treatment

Ongoing Knee Pain and Popping

Sometimes knee pain and popping develops over time, without any obvious injury. In these instances, the knee clicking/popping tends to happen frequently and is usually due to one of these conditions: 

1. Knee Cartilage Tear

A meniscus tear can cause knee pain and popping with the torn flap of cartilage getting stuck

Ongoing knee pain and popping is often the result of a tear in the meniscus, the special cartilage that lines the joint. When the meniscus tears, small fragments of it can catch in the knee as it moves which results in knee clicking.

Knee pain and popping from a meniscus tear tends to come and go, rather than happening all the time as the torn fragment moves around the joint. Meniscus tears are often associated with knee locking, where the knee gets stuck and can't bend. 

Find Out More: Meniscus Tears: Causes, Symptoms & Treatment 

2. Knee Arthritis

Arthritis can cause knee pain and popping

The most common cause of knee pain and popping in people over the age of 60 is knee arthritis. With arthritis, there is wear and tear of the cartilage that lines the knee joint accompanied by the formation of bone spurs, known as osteophytes.

As the cartilage thins, the joint surface becomes rough and friction occurs between the bones resulting in crepitus and knee popping pain. 

People with knee arthritis also complain of a toothache type pain, knee stiffness (particularly in the morning) and swelling.

With arthritis, knee pain and popping, clicking and crepitus tend to be persistent rather than coming and going.

Find Out More: Knee Arthritis - Causes, Symptoms & Treatment

3. Chondromalacia Patella

Chondromalacia Patella can cause a grinding sensation at the knee

Chondromalacia Patella is a common cause of knee pain and popping in healthy, often sporty adolescents and young adults.

With chondromalacia, there is irritation and inflammation of the cartilage lining the back of the patella (kneecap). This causes friction between the back of the kneecap and the underlying femur (thigh bone), producing a popping or grinding noise. 

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 the knee joint and tends to happen anytime you bend your knee.

Find Out More: Chondromalacia Patella: Causes, Symptoms & Treatment

4. Runners Knee

Runners Knee is a problem in how the kneecap moves which causes an ill-defined ache around the knee aka anterior knee pain or patellofemoral pain syndrome. It doesn't just affect runners though!

In Runners Knee, the patella rubs against the femur which is often associated with a grinding sensation or popping noise when the knee moves.

Symptoms are usually worse with prolonged activity e.g. running, coming downstairs or after prolonged inactivity e.g. office workers

Knee pain and popping tends to come and go with Runners Knee, rather than happening all the time.

Find Out More: Runners Knee - Causes, Symptoms & Treatment

Knee Popping Treatment

Treatment for knee pain and popping will depend on the underlying cause of the noises, but will generally include strengthening exercises, physical therapy and possibly wearing a knee brace. In some rare cases, knee surgery may be required.

You can find out loads more about these common causes of knee pain and popping including the best treatment options for each, by using 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.

Knee Popping By Activity

Knee Popping When Extending: Knee popping when you straighten your knee is usually due to gas bubbles (not usually painful), plica syndrome or patellofemoral pain syndrome.

Knee Popping and Pain When Bending: If you get knee popping and pain when bending your knee e.g. squatting down, it is most likely due to a problem with the knee cartilage such as a meniscus tear or chondromalacia patella.

Knee Popping When Extending And Bending: If you get knee pain and popping with both knee flexion and extension, it is likely that there is damage to the joint surface such as cartilage damage or knee arthritis. If there is no pain, it is likely to be gas bubbles popping.

Knee Popping With Twisting: Sudden knee pain and popping when you twist is usually doe to a knee ligament injury, most often an ACL injury and/or MCL tear. If the knee swells up or feels unstable after hearing a pop as you twisted, seek medical attention immediately.

Knee Popping When Walking: Almost all the possible causes of knee popping that we've looked at here can cause knee pain and popping when walking, be it arthritis, runners knee, cartilage tear or ligament injury. There will usually be other symptoms associated here that will lead to a clearer knee pain diagnosis.

Knee Popping No Pain: If there is no pain with your knee popping, chances are it is a simple case of gas bubbles bursting inside the joint which is completely harmless. Keeping active and strengthening the knee muscles can sometimes help to reduce the frequency of knee popping.

Frequently Asked Questions

Will Knee Popping Go Away?
In most cases, knee pain and popping will settle down, but how long this takes will depend on what is causing the popping noise. Soft tissue injuries usually heal in 6-12 weeks. Most people notice their knee popping settles down within 3 months of working on knee strengthening exercises. 

If there is no pain with the popping, then it is highly likely the popping noises will continue as there isn't a mechanical problem to be fixed. But rest assured, there is no increased risk of knee problems later in life.

Is Knee Popping Bad?
In most cases, knee popping is not a serious problem, it is simply bubbles of gas popping, or tendons snapping over small, bony lumps.

However, knee popping can be serious if there is a sudden popping noise from the knee at the time of injury, which typically indicates a significant injury to one of the knee ligaments.

Why Do Knees Crack When Squatting?
Many people complain of popping, cracking, or crunching noises when they squat down. The technical term for this is cavitation or crepitus, which simply put means "joint noise". Caused by a change in pressure inside a joint, gas bubbles of carbon dioxide form, and when they burst, you get the familiar cracking sound in your knee. 
RELATED ARTICLE: Knee Pain When Squatting

How Do I Crack My Knee Safely?
If your knee feels like it locks up sometimes, you may find that releasing the pressure in the joint helps. This is only appropriate if there is no knee pain and you have not recently injured your knee.

  • Lie down somewhere comfortable 
  • Stretch your leg out until your knee is straight, toes pointing towards the ceiling
  • Keeping your leg straight initially, lift your leg up as high as is comfortable and then slowly bend your knee in and out until you hear a small pop.

The best 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 if you have knee pain and popping.

Page Last Updated: 10/07/21
Next Review Due: 10/07/23


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References

1. Clinics In Orthopedic Surgery Journal: Noise around the Knee. February 2018

2. WikiHow: How to Keep Your Knees from Popping and Cracking. July 2018

3. Physical Therapy In Sport: Implications of knee crepitus to the overall clinical presentation of women with and without patellofemoral pain. September 2018

4. Musculoskeletal Science and Practice: People's beliefs about the meaning of crepitus in patellofemoral pain and the impact of these beliefs on their behaviour: A qualitative study. April 2017