Knee Pain and Popping

By Chloe Wilson, BSc(Hons) Physiotherapy

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

Do you get that snap, crackle, pop in your knees? Knee pain and popping is a common problem.

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 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.

Types of Knee Popping

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.

So let's take a look at what's going on with each one.

Pain Free Knee Popping

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.

Gas bubbles popping is a common cause of noisy knees

1) Gas Bubbles

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.

2) Ligaments/Tendons

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 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, 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

What is It? The ACL (the ligament which sits in the centre of the knee) gets over-stretched and tears, either fully or partially. Sudden knee pain and popping at the time of injury usually indicates a complete tear of thd ACL.

How Does It Happen? 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

Symptoms? 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, there isn't typically any recurrent knee clicking or popping afterwards

Treatment? ACL Injury treatment will depend on the extent of the tear but usually involves exercises, knee braces 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. 

2) MCL Injury

An MCL tear can cause knee pain and popping

What is It? The Medial Collateral Ligament on the inner side of the knee gets over-stretched and tears

How Does it Happen? FThe MCL usually gets torn when a force gores through the outside of the knee e.g. tackle, or sudden twisting e.g. skiing

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

Treatment? MCL tears are usually treated with a combination of knee exercises, tubigrip, knee braces and friction massage

You can find out more about the causes, symptoms and treatment options in the MCL Injury section.

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) Cartilage/Meniscus Tear

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

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 from a meniscus tear 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 about this common cause of knee pain and popping. 

2) Arthritis

What is It? Osteoarthritis is wear and tear of the cartilage that lines the knee joint accompanied by the formation of bone spurs, known as osteophytes

Arthritis can cause knee pain and popping

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? Arthritis is the most common cause of knee pain and popping 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? With arthritis, knee pain and popping, clicking and crepitus tend to be persistent rather than coming and going

Treatment? Exercises, knee brace, injections, surgery

Find out everything you need to know about this causes of a popping knee in the Arthritis section.

3) Chondromalacia Patella

What is It? Chondromalacia Patella is irritation and inflammation of the cartilage lining the back of the patella (kneecap)

Chondromalacia Patella can cause a grinding sensation at the knee

What Causes the Noises? The friction between the back of the kneecap and the underlying femur (thigh bone) seen in chondromalacia patella can cause knee pain and popping 

Who Does it Affect? Healthy, often sporty adolescents and young adults. Chondromalacia Patella is more common in women than men

Frequency? It 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 the knee joint

Treatment? Exercises, knee strap, taping, ice, medication

Find out more about the causes, symptoms and treatment options in the Chondromalacia Patella section.

4) Runners Knee

What is It? 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!

Runners knee

What Causes the Noises? In Runners Knee, 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.

What Do I Do About The Popping?

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

If you would prefer to diagnose your pain using other specific symptoms such as giving way, locking, or pain when running, visit the knee symptoms section. Alternatively if you prefer to think about 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 if you have knee pain and popping. 

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  3. Symptoms
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Page Last Updated: 18/9/18
Next Review Due: 18/9/20


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