Knee Popping Sound

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If you hear a popping sound from your knees while walking, running or even just straightening your leg, this could be due to any number of things. In general, the medical term for this type of popping, cracking or snapping is crepitus in the knees.

The good news is that in most cases, a popping sound from the knee is not an indicator of trouble.

However, there are many possible reasons why this may happen, and some of them represent medical conditions that demand attention. This is particularly true when the knee popping sound is accompanied by knee pain or swelling or pain in the adjacent areas.

In this text, we will provide a quick overview of the medical conditions that can cause popping sounds from the knees, together with the other commonly observed symptoms for each condition. We will also provide some advice as to the treatment steps to be taken for each condition, if any are needed.

Possible Causes Of A Knee Popping Sound & What To Do About It

Gas Bubbles In The Knees

It is quite normal for gas bubbles to accumulate from time to time in the synovial fluid present in the knee joint. The purpose of this fluid is to lubricate the joint and allow it to flex and extend without friction or other interference.

However, as you flex the knee, some of the gas bubbles may burst, making a popping sound. There will be no accompanying pain besides the popping. If pain is present, this means that the cause is something different than gas bubbles.

What To Do

As mentioned, this is perfectly normal and you don’t need to do anything about it.

Movement Of Ligaments In The Knee

The ligaments and tendons in the knee are elastic and from time to time may have to stretch slightly as they pass over a small bony protrusion (epicondyle) in the joint.

Once over the protrusion, they then snap back to their normal lengths, making a clicking or snapping noise, much as a rubber band may do. The process is painless and quite normal.

What To Do

This is a normal event and you don’t need to be worried about it.

Knee Osteoarthritis

Knee osteoarthritis is a wear and tear condition caused by breakdown of the cartilage that covers the bone ends in the knee joint (and other joints also). The knees are among the joints most commonly affected by osteoarthritis.

As the cartilage breaks down, the bone ends start to make direct contact with each other as the knee is flexed or extended. Because the joint surface becomes rough, this may produce a scraping, popping or clicking noise from the joint. It will also produce increasing pain (as the condition worsens) as well as knee stiffness.

The pain and stiffness may be at its worst upon awakening in the morning or after a period of rest. Over time, inflammation and knee swelling may also develop, further decreasing the ability to walk or run in comfort.

The result will be a steady decrease in knee range of motion and function over time.

What To Do

Osteoarthritis is an increasingly common problem for people in their 60s and beyond. It is arguably the commonest cause of knee pain and popping in this age group. A doctor can propose a combination of activity modifications, pain relief medication , physical therapy and possibly using an unloading knee brace to help control the pain and preserve knee function and range of motion.

Knee Injuries

Sometimes, knee popping sounds can be the result of an injury suffered in a fall or collision. In other cases, it can be a repetitive stress injury caused by excessive running or jumping during sports activities.

Below are some of the injury-related conditions that can cause your knee to make popping, clicking or scraping sounds:

  • A sprained knee can cause a pop at the time the injury is sustained. However, This will normally be a single pop followed by knee pain, as well as immediate swelling and bruising. The popping will come from tearing or overstretching of the posterior cruciate or anterior cruciate ligament (ACL). With rupture of the anterior cruciate ligament, a single pop is a classical sign. There is no recurrent knee popping or clicking afterwards. Some knee sprains can be due to tearing or stretching of the medial collateral ligament (MCL), and this may also be the cause of knee crepitus. ACL and MCL injuries are the two commonest ligament injuries that cause knee pain and popping;
  • Meniscus tears. The menisci are 2 C-shaped pieces of cartilage that sit between the femur (thigh bone) and tibia (shin bone) and help to prevent the two bones touching each other directly.

Typically, a meniscal tear is caused by twisting the knee while the foot is still planted on the ground. Meniscal tears can cause knee popping or clicking as the joint is flexed or extended. However, this will normally be accompanied by knee pain and joint instability. This pain often gets worse the day after the injury occurs.

In some cases, pieces of cartilage become loose and float around inside the knee. These pieces of loose cartilage can get caught in the knee and make clicking or popping noises as you try to move the joint. The popping tends to come and go as the loose cartilage moves around the joint, rather than being present persistently;

  • Chondromalacia patella is an injury due to damage to the cartilage covering the underside of the kneecap. It too can cause crepitus in the knee, but you will also experience pain that increases with activity. The crepitus is caused by friction between the back of the kneecap and the underlying femur and is usually a constant problem;
  • Patellofemoral pain syndrome is a similar condition and is also known as runners knee. The precise causes are uncertain but it can sometimes produce popping sounds in the knee as well as pain that increases during periods of activity. The patella rubs against the femur causing a grinding sensation when the knee moves. Activity that involves deep knee bends, such as climbing stairs or cycling, will produce particularly severe pain. It does not only affect runners.

What To Do

In most cases, the treatment for these conditions requires rest and refraining from activity that will stress the knee. Icing, compressing and elevating the knee will also be integral parts of the treatment.

Doctors may suggest physical therapy to strengthen the muscles, ligaments and tendons in and around the knee. This is a vital step towards preventing recurrence of the injury and should not be neglected. If the knee clicking and popping is not associated with any pain, often these strengthening exercises are all that is needed for elimination of the problem.

However, if a knee ligament or meniscus is completely severed, doctors will suggest surgery to repair the damage. Floating cartilage pieces inside the knee will also need to be removed by surgical intervention.

Knee braces can be worn to help protect the knee while it heals from these injuries. For example, a hinged knee brace will prevent knee hyperextension and protect damaged ligaments or cartilage while they heal.

Knee Replacement Surgery

In advanced cases of knee osteoarthritis, surgeons may replace the original knee with an artificial one made from metal or plastic. Because there is a limit to the time an artificial knee can last, patients are not often considered for any type of knee replacement below the age of 55 years. After surgery, the patient may start hearing unusual noises from the knee such as clicks or pops.

However, this is not that unusual, nor is it a problem. Indeed, a 2018 study by Pazzinatto, Silva, et al concluded that there is no evidence that knee crepitus among osteoarthritis patients is predictive of the need for  knee replacement surgery in the next 3 years. The authors also concluded that there is no evidence that crepitus is predictive of declines in knee physical function or in overall quality of life.

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