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Why Do the Knees Click When You Bend or Straighten Them?

Clicking or popping in the knees when we are bending or straightening them is quite a common occurrence. Medically, this clicking of the knees is known as knee crepitus, which means a noisy joint. There are different causes for clicking of the knee when it is flexed or extended. Some of the common causes include stress or injury to the knee joint or the leg. Depending on the cause of knee clicking and the extent of injury, treatment is done. Some patients will experience knee clicking after an injury, which is also accompanied by pain upon movement. Some patients experience knee clicking only and this occurs as a result of improper positioning of some part of the knee leading to increased stress/strain on other parts of leg, which produces the clicking noise.

Why Do the Knees Click When You Bend or Straighten Them?

Why Do the Knees Click When You Bend or Straighten Them?

Some of the causes or conditions which cause the knees to click upon bending or straightening include:

Knee clicking commonly falls into one of three categories given below:

Pain-Free Knee Clicking: Patient has knee clicking without any pain. In such cases, this is not a cause for concern.

Painful Knee Clicking With Injury: In some cases, when the patient has injured the knee, by twisting it awkwardly, then there would be an abrupt “click” or a “pop” heard, which indicates that some part of the knee has been damaged.

Recurrent Painful Knee Clicking Without Injury: Some patients can gradually develop knee clicking without any apparent cause.

Causes of Pain Free Clicking of the Knees When Bending or Straightening Them

If there is clicking of the knee without any pain, then it commonly occurs from bursting of the accumulated gas bubbles within the knee joint, or snapping of the tendons/ligaments over the knee joint.

Gas Bubbles: Bursting of the gas bubbles is one of the common causes of clicking in the knees on bending or straightening them. There is gradual formation of gas bubbles in the knee joint from changes in joint pressure. When these gas bubbles burst suddenly they result in a popping sound or a clicking sound. This is completely harmless and does not require treatment and does not predispose the patient to arthritis in any which way.

Snapping of Tendons/Ligaments: Tendons and ligaments are the soft tissues that are present around the joints. When there is movement of a knee joint or any other joint, it causes stretching of the tendon or ligament when it passes over a small bony bump; after which the tendon or the ligament snaps back into its place resulting in the clicking sound in the knee joint. This is also a harmless condition and does not need any treatment nor does it increase the risk of the patient towards any knee injury.

Causes of Knee Clicking with Injury

If the patient has loud clicking or a popping noise from knee during injury then it often indicates a ligament injury. There are two common ligaments which produce knee clicking and pain when they get injured and these ligaments are:

Anterior Cruciate Ligament (ACL) Injury: ACL injuries usually cause knee pain with clicking or popping at the time of injury. There is overstretching of the ACL at the centre of the knee which causes it to tear. ACL injury can occur from a blow to the lateral part of the knee, sudden deceleration/twisting of the leg or knee, or when the leg gets bent backwards extensively. Half of the patients with ACL injuries will have knee clicking at the time of injury along with pain and swelling. The affected knee can also give way when standing.

Medial Collateral Ligament (MCL) Injury: Overstretching of the Medial Collateral Ligament present on the inner side of the knee causes it to tear. MCL tear can occur as a result of sudden force to the outside of the knee such as during tackling in football games or sudden twisting of the knee which can occur when skiing. Along with knee clicking, patient also experiences pain in the inner side of the knee, swelling, tearing sensation, difficulty bending the leg and instability of the knee joint.

Causes of Recurrent Painful Knee Clicking Without Injury

Sometimes a person can develop knee clicking along with pain over a period of time, without any apparent injury. The cause for such type of knee clicking can be:

Cartilage/Meniscus Tear: Meniscus or cartilage tear can also cause pain and clicking of the knee on bending or straightening them. When the meniscus gets torn, torn fragments of it may get stuck in the knee with movement resulting in the knee clicking when a person bends or straightens. The knee clicking may not always be present and can come and go as the torn fragment moves around the knee joint.

Arthritis: Arthritis of the knee joint can also cause pain and clicking in the knee. Arthritis is a condition where there is wear and tear of the cartilage around the knee joint. There is thinning of the cartilage and surface of the joint becomes rough due to which there is friction between the bones resulting in clicking sound in the knees. People above 50 years of age will gradually develop arthritis as this is a degenerative condition. There is persistent knee clicking in people suffering from arthritis.

Chondromalacia Patella: This is a condition where there is inflammation and irritation of the cartilage which lines the patella. This is due to friction between the posterior side of the kneecap and the underlying femur resulting in pain and clicking in the knee joint. Young adults and sports people are more often affected by Chondromalacia Patella. The knee clicking/crepitus can also be felt when a hand is placed on the knee when bending and straightening it.

Runners Knee: In this condition, the kneecap is out of alignment and does not track along with the femur resulting in anterior knee pain and knee clicking with movement. In this condition, there is rubbing of the patella against the femur resulting in a grinding sensation and clicking in the knee with movements. Prolonged activity, such as running worsens this condition. Movement after prolonged inactivity also worsens this condition. The clicking in the knee comes and goes.

What to do if the Knees Click When You Bend or Straighten Them?

If the knee clicking is not causing any pain or hindrance in daily movements, then it is not a cause for concern. It the patient has difficulty in moving and also has other symptoms such as pain and swelling in the knee joint, then it is important to seek medical attention immediately. Treatment will depend on the cause of the knee clicking and includes: rest, medicines, exercises physical therapy etc.


  1. National Institutes of Health (NIH): “Burn injuries of the knee”: https://pubmed.ncbi.nlm.nih.gov/25934763/
  2. American Academy of Orthopaedic Surgeons: “Common Knee Injuries”: https://orthoinfo.aaos.org/en/diseases–conditions/common-knee-injuries

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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 24, 2023

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