People often feel a crackling or popping sensation in the knees during movement. This is generally harmless and can affect any joints. However, people may also experience knee popping and pain which could be a sign of ligament injury, meniscal tear, or patellar tracking problems.

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This article looks at the causes of knee popping and what it means when pain accompanies it, plus when to consult a doctor and seek treatment. We also look at risk factors, tips for healthy knees, and the outlook for people with knee popping.

Knee popping is usually harmless when not accompanied by pain or swelling. The sound and sensation tend to occur because of the structure of the knee. The knee consists of three bones:

  • the kneecap called the patella
  • the shinbone called the tibia
  • the thighbone called the femur

The kneecap sits in a curve in the thighbone called the trochlea. When the knee straightens or bends, the kneecap moves backward and forward inside the trochlea. The trochlea is padded by soft tissue for protection.

When swelling, pain or both accompany knee popping it could indicate injury to the tissues — soft tissue or bone —surrounding the knee, referred to as pathological noise.

Read more about the anatomy of the knee.

Causes of knee popping and pain

Sources of knee popping with pain include:

  • Torn meniscus: The meniscus can tear if someone suddenly rotates or bends the knee with significant force. The injury can cause:
    • a catching feeling or popping sound with movement
    • occasionally pain
    • stiffness and swelling
    • the sensation of the knee giving way
    • inability to move the knee through its full range of motion
  • Cartilage injury: Damaged cartilage can cause popping noises as the knee moves, and can cause inflammation, limited range of motion, and swelling.
  • Patellar tendon tear: The patellar tendon joins the top of the kneecap and shinbone. A torn patellar tendon can cause a popping sound, pain, bruising, difficulty straightening the leg, and an indentation at the bottom of the kneecap.
  • A torn anterior cruciate ligament (ACL): A tear in the ACL, is the most common knee injury, and causes a loud popping noise, typically followed by severe pain and significant swelling. A person may not be able to stand on the affected leg.
  • Lateral collateral ligament (LCL) sprain: This injury may cause a popping sound, pain, stiffness, and weakness.
  • Torn medial collateral ligament (MCL): A tear in the MCL can cause swelling, pain, and a popping noise. The pain ranges from mild to severe depending on whether the ligament is stretched or torn.
  • Posterior cruciate ligament (PCL) injury: An injury to the PCL, may make a popping noise, along with pain and swelling.
  • Patellar tracking impairments: Typically, doctors diagnose people with patellar femoral syndrome when the patella does not track correctly or move up and down in the trochlear groove correctly. People will often experience a grinding, popping, or catching sensation at the patella when bending or straightening the leg.

A person should consult a doctor about a knee popping if:

  • they feel pain and notice swelling
  • they cannot move the joint easily
  • the symptoms have not improved within a few days
  • they cannot relieve the pain with over-the-counter pain relievers
  • there is discoloration or numbness in the knee
  • they cannot stand or put weight on the knee

The treatment of knee popping accompanied by pain will differ according to the cause of the pain and the severity.

Treatment may include:

PEACE and LOVE protocol

Newer management techniques include the PEACE and LOVE protocol. Immediately after an injury a person should:

  • Protect: Restrict movement for 1–3 days. People should minimize rest as prolonged periods can compromise tissue strength and quality.
  • Elevate: Elevate the knee higher than the heart to promote interstitial fluid flow out of tissues.
  • Avoid anti-inflammatories: Inhibiting inflammation using medications may negatively affect long-term tissue healing, especially when doctors prescribe higher dosages.
  • Compress: Apply external pressure using a bandage or taping.
  • Educate: Physical therapists should educate patients on the benefits of an active approach to recovery.

After the first days have passed, soft tissues need LOVE:

  • Load: A person should resume exercise as soon as symptoms allow. People can add optimal loads without exacerbating pain to:
    • promote repair
    • build tissue tolerance
    • enhance capacity of tendons, muscles, and ligaments
  • Optimism: Doctors associate optimistic expectations with better outcomes and prognosis for recovery.
  • Vascularization: People should start pain-free aerobic exercise a few days after injury to boost motivation and increase blood flow to the injured structures and improve physical function.
  • Exercise: Exercises help to restore mobility, strength, and proprioception early after injury. A person should try to avoid pain to ensure repair.

Exercising regularly can help strengthen the muscles around the knees. Physical activity with resistance bands, weights, or movements like lunges and squats and cycling, can help keep knees healthy.

Regular exercise can also help maintain a moderate weight, which can reduce stress on the knee joints. Find out what exercises to avoid and which to try.

Maintaining a stretching routine can also help warm knee muscles up to reduce the risk of injury and improve flexibility.

Read more about knee exercises for strength and flexibility.

Many people experience popping sensations and sounds in their knees.

When pain or swelling accompanies the popping sound, a person may require medical attention. Doctors often do not know the exact causes of knee popping, but typically it results from a meniscus or ligament injury.

Newer treatments consist of the PEACE and LOVE method; protect, elevate, avoid anti-inflammatories, compression, education and load, optimistic, vascularization and exercise. A person may also benefit from rehabilitation, medication, and surgery in severe cases.