Hearing a click or pop when you bend your knee, climb the stairs or stand up can be unsettling. You may also notice your knee catching during movement, feeling as though it might give way or becoming temporarily stuck.
But what does it mean when your knee clicks, pops or locks?
Occasional, painless clicking is common and does not necessarily indicate a problem. However, clicking accompanied by pain, swelling, instability or restricted movement may need medical assessment.
The cause can range from normal joint movement to a knee injury or osteoarthritis. Understanding the difference can help you recognise when to seek advice.
Why does my knee click or pop?
Your knee is a complex joint involving bones, cartilage, ligaments, tendons and muscles. These structures work together to support your weight and allow your leg to bend and straighten.
A clicking or popping sound can occur for several reasons. Sometimes, it happens without any underlying injury or condition. In other cases, it may be associated with changes within the joint or damage to one of its structures.
According to the NHS guidance on knee pain, painless clicking is usually normal. Painful clicking, locking or giving way, however, warrants urgent medical advice.
Common reasons for knee clicking include:
- Normal joint movement: You may hear occasional clicks as you bend or straighten your knee without experiencing pain or swelling.
- Knee osteoarthritis: Changes within the joint can cause a grating, crackling or clicking sensation, often alongside pain and stiffness.
- Meniscus injury: Damage to the cartilage that cushions the knee may cause clicking, catching, swelling or difficulty moving the joint.
- Other knee injuries: Damage involving ligaments or other structures may cause a popping sensation, particularly during a sudden twist or change of direction.
The sound alone cannot reliably identify the cause. Other symptoms, your medical history and the circumstances in which the clicking occurs all help determine whether further assessment is needed.
What causes a knee to lock?
A locked knee is different from a knee that simply clicks or feels stiff.
True locking occurs when your knee becomes stuck in a particular position and you cannot fully bend or straighten it. This may happen if something within the joint interferes with its normal movement.
One possible cause is a torn meniscus.
The menisci are two pieces of cartilage inside the knee that help distribute weight and absorb forces during movement. A tear can occur during a twisting injury, although changes to the meniscus can also develop gradually.
As the NHS explains in its guide to meniscus tears, symptoms can include pain, swelling, difficulty bending or straightening the knee, clicking and a feeling that the knee is giving way.
Other knee conditions can also cause catching or restricted movement, so locking should not automatically be attributed to a meniscus tear.
If your knee has suddenly locked and you cannot straighten it, seek urgent medical advice. Do not try to force it straight.
Why is my knee giving way?
If your knee feels as though it might buckle beneath you when you stand, walk or climb stairs, you may describe it as giving way.
This sensation can have several causes, including:
- Meniscus damage: A tear may cause pain, catching or a feeling of instability.
- Ligament injury: Ligaments help stabilise the knee. An injury can affect how securely the joint supports movement.
- Knee osteoarthritis: Pain, stiffness and weakness around the joint can sometimes contribute to a feeling that the knee is giving way.
- Muscle weakness or pain: Changes in muscle strength or the way you move because of discomfort may affect your knee’s stability.
The NHS guidance on osteoarthritis symptoms identifies grating sensations, stiffness, reduced movement and occasional giving way among possible symptoms affecting the knee.
However, these symptoms do not establish a diagnosis on their own.
If your knee repeatedly gives way, particularly if you are falling or struggling to walk safely, arrange a medical assessment. If it happens after an injury or alongside severe pain or swelling, seek urgent advice.
Could knee clicking be a sign of osteoarthritis?
It can be, but clicking alone does not mean you have osteoarthritis.
Osteoarthritis causes changes within a joint, including the cartilage and underlying bone. In the knee, it may lead to pain, stiffness, swelling and a grating or crackling sensation during movement.
You might notice symptoms when walking, climbing stairs, standing after sitting for a while or bending your knee.
The NHS guide to osteoarthritis explains that symptoms vary between individuals. Some people experience relatively mild symptoms, while others find that pain and stiffness affect everyday activities.
If you have persistent knee pain alongside clicking or stiffness, read our guide to knee osteoarthritis symptoms, stages and treatment options.
A healthcare professional can assess your symptoms and determine whether osteoarthritis or another condition may be responsible.
Could a torn meniscus cause clicking and locking?
Yes. A torn meniscus can cause clicking, catching, swelling and difficulty fully bending or straightening the knee.
A tear may occur when you twist your knee while playing sport or during an everyday movement. Meniscus problems can also develop gradually as the tissue changes over time.
You may notice:
- Pain around the knee joint
- Swelling that develops after an injury
- Discomfort when twisting or bending the knee
- Clicking or catching during movement
- Difficulty straightening your leg fully
- A feeling that your knee is unstable
These symptoms can overlap with those of other knee conditions. An assessment is therefore important if symptoms persist, worsen or interfere with normal activities.
You can also read the NHS guide to meniscus tears for more information about possible symptoms and when to seek medical help.
When should you seek medical advice?
Not every knee click needs investigation. However, it is important to recognise when symptoms may need prompt attention.
Seek urgent medical advice through NHS 111 if:
- Your knee suddenly locks, gives way or becomes unstable, particularly after an injury.
- You experience painful clicking.
- Your knee is very painful.
- You cannot move your knee or put weight on your leg.
- Your knee is badly swollen.
- Your knee becomes hot and red, particularly if you also have a fever or feel unwell.
If your knee has changed shape following an injury, or you have numbness or loss of feeling around the leg or foot, seek emergency assessment.
If the symptoms are less urgent but your knee pain is persistent, keeps returning or affects your daily activities, arrange an appointment with your GP or another appropriate healthcare professional.
The NHS knee pain guidance explains where to seek help based on your symptoms.
How are knee clicking and locking investigated?
The assessment depends on your symptoms, how they started and whether there are signs of an injury or an underlying joint condition.
A healthcare professional may ask when the clicking or locking occurs, whether you have experienced a recent injury and whether you have pain, swelling or difficulty walking.
They may examine your knee to assess movement, tenderness and stability.
Further investigations are not always necessary. If imaging is appropriate, an X-ray can help assess the bones and identify certain joint changes, including those associated with osteoarthritis. An X-ray does not show a meniscus tear directly, so other investigations may sometimes be considered.
If your clinician recommends an X-ray, you can find out more about the Transform Medical Private X-ray Service. Whether this or another investigation is appropriate should be determined as part of your clinical assessment.
What can you do about a clicking or locking knee?
The right approach depends on the cause.
If your knee clicks occasionally without pain or other symptoms, you may not need treatment. If it is painful, swollen or unstable, avoid activities that aggravate it until you have received appropriate advice.
For a recent minor injury, the NHS recommends resting the knee from aggravating activities and applying an ice pack wrapped in a towel for up to 20 minutes every two to three hours. Gentle movement may be appropriate as symptoms settle, but do not force a locked knee to move.
Treatment for an underlying condition may include physiotherapy, activity adjustments or medication. Some injuries and joint conditions require further specialist assessment, and surgery may be considered in selected cases.
There is no single treatment suitable for everyone. The most appropriate option depends on the cause of your symptoms, their severity and how they affect your everyday life.
Understanding what your knee is telling you
Knee clicking, popping and locking can have different explanations. Occasional painless clicking is often harmless, while symptoms such as painful clicking, true locking, swelling or repeated giving way deserve closer attention.
If your knee is persistently painful, becomes stuck or feels unstable, do not rely on the sound alone to decide what is wrong. An appropriate clinical assessment can help identify the likely cause and determine whether further investigation or treatment is needed.