Why Does My Knee Click and Pop, and Should I Worry?
Most knee clicking is completely harmless. It is usually caused by tiny gas bubbles popping in the joint fluid, or by tendons sliding over bone. If the clicking happens without pain, swelling or locking, it rarely needs any tests. When knee popping comes with pain, or the joint feels unstable, it is worth looking into.
Key points
- Painless knee clicking is very common and usually nothing to worry about.
- The medical term for joint noise is crepitus.
- Pain, swelling or locking along with clicking may point to a cartilage or tracking problem.
- A standing, weight-bearing image can show alignment problems that lying-down scans miss.
- Most people with clicking knees need reassurance, not surgery.
What is crepitus in the knee?
Crepitus is the medical name for any grinding, cracking or popping sound that comes from a joint. In the knee it is extremely common. You might hear one loud pop when you stand up, or a quiet grinding noise as you walk down the stairs. Both can be completely normal.
Your knee joint is surrounded by a capsule filled with fluid. Small gas bubbles form naturally in this fluid. When the joint moves, the bubbles collapse and make a popping sound. This is the same thing that happens when you crack your knuckles, and it is not harmful.
Tendons and ligaments can also snap lightly over bony ridges as you bend or straighten the knee. Again, this is usually painless and nothing to worry about.
What causes knee clicking and popping sounds?
Several things can make a knee noisy. Most are harmless, but a few need attention.
Tiny bubbles in the joint fluid collapse with a pop. Painless and normal.
A tendon slides over a bony bump. You feel or hear a snap, usually without pain.
When the cartilage surface becomes rough, it can cause a grinding feeling as the knee bends. This is known as chondromalacia patella.
If the kneecap does not glide smoothly in its groove, it can click or grind. This is called patellar maltracking.
Less commonly, a loud pop during sport followed by swelling may suggest a ligament injury. A catching or locking feeling can point to a loose fragment or a meniscus tear. Both of these usually come with obvious pain and swelling.
When should you worry about a clicking knee?
Most of the time, you do not need to worry at all. A clicking knee with no pain, no swelling and full movement is very likely normal. The sounds alone are not a sign of damage.
- Clicking with no pain
- The sound comes and goes
- Full movement, no swelling
- Both knees make similar noises
- Pain along with the clicking
- Swelling after activity
- The knee locks or gives way
- A single loud pop during an injury
- Grinding that gets worse over weeks
If your knee clicks and also feels unstable, locks in one position, or is visibly swollen, it makes sense to find out why. Our guide on when to see a specialist can help you decide your next step.
Urgent note. If your knee suddenly gives way with severe pain, or you have numbness or weakness in the leg, get urgent medical help. Contact your doctor or go to the nearest emergency department.
How does standing imaging help with knee crepitus?
A standing, weight-bearing image shows your knee the way it really works, under your full body weight. This matters because alignment problems that add to noisy, uncomfortable knees can be invisible when you lie down for a standard scan.
When you stand, gravity loads the joint and your muscles hold everything in its natural position. An EOS scan captures the whole leg, from hip to ankle, in one image. This shows how the kneecap tracks, whether the leg is straight or angled, and how the hip and ankle alignment above and below may be affecting the knee.
Lying on a table relaxes the muscles and takes the load off the joint. The kneecap sits differently, and small alignment shifts that cause clicking under weight disappear. A standard X-ray or CT taken lying down may show nothing wrong, even when there is a real tracking or alignment problem.
Your body works as a connected chain. A slight twist at the hip or a flat arch in the foot can change how the kneecap sits in its groove. Pain, or noise, often shows up away from the real cause. A whole-body standing image at ScanAlign can map this chain in one visit, using about 90% less radiation than a standard X-ray, around ten times less.
When MRI is the better choice. EOS shows bones, joints and alignment. If your clinician suspects a meniscus tear, ligament damage or another soft-tissue problem, MRI is usually the better tool. The two work together, they do not compete.
What helps reduce knee clicking?
For painless clicking, no treatment is needed. The noise itself is not causing harm. If the clicking is linked to discomfort, clinicians often recommend a few general approaches.
- Strengthening exercises. Building the muscles around the knee, especially the quadriceps, helps the kneecap track more smoothly.
- Changing your activity. Cutting down on deep squats or heavy loaded knee bends can ease grinding feelings while you work on strength.
- Understanding alignment. If there is an underlying alignment or tracking problem, finding it with proper imaging helps a physiotherapist or surgeon plan the right approach.
ScanAlign is a diagnostic imaging clinic. We do not provide treatment, but we give you and your clinician the detailed alignment picture that helps guide the right plan.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
If your knee clicking comes with pain, swelling or a feeling of instability, a free video consultation from home can help you understand whether a scan in London is the right next step.
Book a free video consultationFrequently asked questions about knee clicking
Yes. Most adults have some knee clicking or popping, especially when getting up from a chair, squatting or using the stairs. If there is no pain and the joint moves freely, the sound is almost always harmless.
Crepitus can feel like a light crackling under the kneecap or a deeper grinding feeling as the knee bends. Some people hear it, others just feel it. It can be barely noticeable or quite loud, but loudness alone does not show how serious it is.
Not usually. If the clicking is painless, carrying on with exercise is generally fine and even helpful. Strengthening the muscles around the knee often reduces noisy joints over time. If the clicking comes with pain or swelling, speak with a clinician before pushing through.
It can be, but clicking alone is not enough to diagnose arthritis. Many people with noisy knees have no arthritis at all. If the grinding is getting worse, or if you have stiffness and aching along with the noise, imaging can help make clear what is happening inside the joint.
Clicking is a noise or feeling during movement. Locking means the knee gets stuck in one position and you cannot straighten or bend it fully. Locking is more concerning and may suggest a loose body or meniscus tear that needs investigation.
When you bend your knee, pressure changes inside the joint cause gas bubbles to form and then pop. Tendons can also flick over bony ridges as the knee bends. Both make a crack you can hear. It sounds alarming but is usually normal.
No referral is needed. ScanAlign is a private, self-pay clinic. You can book a knee assessment directly. The process starts with a free video consultation to check that imaging is suitable for your situation.
Yes. An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less. It takes the image while you stand, with no need for contrast dye or injections.
The price for patients travelling from abroad is confirmed during the free video consultation. There is no obligation to book a scan afterwards.
Yes. If the leg is slightly rotated or angled, the kneecap may not sit in the centre of its groove. This can cause clicking, grinding or discomfort, particularly under load. A standing, whole-body image can show whether alignment higher up at the hip or lower down at the ankle is playing a part.
Still unsure about your clicking knee?
A free video consultation, from wherever you are, helps you understand whether imaging would add useful information. There is no pressure and no obligation.
Book a free video consultationSources
- Song SJ, Park CH, Liang H, Kim SJ. Noise around the knee. Clinics in Orthopedic Surgery. 2018;10(1):1-8.
- NHS. Knee pain and clicking. nhs.uk. Accessed 2025.
- de Oliveira Silva D, Barton CJ, Crossley KM, et al. Implications of patellofemoral crepitus for diagnosis and management. British Journal of Sports Medicine. 2018;52(22):1445-1446.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.