Knee Cracking and Popping: 3 Reasons You DON’T Need Surgery

TLDR

• Most knee cracking and knee popping sounds are harmless and come from normal changes in pressure, tiny air bubbles in the synovial fluid, or natural tissue movement around the knee joint.
• These sounds are usually nothing to worry about unless they come with pain, swelling or reduced movement.
• If your knee keeps popping and hurting, it may be linked to issues like knee osteoarthritis, cartilage irritation or meniscus tears.
• A physiotherapist can assess your symptoms, provide an accurate diagnosis, and guide you with exercises for better knee health.
• For most people, noisy knees are common, safe and don’t require surgery.

Physiological vs pathological sounds

The most important difference in knee cracking or knee popping sounds is whether they are painful or non-painful. Clinically, this is described as physiological knee noise (normal, harmless) versus pathological knee noise (Song et al., 2018).

Most people experience normal physiological knee sounds, especially when the knee joint moves, bends or shifts. These are usually associated with:

• No worsening cracking sounds or increased symptoms (such as reduced range of motion, more knee pain, or decreased function)
• No history of injury
• Sporadic or inconsistent popping sounds (e.g. “Sometimes it cracks, other times it doesn’t.”)

Pathological noise, on the other hand, is often linked with more concerning symptoms, such as:

• Swelling or effusion around the knee joint
• A loud pop at the time of injury, often accompanied by pain or sharp pain
• Consistent cracking sound or grinding sensation during movement

A proper assessment is important to reach an accurate diagnosis. A physiotherapist or physical therapist can assess your knee pain or swelling, identify the underlying problem, rule out issues like a torn meniscus, and determine whether your symptoms relate to knee crepitus, patellofemoral pain syndrome, or other common causes. In many cases, a doctor’s visit or orthopedic surgery review is not required.

What causes noisy knees?

Most noisy knees happen because of completely normal mechanics inside the knee joint. When your knees crack or you notice a popping sound, it often comes from pressure changes in the synovial fluid or tiny air bubbles forming and collapsing during everyday movements like walking or knee bends. Sometimes the sound relates to how the patella moves, how the leg muscles support the joint, or mild irritation from repetitive stress – all common in younger and older people alike.

Physiological knee noise

The exact cause of harmless, physiological knee popping varies. Research suggests several possible mechanisms:

• Buildup or bursting of tiny gas bubbles in the synovial fluid
• Ligaments or tendons stretching over a bony lump and snapping back into place
• Normal catching of the synovium or physiological plica
• Hypermobile or discoid meniscus
• Post-surgical changes (Song et al., 2018)

The “bubble collapse” theory is one of the most widely accepted explanations. As the knee joint moves, tiny bubbles of air within the synovial fluid can rapidly collapse, causing that familiar popping sensation or sound. This is why the sound is often sporadic and hard to reproduce immediately after your knees crack.

Why do my knees crack so much?

If you’re wondering, “Why do my knees crack so much?” – you’re not alone. Frequent knee cracking or popping sounds are usually part of a common phenomenon where the knee joint responds to pressure, movement, and changes in the surrounding tissues. For many people, especially younger people and those who move a lot during the day, these sounds come from harmless shifts within the joint, such as collapsing gas bubbles in the synovial fluid, or tendons moving slightly as the leg muscles activate.

Your knees may also crack more often if your body weight places extra load on the joint, if you’ve recently increased your physical activity, or if your cartilage naturally thins with age. These noises are typically not a cause for concern unless they’re accompanied by pain, swelling, or reduced movement. A physical therapist can help rule out issues like runner’s knee, patellofemoral pain syndrome, or an underlying joint health imbalance if the noise is persistent or bothersome.

Pathological knee noise

There are many potential causes of pathological knee noise, including degenerative changes such as knee osteoarthritis, pathological plica, patellofemoral instability, pathological snapping knee syndrome and post-surgical crepitus (Song et al., 2018).

A physical therapist or sports medicine professional can assess your movement, check for issues such as meniscus tears or anterior cruciate ligament injuries if you also feel pain, and guide you toward better knee health with personalised knee exercises and advice.

Why does my knee keep popping and hurting?

If your knee keeps popping and hurting, this usually means the sound is no longer purely physiological and may indicate an underlying problem. While occasional popping sensations without pain are normal, popping that is accompanied by pain, swelling, or a consistent grinding sensation may be related to conditions such as knee osteoarthritis (knee OA), irritation around the cartilage, or more structural issues like meniscus tears, a torn meniscus, or even anterior cruciate ligament injuries after a specific common injury event.

Painful popping can also come from the patella not tracking smoothly, reduced blood supply to certain tissues, or excessive stress placed on the joint during sports or an intense workout. In these cases, avoiding movement or choosing to stop exercising may actually delay recovery. Instead, seeking medical attention from a physiotherapist, sports medicine physician, or orthopedic surgeon can help provide an accurate diagnosis and the right plan to support knees strong, improve knee health, and protect long-term function.

The osteoarthritic knee

Common characteristics of knee osteoarthritis can lead to knee crepitus, including gradual cartilage loss, bony spurs, and cyst formation. Crepitus in the knee is often associated with patellofemoral osteoarthritis.

Research shows that more severe osteoarthritis is strongly correlated with greater knee pain, reduced mobility and a higher likelihood of structural abnormalities such as:

• Full-thickness cartilage defects
• Synovitis
• Complex or macerated meniscus tears
• Large osteophytes

(Neogi et al., 2009; Sowers et al., 2011)

However, regular movement and knee exercises can slow progression (Bosomworth, 2009). In many cases, people who stay active experience reduced pain and improved function compared to those who stop exercising.

How do you manage knee noises and/or knee osteoarthritis?

Managing noisy knees depends on whether the noise is physiological or pathological. Often, the biggest factor influencing your experience is not the cracking sounds themselves, but how you interpret them. Worrying that something’s “wrong” with the knee joint can increase sensitivity, reduce confidence, and make people avoid movement.

Comments from friends or family such as:

• “Your knees make you sound older”
• “Your knees sound arthritic”
• “That doesn’t sound good”

…can unintentionally make this worse.

It’s important to remember:

Knee cracking is usually harmless unless it is accompanied by pain, swelling or functional changes.

If your knee keeps popping and hurting, or you’re unsure whether it’s normal or something more serious, it’s best to book a physical therapy appointment with a physiotherapist for an accurate diagnosis.

You can also check out my knee taping guide and knee pain guide if you’re experiencing discomfort around the knee.

Final thoughts

Knee noises can feel worrying when you don’t know the cause. But in most cases, knee cracking and popping sounds are simply harmless, physiological noises that occur in almost every person’s knee joints.

If your knees crack with pain, swelling or movement limitations, speak with a local health practitioner. Otherwise, keep moving – maintaining strong leg muscles and staying active gives you the best chance of maintaining joint health and slowing age-related changes like knee OA.

Do your knees crack or pop regularly? Just remember – most of the time, it’s not a cause for concern.

References

• Bosomworth N. J. (2009). Exercise and knee osteoarthritis: benefit or hazard?. Canadian family physician Medecin de famille canadien, 55(9), 871–878.
• Neogi, T., Felson, D., Niu, J., Nevitt, M., Lewis, C. E., Aliabadi, P., Sack, B., Torner, J., Bradley, L., & Zhang, Y. (2009). Association between radiographic features of knee osteoarthritis and pain: results from two cohort studies. BMJ (Clinical research ed.), 339, b2844. https://www.bmj.com/content/339/bmj.b2844
• Song, S. J., Park, C. H., Liang, H., & Kim, S. J. (2018). Noise around the knee. Clinics in Orthopedic Surgery, 10, 1 – 8.
• Sowers, M., Karvonen-Gutierrez, C. A., Jacobson, J. A., Jiang, Y., & Yosef, M. (2011). Associations of anatomical measures from MRI with radiographically defined knee osteoarthritis score, pain, and physical functioning. The Journal of bone and joint surgery. American volume, 93(3), 241–251. https://doi.org/10.2106/JBJS.I.00667