That satisfying CRACK from your knuckles.
The quiet click from your knee when you stand up.
The crunching sound in your neck when you turn your head.
Our bodies are a symphony of strange and sometimes concerning sounds. It’s easy to wonder what they all mean.
Are they a sign of aging? The beginning of arthritis? Or just harmless noise?
If you’ve ever asked yourself, “why do my joints crack?” you are not alone. It’s one of the most common questions we hear as physiotherapists.
Let’s decode the messages your joints are sending you.
This guide will help you understand the difference between a harmless pop, a common click, and a grind that might need a little more attention. Most of the time, you’ll find it’s perfectly normal.
The Main Event: That Loud “POP” (Spoiler: It’s Just Gas!)
Let’s start with the most famous joint sound of all: the classic knuckle crack.
The sound can be so sharp and loud that people around you cringe, imagining your bones are breaking.
But the reality is much less dramatic and far more fascinating.
The sound comes from a phenomenon called cavitation.
Think of your joint as a tiny hydraulic system. The space between your bones is sealed by a capsule filled with synovial fluid. This fluid acts as a lubricant, like oil in an engine, and it’s full of dissolved gases—mostly nitrogen.
When you stretch or pull the joint, like when you bend your knuckle backward, you expand the volume of that joint capsule.
This decreases the pressure on the fluid inside.
Just like opening a can of soda, the sudden drop in pressure allows the dissolved gases to rapidly form a tiny bubble.
The loud “POP” you hear is the sound of that gas bubble collapsing almost as quickly as it formed.
It’s a gas bubble bursting, not your bones grinding or your cartilage shattering!
This is also why you can’t crack the same knuckle again right away. You have to wait for the gases to re-dissolve back into the synovial fluid, which can take about 20 minutes.
Myth vs. Fact: The Age-Old Arthritis Question
This brings us to the biggest myth in joint health, a warning you’ve probably heard a thousand times.
Myth: “Stop that! Cracking your knuckles will give you arthritis.”
Fact: False! This is perhaps one of the most thoroughly debunked medical myths out there.
Decades of research have found no link between the habit of knuckle cracking and the development of osteoarthritis.
The most famous piece of evidence comes from a curious doctor named Donald Unger.
For 60 years, he diligently cracked the knuckles on his left hand at least twice a day.
He left his right hand alone as the control group.
After more than 21,900 cracks, he concluded his grand experiment. The result? There was no arthritis in either hand. His work even won him an Ig Nobel Prize for medicine.
So, if you enjoy that pop, you can rest easy knowing you’re not damaging your joints. The only real harm might be annoying the people sitting next to you.
Your Joint Sound Decoder: Clicks, Snaps, and Grinds
While the dramatic “pop” gets all the attention, our joints make a whole host of other, more subtle sounds.
This is where listening to your body becomes a useful skill. Not all sounds are created equal. Let’s break down what they mean.
The “Click” or “Snap”
You stand up from your chair, and your knee clicks. You lift your arm, and you feel a “shoulder popping with movement”.
This sound is usually quick, painless, and often happens in the same spot.
What it is: This clicking or snapping sound is typically caused by a tendon or ligament moving across a bony structure.
As you move, a tight tendon might get momentarily caught on a piece of bone. When it slides back into place, it makes a “snap” — much like a guitar string being plucked.
This is extremely common in the knees, ankles, hips, and shoulders. Your anatomy, muscle tightness, and movement patterns can all influence how often it happens.
A “knee clicks when squatting,” for instance, might just be your patellar tendon gliding over the edge of your femur.
When it’s OK: If the click is painless, inconsistent, and doesn’t limit your movement, it’s almost always harmless. It’s just a quirk of your body’s mechanics.
When it’s a Warning Sign: If the click is suddenly accompanied by a sharp pain or a feeling of the joint “catching” or “locking,” it could indicate an issue like a cartilage tear (meniscus tear in the knee, for example). In this case, it’s worth getting checked out.
The “Grind” or “Crunch” (Crepitus)
This sound is often the most worrying for people.
It’s less of a sharp pop and more of a gritty, grinding, or “sandpapery” sensation. You might hear a “neck cracking sound” that feels like crunching when you turn your head.
This phenomenon has a medical name: crepitus.
What it is: Crepitus is the sound of surfaces rubbing together. In joints, this is typically the sound of cartilage—the smooth, white tissue that caps the ends of your bones—rubbing against another surface.
As we age, it’s completely normal for the perfectly smooth surface of our cartilage to become a little rougher. Think of it like a new car tire versus one that’s been on the road for 50,000 miles. It still works, but the tread isn’t as pristine.
When it’s OK: Soft, gentle crepitus without any pain is very common and generally not a cause for concern. Many people have noisy knees that function perfectly well. It’s often just a sign of normal, age-related changes in the joint surfaces. It doesn’t automatically mean you have or will get arthritis.
When it’s a Warning Sign: This is the most important distinction. When the grinding is loud, coarse, and accompanied by pain, swelling, or stiffness, it’s a signal from your body that needs attention. Painful crepitus can be a sign of osteoarthritis, where the cartilage has worn down significantly, leading to bone-on-bone friction.
Actionable Checklist: When a Pop Becomes a Problem
So, how do you know for sure when a noisy joint is just being noisy versus when it’s trying to tell you something is wrong?
Most “harmless joint popping” is exactly that—harmless. The noise itself is rarely the problem.
The problem is when the noise comes with other symptoms.
Here is your simple red flag checklist. If your joint noise is combined with any of the following, it’s time to stop guessing and seek professional advice from a physiotherapist.
1. Pain is the #1 Indicator. This is the golden rule. Harmless cracks, pops, and clicks do not hurt. If a sound is consistently accompanied by a sharp, dull, or aching pain, the joint is telling you it’s unhappy.
2. You See Swelling. Swelling is a visual sign of inflammation. It means your body is responding to an injury or irritation within the joint. A pop followed by swelling is a clear sign that something is wrong.
3. The Joint Locks, Catches, or Gives Way. Do you ever feel like your knee “locks up” and you have to wiggle it to get it moving again? Or does it suddenly buckle and feel like it can’t support you? These are signs of mechanical issues, possibly related to loose cartilage or ligament instability.
4. You’ve Lost Range of Motion. If you notice you can’t bend or straighten the joint as far as you used to, it’s a red flag. For example, you can no longer fully straighten your knee or lift your arm all the way up. This indicates a problem that goes beyond simple noise.
5. It Started After a Specific Injury. A new, persistent sound that appears after a fall, a sports injury, or an accident should always be evaluated. The trauma may have caused structural damage that needs to be addressed.
Your Body is Talking. Are You Listening?
Most of the sounds your joints make are just your body’s normal acoustics. They are part of the experience of living in a dynamic, moving machine.
The key is to learn how to listen—not just for the noise, but for the other messages that come with it.
Being in tune with your body’s sounds is a great skill. Now you know how to tell the difference between a harmless pop and a conversation worth having with a professional.
Don’t let fear or uncertainty about a noisy joint keep you from moving. Movement is life, and understanding your body is the first step to moving with confidence for years to come.
Your Next Step
If your joint sounds are accompanied by any of the red flags we mentioned—pain, swelling, locking, or stiffness—don’t guess what it means. Let our experts at physiogain.com translate the message for you. We can create a personalized plan to address the root cause, strengthen your joints, and get you moving smoothly and silently.
Book your appointment today and give your joints the expert attention they deserve!