What Is That Cracking Sound?

It is probably the most common question I get asked. Someone is lying on the table, I apply a controlled thrust to their spine, and there is an audible pop or crack. Their eyes widen. "What was that?"

It is a fair question — and the answer is less dramatic than it sounds.

What actually causes the sound

Your joints are surrounded by a capsule filled with synovial fluid, which acts as a lubricant. When a joint is moved through its range quickly — as happens during a manual adjustment — the pressure inside the joint drops momentarily. This pressure change causes dissolved gases in the synovial fluid to form a bubble, which then collapses. That collapse is the popping sound you hear.

Researchers call this process tribonucleation. A 2015 study by Kawchuk and colleagues, published in PLoS One, used real-time MRI to observe this happening in finger joints. They confirmed that the sound corresponds to a gas bubble forming within the joint space — not to anything breaking, grinding, or snapping into position.

It is the same mechanism behind cracking your knuckles. The sound can seem loud when it happens in your spine, but the process is the same.

What the sound is not

There are some persistent myths about this sound that are worth addressing directly:

• It is not bones cracking. The sound has nothing to do with bone surfaces contacting each other.
• It is not bones being "put back in place." Joints do not slip in and out of position in the way that phrase implies. The idea of a bone being out of alignment and needing to be pushed back is a significant oversimplification of what is actually happening.
• It is not "correcting subluxations" in the traditional sense. While the term subluxation has a specific meaning within parts of the chiropractic profession, it does not accurately describe a bone that has moved out of place. What we are actually doing with an adjustment is influencing joint mobility, nervous system input, and the muscles surrounding the joint.

These distinctions matter because the outdated explanations can make the whole process sound more alarming — and more mysterious — than it needs to be.

Does the sound mean the treatment worked?

Not necessarily. The therapeutic value of an adjustment comes from restoring joint mobility and influencing how the nervous system and surrounding muscles respond — not from the sound itself. Some adjustments produce a loud pop. Others produce nothing at all. Both can be equally effective.

If you have ever had an adjustment that did not produce a sound and still felt better afterward, that is a good example of why the noise is not the point.

Is the sound necessary?

No. There are many effective chiropractic and manual therapy techniques that produce no sound whatsoever. Mobilisation involves slower, lower-force movements within the joint's range. Drop-piece techniques use a segmented table that absorbs the force. Sacro-occipital technique (SOT) uses the body's own weight and gravity. All of these can achieve meaningful changes in joint function without any audible pop.

In my practice, I use a range of approaches. Some involve the traditional thrust that may produce a sound. Others are quieter. The choice depends on what is most appropriate for you, your body, and your preference. If the cracking sound makes you uncomfortable, there are always alternatives — and they are not a lesser form of treatment.

Common concerns

"Will it hurt?" Most people find the adjustment itself painless, and many describe the sensation as a feeling of release or relief. You may experience some mild soreness afterward, similar to what you might feel after exercise, but this typically settles within a day.

"Is something breaking?" No. As described above, the sound is gas moving within fluid. Nothing is breaking, tearing, or being forced.

"Why does it feel good?" That is an interesting question. The current thinking is that the rapid stretch of the joint capsule stimulates mechanoreceptors — sensory nerve endings that respond to movement and pressure. This may trigger a brief relaxation response in the surrounding muscles. Some people also find the sound itself psychologically reassuring, as a kind of confirmation that something has happened.

Is it safe?

When performed by a registered, trained practitioner, spinal manipulation is considered a safe intervention. Like any manual therapy, it carries a small risk of minor side effects — temporary soreness, stiffness, or fatigue — which are generally short-lived. Serious adverse events are rare. Part of what we do at every appointment is assess whether a particular technique is appropriate for you on that day.

If you have questions or concerns about any aspect of your treatment, you are always welcome to raise them. There is no such thing as a silly question in the clinic.