What Actually Happens During a Chiropractic Adjustment (The Pop Explained).

Before a lot of people's first chiropractic visit, there's a moment of YouTube-watching where they see someone's neck get twisted and hear a loud crack and think "absolutely not." We get it. Out of context, it looks alarming.

Here's what's actually happening. The sound, while dramatic, is the least interesting part of the whole process.

The Anatomy: What Is a Spinal Joint?

Each vertebra in your spine is connected to its neighbors by several structures: the intervertebral disc in front, and two facet joints in the back. The facet joints are synovial joints, the same type as your knee or hip. They're enclosed in a joint capsule filled with synovial fluid, which lubricates the joint and allows smooth movement.

When a facet joint becomes restricted, meaning it's not moving through its full range of motion, it can create pain, limit spinal mobility, and alter the mechanics of surrounding segments. This is what chiropractors call a "subluxation" or joint fixation, and it's what an adjustment is designed to correct.

The Sound: What Is the Pop?

The prevailing explanation for decades was that the pop was caused by cavitation: the rapid formation of a gas bubble in the synovial fluid when the joint is quickly distracted. The theory: intra-articular pressure drops suddenly, dissolved gases (carbon dioxide, nitrogen, oxygen) come out of solution, and the bubble's formation creates the audible click.

Research published in the International Journal of Sports Physical Therapy examined cavitation sounds during cervicothoracic spinal manipulation and confirmed that audible pops correspond to joint manipulation events, though the exact acoustic signature varies by location and technique.¹

More recently, some researchers have challenged the original cavitation model in favor of "tribonucleation": the idea that the surfaces of the joint briefly separate rather than gas forming in the fluid itself.² The honest answer is that the exact mechanism is still being refined. What is clear is that the pop is a joint event, not a bone cracking, and not anything breaking.

The pop is also not required for a successful adjustment. Many effective techniques are completely silent.

What the Adjustment Actually Accomplishes

The mechanical goal of a high-velocity, low-amplitude adjustment is to restore normal movement to a restricted joint. But the effects go beyond the joint itself:

• Neurological input. The adjustment stimulates mechanoreceptors in the joint capsule, sending a burst of non-pain signal to the spinal cord that can interrupt or "gate" the pain signals traveling up the same pathway. This is part of why pain relief can be immediate.
• Muscle relaxation. The surrounding paraspinal muscles, which have often been guarding the restricted segment, tend to relax after the joint restores normal motion. The spasm maintaining the fixation no longer has a reason to be there.
• Restored kinematics. When one segment is fixed, adjacent segments compensate by moving more than they should. Restoring proper motion to the restricted joint reduces abnormal load on its neighbors.

Does It Actually Work?

Yes, and the research on this is solid. A systematic review and meta-analysis of 47 randomized controlled trials published in the BMJ found that spinal manipulative therapy produced statistically significant improvements in pain and function for chronic low back pain, and that the effect sizes were clinically meaningful, not just technically positive.³

The same review found that the benefit was comparable to other recommended therapies for back pain and that serious adverse events were rare.

What to Expect at Your First Visit

Before any adjusting happens, we do a full exam: range of motion, orthopedic and neurological testing, and a health history. An adjustment is never performed without a clinical reason. We identify which segments are restricted and why, and the treatment follows from that assessment.

Most people feel immediate improvement in mobility after their first adjustment. Soreness for 24–48 hours afterward, similar to post-workout soreness, is normal and temporary.

Ready to experience it for yourself? Our chiropractic adjustment page has the full breakdown of what your first visit looks like.

References

1. Dunning J, Mourad F, Zingoni A, et al. Cavitation sounds during cervicothoracic spinal manipulation. International Journal of Sports Physical Therapy. 2017;12(4):642–654. PMID: 28900571.
2. Evans DW. Why is the prevailing model of joint manipulation (still) incorrect? Chiropractic & Manual Therapies. 2022;30:51. PMID: 36494698. DOI: 10.1186/s12998-022-00460-2.
3. Rubinstein SM, de Zoete A, van Middelkoop M, et al. Benefits and harms of spinal manipulative therapy for the treatment of chronic low back pain: systematic review and meta-analysis of randomised controlled trials. BMJ. 2019;364:l689. PMID: 30867144. DOI: 10.1136/bmj.l689.