Understanding the Chiropractic “Pop” - Part 2: The physics and what happens in the joint

In Part 1, we looked at the structure of the facet joint — how it’s formed, what it does, and why it matters in spinal movement. Now, let's zoom in on a question nearly every patient asks:

"What makes that popping noise when you adjust my spine?"

Let’s break it down (without actually breaking anything).

What’s Actually Happening When You Hear That Pop?

The sound is called joint cavitation, and it’s a totally normal, safe physiological response that happens inside synovial joints (like your facet joints, finger joints, or knuckles).

Each of these joints is surrounded by a capsule filled with synovial fluid, which lubricates the joint and helps absorb shock.

When a chiropractor performs an adjustment — a fast, controlled force in a specific direction — it causes the two joint surfaces to rapidly separate by a small amount. This momentary separation creates a drop in pressure inside the joint capsule.

This change in pressure causes dissolved gases (mostly carbon dioxide) in the synovial fluid to form a gas bubble. It’s the creation of this bubble — not the bursting of it — that produces the audible pop.

The Coke Can Analogy

Think of it like opening a can of Coke. Inside the can, gas is dissolved in the liquid under pressure. The moment you open it, the pressure drops, and gas bubbles form with a fizzy pop.

Your joints work on a similar principle. They’re sealed containers. When pressure drops quickly (as during an adjustment), a gas bubble forms — and that's what you hear.