What Makes the Cracking Sound During a Chiropractic Adjustment?

By Benjamin McCay, DC, CCSP

Published September 21, 2026

The “crack” or “pop” that sometimes occurs during a chiropractic adjustment is probably the most recognizable part of chiropractic treatment. It can also be one of the most misunderstood.

Despite how it sounds, your bones are not cracking, grinding together, or being forced back into place. The sound usually comes from a rapid pressure change within a joint—a process known as cavitation. Although many people associate a loud pop with a good adjustment, the sound itself is not what makes the treatment effective.

What Happens Inside the Joint?

Many of the joints that move freely in the body—including the small facet joints of the spine—are synovial joints. These joints are enclosed by a capsule and contain a small amount of lubricating fluid called synovial fluid, which helps the joint move smoothly.

When a joint is moved or distracted during an adjustment, the joint surfaces may separate very rapidly. This causes the pressure inside the joint to drop. Under the right conditions, gases such as carbon dioxide and nitrogen that are normally dissolved in the joint fluid can come out of solution and form a small gas-filled cavity—a process called cavitation. This happens extremely quickly and can produce the familiar cracking or popping sound. Afterward, the gas gradually dissolves back into the joint fluid as conditions return toward normal.

Is It a Gas Bubble “Popping”?

That is the common explanation, but it is probably too simple. For many years, researchers believed that the cracking sound resulted from a gas bubble forming and then collapsing inside the joint.

In 2015, researchers used real-time MRI to actually watch a finger joint while it was being cracked. They found that a cavity appeared at essentially the same time as the cracking event—and importantly, the cavity remained visible afterward. This suggested that the sound was associated with the rapid formation of the gas cavity rather than simply a bubble disappearing.

A later mathematical study showed that partial collapse or oscillation of the newly formed cavity could also generate a sound matching what is heard during joint cracking, while still leaving part of the cavity behind. So the precise acoustic mechanism is still being studied.

The important part is that the sound is associated with rapid joint separation and cavitation within the joint fluid—not bones cracking against each other.

Why Can't the Same Joint Usually Crack Again Right Away?

If you crack one of your knuckles, you may notice that you usually cannot immediately crack the same joint again. After cavitation occurs, the joint goes through a temporary refractory period during which another cavitation is unlikely to occur. The gas and pressure conditions inside the joint need time to return to their previous state.

Finger joints have shown refractory periods of roughly 20 minutes. In one small preliminary study of three subjects, audible cracking after lumbar manipulation took 40 to 95 minutes to substantially recover. This is another reason repeatedly manipulating a joint simply to produce another sound does not make much sense.

Does a Louder Crack Mean a Better Adjustment?

No. The presence, number, or loudness of the pops does not tell us how successful an adjustment was.

Studies examining spinal manipulation have generally found that patients can improve whether or not an audible pop occurs. A 2022 systematic review found no evidence that producing an audible pop during spinal manipulation resulted in better pain outcomes. An earlier study of patients with low-back pain reached a similar conclusion: patients improved after spinal manipulation whether an audible pop occurred or not.

The goal of an adjustment is therefore not to make the spine crack. More meaningful considerations include whether treatment improves motion, decreases pain or muscle guarding, and helps the patient function better.

Why Can One Adjustment Produce Several Pops?

A single spinal adjustment can sometimes produce several rapid pops rather than one. The spine contains many small synovial joints positioned close together, so when an adjustment creates motion through a region of the spine, more than one joint may cavitate.

Research recording cavitation during spinal manipulation has demonstrated that several separate pops can occur during a single thrust. In one study of lumbosacral manipulation, researchers detected an average of more than five individual popping sounds during each manipulation.

This is another reason the number of pops should not be interpreted as the number of vertebrae that were somehow “put back into place.” As discussed in our article on joint dysfunction and the “bone out of place” explanation, chiropractic adjustments are better understood in terms of movement and function than as physically relocating misplaced vertebrae.

Does Joint Cracking Cause Arthritis?

There is no good evidence that ordinary joint cracking causes osteoarthritis. This question has been studied most extensively in people who habitually crack their knuckles.

A study comparing people with and without hand osteoarthritis found no association between knuckle cracking—including how frequently or for how many years someone had cracked their knuckles—and the development of osteoarthritis. A review of the scientific literature reached a similar conclusion: observational studies have generally failed to demonstrate a relationship between habitual knuckle cracking and osteoarthritis.

However, most of this research involves the joints of the hand. It is not known whether these findings apply to habitual self-cracking of the neck, because long-term studies examining whether repeated cervical self-manipulation contributes to arthritis or other degenerative changes have not been done.

That does not mean every method of repeatedly forcing or twisting a joint is advisable. It simply means the cavitation sound itself should not be confused with joint damage.

Not Every Joint Noise Is Cavitation

Joints can make many different sounds, and not all of them are the same phenomenon. A single pop that occurs after a joint has been relatively still is often consistent with cavitation.

Repeated clicking or snapping during the same movement may instead come from a tendon or ligament moving over a bony prominence or another nearby structure. Grinding or crackling—sometimes called crepitus—can have still other causes, including irregular joint surfaces or age-related changes within the joint.

The sound therefore has to be considered along with what the joint is doing and whether symptoms such as pain, swelling, locking, or instability are present.

The Sound Isn't the Treatment

The cracking sound produced during some chiropractic adjustments is a mechanical consequence of rapid joint movement and cavitation. It is not the sound of bones breaking, and it does not mean that a vertebra was “out” and suddenly snapped back into position. An adjustment also does not necessarily need to make a noise to be effective.

A better way to judge treatment is by what happens afterward: Does the patient move better? Is there less pain or guarding? Can they return more comfortably to normal activities? Those outcomes matter considerably more than how loud the adjustment was.