What is the cracking noise with an adjustment and is it safe?

Chiropractic adjustments most commonly elicit an audible “pop” or “crack” sound. Chiropractors refer to this as an “audible release” or “cavitation sound.” Treatment success is not dependent upon this noise. Your spinal joints contain a fluid known as synovium. The synovial fluid contains dissolved gasses; mostly carbon dioxide. When your spine is adjusted, a vacuum is created within the joint and the dissolved gasses come out of solution, forming a gas bubble. This vacuum creates a “pop.”