Vacuum phenomena involving the intervertebral discs are a result of accumulation of gas (principally nitrogen) with the crevices of the intervertebral discs or adjacent vertebrae.
This commonly occurs in association with intervertebral disc degenerative disease.When spinal disc or a joint degenerates (wears out) and over time, as the cartilage erodes away, some gas bubbles build up in the joint space or inside the disc.