In 1942 Knutsson correlated vacuum phenomenon (VP) with disc degeneration. In current radiological practice, the general and universally accepted term “vacuum phenomenon” is incorrectly used to characterize gas-like density that can either be due to true VP caused by a rapid increase in the volume of joint space (“acute VP” as seen in the protraction of the shoulder in children) or represent a true gas as commonly seen in degenerative disc of the spine, called “subacute” or “chronic VP”.
These lucent areas are produced by gas, mainly nitrogen, accumulating in the clefts and are accentuated on radiography obtained during extension of the spine. Vacuum phenomena are a reliable indicator of disk degeneration, and their visualization virtually excludes the presence of tumor or infection.
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| Vacuum phenomenon. Gas collects in the disk clefts and radiolucent areas appear (red arrows). |
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