Observations of pressures within normal discs in the lumbar spine.

As a result of performing pressure standardised lumbar discography, in vivo pressure measurements within lumbar discs have been recorded. Our results support the theory that for normal discs, the internal pressure within the nucleus pulposus increases when the subject changes from lying prone to standing and thence to sitting. However, when comparing our results with other published data, we consistently show a reduction in the absolute values recorded. We discuss the possible reasons for this discrepancy. Arguments have been advanced in the literature both for and against the nucleus in a normal disc behaving hydrostatically. An hypothesis which occupies the middle ground between these two concepts is proposed which could well be consistent with all the published data including our own.