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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.

By observing the variation of intradiscal pressure occurring at different body postures, it is possible to infer a functional hydrostatic behavior of a lumbar disc. Results from such observations on normal discs are already available. However, observations on degenerate discs are largely restricted to in vitro studies. The authors are now able to report a series of recordings taken from discographically degenerate lumbar discs in patients presenting with low-back pain. In this study of twenty patients, pressure observations were made on 21 normal and 19 abnormal discs. From the results that the authors have obtained, they can reaffirm that normal discs behave predictably and as previously described. The abnormal discs, however, did not behave as a single group. They showed patterns of pressure changes in different postures often dissimilar from that shown by the normal discs both in the absolute values recorded and the sequential changes that occur during the postural change. Unfortunately, the authors were unable to correlate either the extent or character of disc degeneration with the observed variation in pressure changes.