Abstract:
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Purpose: Circadian variation in human stature has been recognized since 1726.Diurnal height changes result from gravitational forces and are believed to result from changes in the intervertebral disc. With the availability of an MRI scanner which is capable of imaging in the erect as well as supine positions, it is now possible to study alterations in the appearances of the upright spine for the first time. This study measures disc height changes between morning and evening in both the erect and supine positions.
Methods and Materials: 32 male volunteers with no history of either low back pain or sciatica were studied using a 0.6Tesla indominitable pMRI scanner (FONAR). Each indiviual was examined supine and erect within 30 minutes of rising in the morning and again between eight and 9 hours later at the end of a normal working day. Each of the five intervertebral discs were measured using (a+p)/2, where a = anterior and p = posterior disc height. Measurements and interobserver reproducibility were performed independently by a radiolgist and an orthopaedic surgeon. Measurement results were analysed with one way ANOVA and multiple comparison post tests.
Results: The cumulative loss of lumbar disc height for the five discs was between 7.70 - 8.09mm in the erect position and between 7.29 - 7.52mm in the supine position.
Conclusion: The length of the lumbar spine is about one third of the total body height and the intervertebral discs provide about 25% of this length. This study is unique in that it allows the spine to be assessed in the erect "naturally loaded" position. Given that the observed normal diurnal loss of height has been shown to be 17.00mm, one would expect that the loss over the lumbar region to be 8.5mm. The difference between this expected loss and our findings is accounted for by the alteration in lumbar lordosis between the erect and supine positions.
Smith MD, F,
Measurement of Diurnal Variation in Intervertebral Disc Height in Normal Individuals: A Study Comparing Supine with Erect MRI. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3103199.html
