Cervical and thoracic intervertebral disc hydration increases with recumbency: a study in 101 healthy volunteers

BACKGROUND CONTEXT: Variation in the water content and the size of lumbar intervertebral discs (IVDs) is known to occur because of recumbency and has been associated with lumbar IVD herniation risk through the impact of IVD hydration on tissue mechanical properties. It is not clear if similar changes in cervical or thoracic IVDs occur with recumbency. PURPOSE: The aim of this study was to determine whether increases in hydration of thoracic and cervical IVDs occur with short-duration recumbency. STUDY DESIGN/SETTING: This study used a test-retest design in a magnetic resonance imaging facility. METHODS: We examined expansion of all IVDs in the spine in 101 healthy individuals (54 women) aged 25-35 years on sagittal T2-weighted magnetic resonance images after a mean of 26.9 minutes lying in the scanner bore. All scans were performed after midday. To mitigate false positives, p-values were adjusted by the false discovery rate method. RESULTS: At the end of lying, the cervical spine IVD volume increased by a mean (standard deviation) of 2.6 (5.6)% (p<.001) compared with a 1.0 (4.0)% (p=.024) increase in the upper thoracic spine IVD volume and a 2.0 (3.2)% (p<.001) increase at the lower thoracic spine. Lumbar IVD volume increased by 1.2 (2.4)% (p<.001). C2-C3 IVD volume (+ 4.1 [13.8]%, p=.011) increased the most at the cervical spine, followed by C5-C6 (+ 3.9 [9.8]%, p<.001) and C3-C4 (+ 3.8 [13.5]%, p=.014). Lumbar IVDs with higher degeneration grades showed more expansion with lying (p=.0031). CONCLUSIONS: We established that cervical and thoracic IVD volumes increase with recumbency. We expect diurnal variation in cervical and thoracic IVD hydration will occur in the general population, with greater cervical and thoracic IVD hydration and size upon rising in the morning. (C) 2017 Elsevier Inc. All rights reserved.