Low rate loading-induced convection enhances net transport into the intervertebral disc in vivo

Abstract Background context The intervertebral disc primarily relies on trans-endplate diffusion for the uptake of nutrients and the clearance of byproducts. In degenerative discs, diffusion is often diminished by endplate sclerosis and reduced proteoglycan content. Mechanical loading-induced convec...

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Bibliographic Details
Published in:The spine journal 2015-05, Vol.15 (5), p.1028-1033
Main Authors: Gullbrand, Sarah E., PhD, Peterson, Joshua, BS, Mastropolo, Rosemarie, BS, Roberts, Timothy T., MD, Lawrence, James P., MD, MBA, Glennon, Joseph C., VMD, DiRisio, Darryl J., MD, Ledet, Eric H., PhD
Format: Article
Language:English
Subjects:
Animals
Cartilage endplates
Contrast Media - administration & dosage
Contrast Media - pharmacokinetics
Convection
Disc nutrition
Gadolinium DTPA - administration & dosage
Gadolinium DTPA - pharmacokinetics
Intervertebral disc
Intervertebral Disc - drug effects
Low rate mechanical loading
Nucleus pulposus
Orthopedics
Rabbits
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Summary:Abstract Background context The intervertebral disc primarily relies on trans-endplate diffusion for the uptake of nutrients and the clearance of byproducts. In degenerative discs, diffusion is often diminished by endplate sclerosis and reduced proteoglycan content. Mechanical loading-induced convection has the potential to augment diffusion and enhance net transport into the disc. The ability of convection to augment disc transport is controversial and has not been demonstrated in vivo. Purpose To determine if loading-induced convection can enhance small molecule transport into the intervertebral disc in vivo. Study design Net transport was quantified via postcontrast enhanced magnetic resonance imaging (MRI) into the discs of the New Zealand white rabbit lumbar spine subjected to in vivo cyclic low rate loading. Methods Animals were administered the MRI contrast agent gadodiamide intravenously and subjected to in vivo low rate loading (0.5 Hz, 200 N) via a custom external loading apparatus for either 2.5, 5, 10, 15, or 20 minutes. Animals were then euthanized and the lumbar spines imaged using postcontrast enhanced MRI. The T1 constants in the nucleus, annulus, and cartilage endplates were quantified as a measure of gadodiamide transport into the loaded discs compared with the adjacent unloaded discs. Microcomputed tomography was used to quantify subchondral bone density. Results Low rate loading caused the rapid uptake and clearance of gadodiamide in the nucleus compared with unloaded discs, which exhibited a slower rate of uptake. Relative to unloaded discs, low rate loading caused a maximum increase in transport into the nucleus of 16.8% after 5 minutes of loading. Low rate loading increased the concentration of gadodiamide in the cartilage endplates at each time point compared with unloaded levels. Conclusions Results from this study indicate that forced convection accelerated small molecule uptake and clearance in the disc induced by low rate mechanical loading. Low rate loading may, therefore, be therapeutic to the disc as it may enhance the nutrient uptake and waste product clearance.
ISSN:1529-9430
1878-1632
DOI:10.1016/j.spinee.2014.12.003