Intervertebral disc nutrition. Diffusion versus convection.

Nutrient diffusion across the vertebral endplate can occur by convection (bulk flow) or diffusion. Previous studies, using animal models, suggested diffusion as the primary mechanism of small-solute transport but did not adequately determine the contribution of bulk flow to total nutrient transport. This study was designed to reevaluate disc nutrition across the endplate. Ten microcuries of radioactive sulphate in aqueous solution were injected into L4 vertebral bodies of 13 rabbit spines following sacrifice. One hour of continuous passive flexion/extension in a physiologic range of motion was performed on five spines, while eight spines served as motionless controls. Autoradiographic techniques were used to analyze and compare the isotope uptake in the L4-L5 disc. There was no significant difference in disc uptake or the ratio of disc/bone uptake between the two groups. Motion does not significantly facilitate the transport of small solutes into the disc during short periods of time.