INTRODUCTION: Mechanical stress is implicated in initiating and accelerating degenerative disc disease. Studies hitherto have not analyzed in‐vivo alterations in diffusion under loaded conditions and do not also reflect real life mechanical loading conditions. Scoliotic discs offer a perfect biological model of compressive and tensile stress in a young population without overlapping changes of ageing.
METHODS: 21 discs from six patients with adolescent idiopathic scoliosis (AIS) were assessed pre‐operatively by serial post contrast MRI and were then harvested during surgery for histological and biochemical evaluation. Results were compared to control discs harvested from tumor surgery and also correlated to Cobb angle, disc wedge angle, disc inclination angle, coronal migration and the level of the discs.
RESULTS: Altered diffusion patterns due to end‐plate damage (EPD) was universal with site specific breaks in two, double‐peak pattern in three, high intensity pattern in 14 and frank contrast leak in two. Cell density was lower on the convex side in both the EP and NP (P < 0.05). The percentage of viable cells was comparatively less in the concave side (P ‐ 0.000) and also significantly lower at all levels compared to normal (P ‐ 0.000). Widespread neovascularization was noted. Changes in water, lactate and glucose content were found to depend on Cobb angle and level of disc. Regression Analysis showed that truncal decompensation and Cobb angle were the primary predictors for changes in cell density, severity of matrix degeneration, calcification changes and water content.
DISCUSSION: EPD occurs early and altered nutrition may be the primary mechanism by which mechanical stress induces degeneration. Unlike previous studies, we found histopathological and biochemical alterations to be more severe in caudal discs than at apex, especially in the presence of truncal decompensation. Our findings have important implications in timing and choice of surgery in AIS.