Vascularization and Morphological Changes of the Endplate After Axial Compression and Distraction of the Intervertebral Disc

Study Design. An in vivo study of the rabbit's endplate and intervertebral disc (IVD). Objective. To assess the histologic features and vascularization of the endplate after axial compression and distraction, along with the degeneration and regeneration status of IVD. Summary of Background Data. Current studies mainly focus on the changes in the IVD in response to degener-ation and regeneration. However, the basic science regarding degenerative changes of the vertebral endplate and its actions on the IVD is lacking. The endplate is responsible for nutrient flow to the IVD through diffusion. It has been postulated that changes in the endplate may be responsible for the degeneration of the IVD. Methods. Twenty New Zealand white rabbits were equally divided into 4 groups as follows; group A, 28 days of compression only; group B, 28 days of disc compression followed by 28 days of unloading; group C, 28 days of disc compression followed by 28 days of distraction; and group D, sham operated animals with apparatus placement only. At the end of the study, all the animals in the 4 groups were killed and the lumbar segments harvested for analysis of their disc height, vascularity, and histologic examination. Results. Compression decreased the disc height and the rabbits showed signs of disc degeneration. Ossified endplates with decreased cells and extracellular matrix, and decreased vascular channel volume were observed. Cellular and morphologic regeneration were observed on unloading and distraction of the compressed discs, although the cartilaginous endplates were partially ossified. The volume of vascular channels increased significantly after distraction. Fluorescent vascular tracer showed the presence of active blood flow in the vascular channels near the cartilaginous endplates. Conclusion. Compression resulted in degeneration of the cartilaginous endplate and decrease in the osseous endplate vascular channel volume, both of which led to the degeneration of the IVD. Unloading and distraction allowed the regeneration of the extracellular matrix in both the endplate and the recovery of vascular channels.