Fig. 4

Histology sections of explanted cervical segments (×2 magnification). a Healthy discs. Top Picrosirius red stain (stains for collagen), bottom Safranin-O stain (stains for proteoglycans). Both discs show a well organized AF composed of lamellar aligned collagen fibers which stain intense for Picrosirius red. There is a clear border to the NP which appears as a homogenous structure. It stains with Safranin-O indicating proteoglycan rich matrix. The cartilaginous endplate (black arrow) forms a border between the NP to the endplate bone (EPB). It stains intensively with Safranin-O indicating high proteoglycan content. b Discectomy discs. Top Picrosirius red, bottom Safranin-O stain. The annulus is disrupted and disorganized on both sides. Annular Picrosirius red staining is less intense. There is no NP tissue left in the disc space (DS). The cartilaginous endplate completely disappeared. The Endplate bone is sclerotic indicated by dense cortical bone structure and decreased trabecular bone. The collapse of the disc space is visible on histological sections