Fig. 1

a Schematic representation of typical L4–L5 hernia, with compression and possible rupture of posterior longitudinal ligament (PLL). b Human LDH fragment, obtained from patient who underwent microdiscectomy after informed consent and ethics committee approval from Centro Hospitalar São João. c Histological staining of tissue collected in (b), showing cell clusters producing proteoglycans (Alcian blue) embedded in a collagen matrix (Picrosirius red). d LDH is currently divided into four subtypes, according to MRI, as bulging disc (mildest form), protrusion, extrusion, and sequestration, the severest form of LDH. Proteoglycan-rich nucleus pulposus in center is surrounded by collagen-rich concentric rings of annulus fibrosus. Scale bars: (b) 3 cm, (c) 100 μm. Image credits: (a, d) used elements from Servier Medical Art; (b, c) unpublished