Abstract
Introduction
Herniated disc tissue removed at surgery is mostly nucleus pulposus, with varying proportions of annulus fibrosus, cartilage endplate, and bone. Herniated nucleus swells and loses proteoglycans, and herniated annulus is invaded by blood vessels and inflammatory cells. However, little is known about the significance of endplate cartilage and bone within a herniation.
Methods
Herniated tissue was removed surgically from 21 patients (10 with sciatica, 11 without). 5-μm sections were examined using H&E, Toluidine blue, Giemsa, and Masson-trichrome stains. Each tissue type in each specimen was scored for tears/fissures, neovascularisation, proteoglycan loss, cell clustering, and inflammatory cell invasion. Proportions of each tissue type were quantified using image analysis software.
Results
Herniations from patients with sciatica had greater nerve and blood vessel invasion (P<0.05), and a greater proportion contained cartilage endplate (7/10 vs 3/11, p<0.05). Cartilage fragments were generally small (5–20% of herniated mass) and showed little swelling or proteoglycan loss, or inflammatory cell invasion, although chondrocytes often formed small clusters. Most cartilage endplate fragments had a straight edge where it had been stripped from bone. Two cartilage fragments showed some bone still attached, and three showed small defects that were filled with nucleus tissue, bone, or endothelial cells.
Conclusion
More than 50% of disc herniations contained cartilage endplate. The relatively stable nature of cartilage fragments may explain why they are less likely to resorb, and therefore more likely to cause persisting sciatica. Loss of cartilage will increase endplate permeability, increasing the risk of Modic changes, and disc infection.
