Figure 1

The transition from a healthy to an early degenerated intervertebral disc. Macroscopic and microscopic images showing a healthy intervertebral disc (IVD) (left), and the transition (middle) into an early degenerated IVD (right). The healthy IVD (upper left) consists of a well-distinguished lamellar annulus fibrosus (AF) and a bean-shaped nucleus pulposus (NP). During disc degeneration, the distinction between AF and NP becomes less clear (upper middle and right). In the healthy NP, notochordal cells (NCs) are the main cell type present (lower left), whereas in the transitional NP, a mixture of cartilage-like cells (CLCs) and NCs is present (lower middle). In early IVD degeneration, CLCs are the main cell type present in the NP (lower right).