Histologic grading scale.^*

*This scale mainly scores the disruption of nucleus pulposus central cavity and cellularity, and collagen fiber orientation of annulus fibrosus. Simple radial clefting = the presence of radial gaps between AF lamellae with minimal fragmentation; complex radial clefting = presence of radial, transverse, and/or oblique gaps in the lamellae with significant fragmentation. Based on Norcross et al., 2003. Histologic grading scale.*