Pathophysiology and current understanding of degenerative disc disease

Table 1 Summary of normal anatomy and physiology of intervertebral disc

Component	Structure	Primary function	Key features
AF	Concentric collagen lamellae; outer AF rich in type I collagen, inner AF rich in type II	Resists tensile/shear forces; contains NP	Limited vascularity; provides circumferential strength
NP	Hydrated, proteoglycan-rich gel (high aggrecan/GAG content)	Generates hydrostatic pressure; absorbs compressive loads	Completely avascular; maintains hydration-dependent load distribution
CEPs	Thin hyaline cartilage layers between disc and vertebrae	Nutrient and metabolite diffusion	Primary route of nutrient/waste exchange via subchondral capillaries
Vascular supply	NP and inner AF avascular; CEP-adjacent capillary network	Diffusion-based nutrient support	Low metabolic turnover; vulnerable to hypoxia and nutrient limitation
Cellular activity	Sparse disc cells regulating ECM turnover	Maintains ECM integrity and hydration	Low metabolic reserve; sensitive to mechanical and metabolic stress
Biomechanical function	Integrated AF-NP-CEP system	Distributes compressive, tensile, and shear forces	Depends on hydration, ECM turnover, and cell viability
Vulnerabilities	Avascular, hypoxic microenvironment	Predisposed to degeneration if homeostasis fails	Risk increases with aging, mechanical load, and metabolic stress

AF: Annulus fibrosus; NP: Nucleus pulposus; CEP: Terminal endplate; GAG: Glycosaminoglycans; ECM: Extracellular matrix.