Characterization of bone & cartilage endplate junction in the human lumbar spine: novel ultrastructural insights & association with elemental composition, vascularity and degeneration.

Abstract

Intervertebral disc (IVD)-related pathology is associated with integrity of cartilaginous endplate (CEP), bony endplate (BEP) and their junction. However, ultrastructural details of the CEP, BEP and IVD and their interplay with disc degenerative features such as fissures and calcification are understudied. The current study aimed to ultra structurally explore CEP-BEP junction to IVD features. Fifty-nine lumbar motion segments from 13 male human cadavers (range, 21-80 years of age) were analyzed macroscopically, histologically and through scanning electron microscope. The fissures present in CEP & IVD and gaps at the junction of CEP-BEP & CEP-IVD were measured and correlated with calcification, vascular channels and disc degeneration. Energy-dispersive X-ray analysis (EDX) provided the elemental composition of the CEP, BEP and IVD. Ultrastructural analysis revealed gaps at the CEP-BEP junction which were occasionally bridged by fine fibrillar adhesions. These junctional gap-width were in significant positive correlation with age (p = 0.001), spinal-level (p = 0.01), severity of disc degeneration (p < 0.001) and IVD calcification (p < 0.001). The vascular channels of BEP around the CEP were in significant positive correlation with age (p = 0.003), junctional gap-width (p < 0.001) & severity of disc degeneration (p < 0.001). EDX distribution of calcium in CEP was also associated significantly with junctional gap-width & vascularity (p = 0.03, p = 0.04, respectively). This is the first study to ultrastructurally assess and map lumbar CEP, BEP and IVD in humans, noting discovery of specific phenotypic patterns of intradiscal calcification, fissures, vascularity and degeneration severity as associated with novel anatomical structures of "adhesion bridges and gaps" which are implicated in marked inflammation and pain.