Staying connected: structural integration at the intervertebral disc–vertebra interface of human lumbar spines

Abstract

Purpose:To investigate the microscopic fibrous integration between the intervertebral disc, cartilage endplates and vertebral endplates in human lumbar spines of varying degrees of degeneration using differential interference contrast (DIC) optics. Weakness at these junctions is considered to be an important factor in the aetiology of disc herniations. Methods:Magnetic resonance images (MRIs) of cadaveric lumbar spines were graded for degeneration and motion segments from a range of degenerative grades isolated and bisected sagittally. Following fixation and decalcification, these were cut into segments containing anterior or posterior annulus fibrosus or nucleus pulposus. The segments were cryo-sectioned and sections visualised using both standard light and DIC microscopy. Results:Detachment at the interface between the disc and vertebrae increased with greater degenerative grade (from 1.9% in Grade I to 28% in Grade V), especially at the boundary between the cartilage and vertebral endplates. DIC microscopy revealed the fibrous organisation at the IVD-cartilage endplate interface with structural features, such as annular lamellae branching and nodal insertions in the nucleus pulposus region; these have been previously observed in ovine spines, but were less uniform in humans.Structural integrity of the IVD and cartilage endplate was also lost with increasing degeneration. Conclusions:This preliminary study shows that microscopic structural features may act to maintain attachment between the IVD and CEP in the human spine. Loss of structural integrity in this region may destabilise the spine, possibly altering the mechanical environment of the cells in the disc and so potentially contribute to the aetiopathogenesis of IVD degeneration.

Structure‐function relationships at the human spinal disc‐vertebra interface

“…Our findings indicate that the CEP and vertebra at the inner annulus region are not well-integrated, which is supportive of previous findings [24][25][26] and may explain the weakness of this zone. Because the CEP and inner annulus are structurally integrated, tension at the CEP-bone interface generated during certain spinal movements can avulse the cartilage from the underlying bone ( Fig.…”

How maturity influences annulus‐endplate integration in the ovine intervertebral disc: a micro‐ and ultra‐structural study

“…() and Brown et al. () have demonstrated at the microscopic level a similar mode of anchorage in mature human lumbar discs. Rodrigues et al.…”

“…These authors proposed that this branching morphology serves to strengthen the anchorage by increasing the interface area over which shear forces are distributed (Rodrigues et al 2012). More recently, both Liu et al (2015) and Brown et al (2016) have demonstrated at the microscopic level a similar mode of anchorage in mature human lumbar discs. Rodrigues et al (2015) also conducted a fibril-level structural analysis and provided evidence of short range integration between the branched annular sub-bundles and the cartilaginous and vertebral endplate fibrils (Rodrigues et al 2015).…”

Tidemark Avulsions are a Predominant Form of Endplate Irregularity

“…While rim lesions are well-documented, 15,16 the precise failure location of annulus fibers along the tidemark has only been described in biomechanical studies of excised animal tissue 7 and has not been previously described in human spines. Several prior studies have described the tidemark in human spines, 17,18 which is also an important feature of tendon-bone insertions 19 and articular cartilage-bone interfaces. 20 Around the periphery of the disc, the cartilage endplate is calcified throughout its entire thickness, and the tidemark lies between the annulus and this calcified cartilage.…”