Morphology of the human vertebral endplate

It is presumed that poor intervertebral disc cell nutrition is a contributing factor in degeneration, and is exacerbated by vertebral endplate sclerosis. Yet, quantitative relationships between endplate morphology and degeneration are unavailable. We investigated how endplate bone microstructure relates to indices of disc degeneration, such as morphologic grade, proteoglycan content, and cell density. Intervertebral core samples [n = 96, 14 subjects, L1-L5 level, ages 35-85 (64 ± 16 years), degeneration grade 1 (n = 4), grade 2 (n = 32), grade 3 (n = 44), grade 4 (n = 10), grade 5 (n = 6)] that included subchondral bone, cartilage endplate, and adjacent nucleus were harvested from human cadaveric lumbar spines. The morphology of the vertebral endplate was analyzed using µCT and the adjacent nucleus tissue was collected for biochemical and cellular analyses. Relationships between vertebral endplate morphology and adjacent disc degeneration were analyzed. Contrary to the prevailing notion, vertebral endplate porosity increased between 50% and 130% and trabecular thickness decreased by between 20% and 50% with advancing disc degeneration (p < 0.05). We also observed that nucleus cell density increased (R(2)  = 0.33, p < 0.05) and proteoglycan content decreased (R(2)  = 0.47, p < 0.05) as the endplate became more porous. Our data suggest that endplate sclerosis is not a fundamental factor contributing to disc degeneration. Rather, the opposite was observed in our samples, as the endplate became progressively more porous with age and degeneration. Since ischemic disc cell behavior is commonly associated with degenerative change, this may be related to other factors such as the quality of vertebral capillaries, as opposed to decreased permeability of intervening tissues.

Mechanical profiling of intervertebral discs

Despite recent advances in imaging diagnostic technology and additional treatment options our ability to prevent or inhibit discogenic back pain has not drastically improved. The challenge of linking early degenerative patterns to dysfunction and pain remains. Using a novel material testing device designated the tissue diagnostic instrument (TDI) we measured the local stiffness and strain energy absorption in the radial direction of 13 intact intervertebral discs; effectively generating a mechanical profile of each disc. Prior to measuring mechanical properties, an MR image was taken of each spine segment and the discs were radiologically scored according to the Pfirrmann scale. After testing, a sagittal portion of each L1-L2 disc was excised from each of four spines for histology. No significant correlations were found between Pfirrmann grade and mechanical data. However, polarized light microscopy images of disc sections indicated correlations between local tissue modulus measured with the TDI and the clarity and density of lamellar striations.

Stab incision for inducing intervertebral disc degeneration in the rat

STUDY DESIGN

The degenerative response of rat tail and lumbar intervertebral discs to a stab incision was evaluated.

OBJECTIVE

To examine and compare the postinjury degenerative response of lumbar and tail discs.

SUMMARY OF BACKGROUND DATA

Although successful in larger animals, a stab incision for inducing disc degeneration in rats has not been evaluated. Rodents are desirable models for disc repair studies due to their low cost, ease of care, and fast healing times.

METHODS

Lumbar and tail discs were exposed surgically and stabbed with a number 11 blade. Disc architecture, levels of IL-1beta, IL-6, and TNF-alpha, and biomechanical properties were analyzed. A functional disability secondary to multilevel lumbar disc injury was quantified and compared with that of rats undergoing sham surgery.

RESULTS

Histologic evaluation of stabbed tail discs demonstrated a nucleus pulposus size decrease, anular collagen layer disorganization, and cellular metaplasia of anular fibroblasts to chondrocyte-appearing cells. Besides the continued presence of the stab injury tract, few changes were observed in the lumbar disc histology. Cytokine measurements indicated a transient peak in IL-1beta in tail discs 4 days following injury. No significant changes in IL-1beta, IL-6, or TNF-alpha were measured. No significant differences in biomechanical properties were observed between stab injury and sham surgery discs. Yet, despite insignificant differences in histologic, cytochemical, or biomechanical properties in the lumbar discs, the rats with lumbar stab injury had a significant decrease in walking ability 28 days after surgery.

CONCLUSIONS

Tail disc stab injury was successful in creating morphologic signs of degeneration and transient high concentrations of IL-1beta. However, the degenerative response in the lumbar discs was much slower, suggesting that site-specific factors, such as increased stability due to posterior elements and torso musculature, helped facilitate healing. Yet, functional assessment indicated that the rats were partially disabled by multiple lumbar injuries.