Influence of asymmetric tether on the macroscopic permeability of the vertebral end plate

The influence of artificial nucleus pulposus replacement on stress distribution in the cartilaginous endplate in a 3-dimensional finite element model of the lumbar intervertebral disc

OBJECTIVE

This study aimed to investigate the effects involved with the artificial nucleus pulposus (NP) replacement on stress distribution of the cartilaginous endplate (CEP) in a 3-dimensional lumbar intervertebral disc (IVD) model using a finite element (FE) analysis.

METHODS

A healthy male volunteer was recruited for the purposes of the study and a spiral computed tomography scan was subsequently conducted to obtain the data information in relation to the L4/5 motion segment. An FE model of the L4/5 motion segment constructed, on the basis of which degenerative IVD, IVD with NP removal, and IVD with NP replacement were in turn built. The stress distribution of the CEP and bulging of IVD were estimated using various motion states, including axial loading, forward flexion, backward extension, left axial rotation, and right axial rotation.

RESULTS

Under different motion states, the vertebral stress was higher in the degenerative IVD, the IVD with NP removal, and the IVD with NP replacement, in comparison to that of the normal IVD. Furthermore, a higher vertebral stress was detected in the degenerative IVD than the IVD with NP removal and the IVD with NP replacement. An even distribution of vertebral stress was observed in the IVD model with an artificial NP replacement, while the vertebral stress and bulging displacement were lower than after NP removal. Our findings provided confirmation that stress of the CEP was consistent with the vertebral stress.

CONCLUSION

This study provided evidence suggesting that NP replacement, vertebral stress, and bulging displacement are lower than that of degenerative IVD and IVD with NP removal under different motion states.

Molecular interactions between human cartilaginous endplates and nucleus pulposus cells: a preliminary investigation

STUDY DESIGN

Conditioned media (CM) of cartilaginous endplates (CEPs) of intervertebral discs were analyzed in a bioassay with regard to their influence on matrix turnover and inflammatory factors on nucleus pulposus (NP) cells of the same patient. CEP tissue underwent further histological and ultrastructural analysis.

OBJECTIVE

To identify possible interactions between the CEP and the disc via molecular factors that may influence disc matrix degradation and to determine degenerative changes of CEP tissue.

SUMMARY OF BACKGROUND DATA

Impaired endplate perme-ability due to degeneration and calcification is considered to be a key contributor to disc degeneration. An upregulation of metalloproteinases and inflammatory cytokines has been observed in degenerated intervertebral discs. Possibly, the CEP contributes to the regulation of disc matrix degradation via molecular interactions with the disc tissue.

METHODS

CEP and NP cells from the same patients (n = 6) were investigated in a bioassay with regard to their influence on matrix turnover and inflammatory factors. We determined gene expression of NP cells in alginate beads that were exposed to CM of CEP punches (CEP-CM) from the same patients. The CEP-CMs were analyzed by protein array for inflammatory cytokines. Further CEP samples underwent histological (n = 15) and ultrastructural analysis (n = 8) to determine alterations of cell and matrix structure.

RESULTS

NP cells exposed to their donor-corresponding CEP-CM significantly upregulated interleukins (IL-6, IL-8) and matrix metalloproteinase (MMP-3, MMP-13) expression, and significantly decreased aggrecan and collagen type 2 expression. Proinflammatory cytokines were identified in the CEP-CM. The occurrence of apoptotic cells and degraded matrix fragments varied strongly between donors.

CONCLUSION

Our results indicate interactions between the CEP and the NP tissue via molecular factors that upregulate matrix degrading enzymes and inflammatory cytokines and thereby influence the pathophysiology of disc degeneration. Ongoing investigations will further identify the regulative role of potential molecular factors that are responsible for these degenerative alterations.

LEVEL OF EVIDENCE

N/A.

Experimental animal models in scoliosis research: a review of the literature

BACKGROUND CONTEXT

Many animal species and an overwhelming variety of procedures that produce an experimental scoliosis have been reported in the literature. However, varying results have been reported on identical procedures in different animal species. Furthermore, the relevance of experimental animal models for the understanding of human idiopathic scoliosis remains questionable.

PURPOSE

To give an overview of the procedures that have been performed in animals in an attempt to induce experimental scoliosis and discuss the characteristics and significance of various animal models.

STUDY DESIGN

Extensive review of the literature on experimental animal models in scoliosis research.

METHODS

MEDLINE electronic database was searched, focusing on parameters concerning experimental scoliosis in animal models. The search was limited to the English, French, and German languages.

RESULTS

The chicken appeared to be the most frequently used experimental animal followed by the rabbit and rat. Additionally, scoliosis has been induced in primates, goats, sheep, pigs, cows, dogs, and frogs. Procedures widely varied from systemic to local procedures.

CONCLUSIONS

Although it has been possible to induce scoliosis-like deformities in many animals through various ways, this always required drastic surgical or systemic interventions, thus making the relation to human idiopathic scoliosis unclear. The basic drawback of all used models remains that no animal resembles the upright biomechanical spinal loading condition of man, with its inherent rotational instability of certain spinal segments. The fundamental question remains what the significance of these animal models is to the understanding of human idiopathic scoliosis.

Correlations between effective permeability and marrow contact channels surface of vertebral endplates

Homeostasis of the intervertebral disc relies on nutrient supply and waste clearance through the dense capillary network that is in contact with the cartilage endplate (CEP). We developed a micro-computerized tomography (micro-CT) method to quantify the marrow contact channel surface (MCCS) with the CEP and to validate the hypothesis according to which MCCS was correlated to the effective permeability of the vertebral endplate (VEP) and influenced by the mechanical stimuli. The influence of compression loading on local vascularization was investigated. Six 4-week-old skeletally immature pigs were instrumented with left pedicle screws and rod at both T5-T6 and L1-L2 levels to create asymmetrical spine tethers. After 3 months of growth, three cylindrical specimens of the VEP (one central and two lateral right and left) were obtained from both the instrumented and the control levels. We used a previously validated method for measuring permeability. Micro-CT analysis (resolution 12 microm) yielded a gray-scale 2D-image of the discal end of each specimen converted into a binary 2D-image to derive the MCCS. Correlations between MCCS and effective permeability were assessed. Effective permeability and MCCS were significantly decreased compared to the control group especially on the tethered side (-41.5%, p = 0.004 and -52.5%, p = 0.0009, respectively). Correlations were significant and showed maximal value (r(2) = 0.430, p < 0.0001) on the tethered side involving maximal compressive loadings. Mechanical stimuli, due to unbalanced growth, altered the vascularization and the convective properties of the CEP. The cascade of mechanobiological events should offer perspectives for research on disc degeneration and attempted treatment.