Variables affecting disc size in the lumbar spine of rabbits: anesthesia, paralysis, and disc injury

Evaluation of Intervertebral Disc Space Width Between 10th and 11th Thoracic Vertebrae in Cats Using Radiography and Magnetic Resonance Imaging

BACKGROUND

It is well known that the T10-T11 intervertebral disc space is usually narrower than the adjacent intervertebral disc spaces in most dogs. However, whether the T10-T11 disc space is narrower than the adjacent disc spaces is not well-established in cats.

OBJECTIVES

To measure the intervertebral disc space width of the T10-T11 disc space and to compare it with that of the adjacent disc spaces using radiography and magnetic resonance imaging (MRI).

METHODS

In Groups 1 (101 clinically normal cats) and 2 (32 cats without spinal diseases from T8 to T13), dorsal width (DW), central width (CW) and ventral width (VW) of the T8-T13 disc spaces were measured by radiography or MRI. Significant differences of the DW, CW and VW among disc spaces measured by radiography and MRI were evaluated. Intra- and interobserver reliabilities were measured by intraclass correlation coefficient.

RESULTS

In Groups 1 and 2 using radiography, the DW and CW of the T10-T11 disc space were significantly narrower than those of adjacent disc spaces (p < 0.05). The DW of the T8-T12 disc spaces was significantly narrower than that of the T12-T13 disc space in Group 1 using radiography. In Groups 1 and 2 using radiography, the CW and VW of the T8-T11 disc spaces were significantly narrower than those of the T11-T13 disc spaces. In Group 2 using MRI, the DW of the T10-T11 disc space was significantly narrower than that of the T11-T13 disc spaces. The VW of the T8-T11 disc spaces was significantly narrower than that of the T11-T13 disc spaces.

CONCLUSION

The T10-T11 intervertebral disc space on radiography is statistically narrower than the adjacent intervertebral disc spaces in normal cats. The cranial thoracic intervertebral disc spaces (T8-T11) are usually narrower than the caudal thoracic intervertebral disc spaces (T11-T13) on radiography and MRI.

Quantitative differences in intervertebral disc-matrix composition with age-related degeneration

This study was carried out to determine the effect of age on the intervertebral disc, using a rabbit model. Anulus fibrosus and nucleus pulposus tissue from New Zealand white rabbits aged 3 years old (old rabbits) and 6 months old (young rabbits) were used. The water content, the proteoglycan, the DNA content, and the mRNA levels of aggrecan, type I collagen, and type II collagen were all measured for each sample. Water, proteoglycan, DNA, and the mRNA levels of aggrecan and type II collagen were all greater in the nucleus pulposus of the young rabbits as compared to the old. For the anulus fibrosus, the difference between young and old is less marked with only proteoglycan and DNA being greater in the young disc as compared to the old. Clearly, according to our results, it is the nucleus pulposus that suffers the brunt of the changes with age.

Are animal models useful for studying human disc disorders/degeneration?

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

The effects of calcium channel antagonist nimodipine on end-plate vascularity of the degenerated intervertebral disc in rats

The vascular channels at the end-plate of the intervertebral disc are very important in maintaining a healthy disc. With age, a reduction of the nutrition of the avascular nucleus pulposus is inevitable. On the other hand the calcium channel antagonist nimodipine has been shown to have a positive effect on blood flow in the region of the vertebral end-plate. To evaluate the effects of nimodipine on the end-plate vascularity in the degenerative discs, we have produced an experimental disc degeneration and evaluated the radiological and histopathological features of the end-plate of the degenerated discs. Adult rats were divided into 3 groups: control (n=5), operated degeneration (n=5), and nimodipine treatment (n=5). Using a posterior approach, a cut was made parallel to the end-plates in the posterior annulus fibrosus in 5 consecutive intervertebral discs between the 5th and 10th vertebral segments of the tails of adult Swiss Albino rats. At 8 weeks, 5 of these animals were treated with nimodipine. In each experimental group, 1 animal was examined using computed tomography (CT) to study the density of the cartilage end-plate of the disc. Then, the animals were sacrificed for subsequent histopathological evaluation. We found that the vascular channel counts and percentage areas from animals treated with nimodipine were higher than from both the non-operative control and operated degeneration groups, although these were not statistically different. Accordingly, the profile of the density histogram in the nimodipine-treated group showed a wide plateau, indicating an increase in the vascularity in this region. From our results, we suggest that nimodipine enhances vascularisation of the cartilage end-plate in the disc. It is possible that the increased proportion of vascular contacts at the end-plate has a beneficial effect in the nutrition of the disc. However, further experimental studies will be needed to determine the validity of this statement in animals or human beings.

Comparative gene expression profiling of normal and degenerative discs: analysis of a rabbit annular laceration model

STUDY DESIGN

A rabbit annular laceration model was used to investigate intervertebral disc gene expression in normal and lacerated discs.

OBJECTIVES

To determine and compare the pattern of expression of potentially important genes in normal and lacerated discs and to determine if the changes in gene expression were similar to human degenerative discs.

SUMMARY OF BACKGROUND DATA

Little is known regarding gene expression in normal or degenerating disc tissue.

METHODS

Eighteen rabbits were subjected to annular laceration of the L1-L2 and L2-L3 discs while two rabbits served as sham controls. Control and lacerated discs were harvested 1 week, 3 weeks, and 6 weeks following surgery and subjected to histologic examination and gene expression analysis using the reverse transcription-polymerase chain reaction (RT-PCR). The genes studied included collagen Type I (Col I), collagen Type II (Col II), decorin, fibronectin (FN), interleukin-1a (IL-1alpha), bone morphogenetic protein 2 (BMP-2), Fas, matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 9 (MMP-9), matrix metalloproteinase 13 (MMP-13), and tumor necrosis factor (TNF). Expression levels of each gene were normalized to that of glyceraldehyde-3-phosphate dehydrogenase (GADPH), a constitutively expressed gene.

RESULTS

Histology confirmed progressive degeneration of the discs over the 6-week study period. Different patterns of gene expression were observed in control and lesioned discs. Annular laceration caused a marked upregulation (two- to eightfold) of the expression of Col I, Col II, FN, MMP-1, MMP-9, MMP-13, and Fas genes, whereas that of BMP-2, IL-1alpha, and TNF genes was unaffected. Expression of the decorin gene was downregulated approximately sixfold after annular laceration.

CONCLUSION

Annular laceration in this animal model resulted in marked changes in gene expression. Upregulation of gene expression was observed for some molecules found at high concentration in human degenerated discs, suggesting similarities to human disc degeneration at the molecular level. This supports the need for further study of the genes found to be activated by annular laceration.

Effect of Nd:YAG laser on experimental disc degeneration. Part I. Biochemical and radiographical analysis

Intervertebral disc herniation is an important health problem from both the social and economic aspect. It is often accompanied by a decrease in the content of water and proteoglycan (PG). The present study was undertaken to elucidate the effect of neodymium-yttrium-aluminum-garnet (Nd:YAG) laser on degenerated disc tissue. In this study a ventral disc herniation model in guinea pigs was performed to study the effects of ND:YAG laser on degenerated disc with low water and PG content. Effect of ND:YAG laser on degenerated cervical disc tissue is examined from the aspects of biochemistry and radiology. In the acute period water, PG, and collagen content decreased due to the ablative effect of ND:YAG laser on disc tissue. When changes in the degenerated disc in the post-laser chronic period were compared with degenerated disc findings, statistically significant changes could not be be found. From the results of this study, there is no question that the Nd:YAG laser offers many potential benefits, it remains to be proven whether or not this is of real benefit in the treatment of patients with degenerated disc disease.

A method for radiographic evaluation of pedicle screw violation of the vertebral endplate. Technique

STUDY DESIGN

This study evaluated the utility of intraoperative radiographs for minimizing the risk of pedicle screw tip violation of the superior vertebral endplate.

OBJECTIVES

An intraoperative radiographic technique is demonstrated that ensures that a screw has not penetrated the intervertebral disk.

SUMMARY OF BACKGROUND DATA

Although methods to avoid penetration of the medial pedicle cortex and the anterior body cortex have been described, no study has discussed screw penetration of the superior endplate and disc.

METHODS

Pedicle screws were inserted into 11 cadaveric lumbar spines, randomly, with the tip interior to the endplate, at the endplate, and through the endplate. Radiographs were evaluated to measure the penetration, if any, of the screws. Spine segments were dissected and evaluated anatomically. The anatomic and radiographic results were then compared.

RESULTS

The overall error rate for radiographs was 22/312 (7%). Oblique radiographs gave a much higher error rate.

CONCLUSIONS

A true lateral or anteroposterior radiographic view of the vertebra provides a high degree of certainty that the screw has not crossed the endplate when a "safe zone" of 3 mm remains superior to the screw tip. Intraoperative radiography can reduce concern about violation of the superior vertebral endplate.