Evaluating the Impact of Mechanical Manipulation on Inducing Disk Degeneration: A 3-Month Radiologic Follow-Up of Intervertebral Disk Degeneration in a Needle-Punctured Rat Tail Model

Abstract

Introduction The rat tail model for the intervertebral disk degeneration has recently been receiving a high level of interest among the intervertebral disk degeneration studies. A better understanding of the time course and recognizing the role of mechanical manipulation may lead to development of a more reproducible model for further application in disk implanting studies. In this study, we aimed to establish a reproducible disk degeneration rat tail model by needle puncture and to assess the gradual progression of the degeneration over time. Materials and Methods Under fluoroscopic guidance, the fourth intervertebral disk space of the rat's tail in 13 mature Rowett Nude (RNU) male rats (T-Cell-Deficient, Athymic Nude Rats) was percutaneously stabbed on the left lateral side with an 18G needle. To standardize the depth of the stab, the tip of a syringe cap was cut at 5 mms point, and was then used with a new needle to puncture each new animal. The first seven rats (group 1) received no further mechanical manipulation; however in the next six rats (group 2), in addition to the needle puncture, the proximal portion of the tail including the stabbed level was then manually rotated around and compressed along to the longitudinal axis. Radiographic follow-up was carried out for 3 months; with X-rays performed at 1, 2, 4, 6, 10, and 12 weeks, and magnetic resonance imaging (MRI) scans at 4 and 12 weeks. Disk height change was evaluated by calculating the disk height index (DHI) on X-rays. In each animal, a baseline DHI was calculated based on the rostral healthy disc. Disk degeneration grade was also evaluated on T2-weighted MRI sequences based on the signal change in the annulus fibrosus and nucleus pulposus. A 1-4 modified Thompson grading system was used, defined as no, mild, moderate, and severe degeneration. Statistical analysis was performed in all animals and in the two different groups. Results On X-rays, the mean disk height in all 13 rats showed significant decrease at both 1 week and 2 weeks, with the maximum decrease observed at 2 weeks. The disk height increased gradually between 4 to 12 weeks; however it was not statistically significant. In the separate analysis of the two different groups, the second group had a similar significant decrease in disk height at 1 and 2 weeks. Despite minor changes, in the first group no statistical significance was detected. On T2-weighted MRI scans at 4 and 12 weeks, all rats had a statistically significant increase in disk degeneration grade, as compared to the baseline. However, the minor increase in degeneration grade between 4 weeks to 12 weeks was not statistically significant. On separate analysis, only the second group indicated significant increase in the disk degeneration grade after the puncture experience. The X-Ray results presented as DHIs and the MRI results described as the 1-4 modified Thompson grading system for intervertebral disk degeneration showed strong correlation in all 13 rats, and in each of the 2 groups separately. Conclusion Isolated needle puncturing of the intervertebral disk leads to significantly lower levels of degeneration compared to needle puncturing followed by further manual mechanical manipulation. The highest level of degeneration is observed at 2 weeks. Disk height decrease on X-Ray imaging and signal changes on T2-weighted MRI scans can provide good informative data on the level of degeneration. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared