A Momentary Impact Injury of Vertebral Endplates, even without Structural Disruption, Initiates Disc Degeneration In Vitro.

Abstract

Background ： It has been acknowledged that the intervertebral disc degeneration(IDD) is associated with an aberrant cell-medicated response to structural failures, such as vertebral burst fracture, radial fissures, and endplate fracture. However, whether a momentary impact injury of the endplates without structural disruption, is sufficiently to initiate disc degeneration remains elusive. This study was to further evolve an in vitro momentary impact injury model of IDD and to investigate if a momentary impact load of the endplates without structural disruption could initiate IDD. Methods. Rat spinal segments (from L1/2 to L5/6, n=54) were harvested and randomly assigned into three groups: Control (n=18), Low Impact (12 J/cm 3 , n=18) and High Impact (25 J/cm 3 , n=18). Samples in both of the impact groups were subjected to axial momentary impact load using a custom-made apparatus, and cultured for 14 days. The degenerative process was investigated by using histomorphology and real-time PCR. Results: The discs in both of the impact groups showed significant degenerative changes at 14 days, both of which showed much higher histological scores and up-regulation of the catabolic (MMP-9, MMP-13) genes transcription than that of the control group ( P ＜0.05). The discs with endplate fracture compared to that with intact endplate also showed strongly up-regulated catabolic (MMP-9, MMP-13) genes transcription, and more significant degenerative changes based on the histological scoring ( P ＜0.05). Conclusion: This study demonstrated that a momentary impact load (12 J/cm 3 ) on the spinal segments of the rats could initiate IDD at 14 days after injury and not only endplate fracture but also a momentary impact injury without structural disruption could also promote IDD.