• Chan Sam Moon, Tae-Hong Lim, Junghwa Hong, Donggeun Sul, and Nackhwan Kim.
• Graduate School of Medicine, Korea University College of Medicine, Seoul, Republic of Korea.
• Pain Physician. 2023 May 1; 26 (3): E181E189E181-E189.

BackgroundChronic discogenic pain includes degeneration-driven changes under the mechanical macroenvironment of an internal disc, which leads to the progressive changes of biochemical microenvironment that induce abnormal ingrowth of the nociceptor. The propriety of the animal model reflecting the pathologic natural history has not been assessed.ObjectivesThis study investigated the biochemical evidence of chronic discogenic pain by employing a discogenic pain animal model induced by shear force.Study DesignAnimal study utilizing rats in vivo model of a shear force device.MethodsFifteen rats were divided into 3 groups (n = 5/group) according to the period for which sustained dorsoventral shear force was applied (1 week or 2 weeks); the control group received the spinous attachment unit, without a spring. Pain data were collected using von Frey hairs on the hind paws. Growth factor and cytokine abundance was analyzed in the dorsal root ganglion (DRG) and plasma.ResultsAfter the shear force devices were installed, the significant variables were found to markedly increase in the DRG tissues of the 2-week group; however, they were not altered in the 1-week group. Specifically, interleukin (IL)-6, neurogrowth factor (NGF), transforming growth factor (TGF)-alpha, platelet-derived growth factor (PDGF)-beta, and vascular endothelial growth factor (VEGF) were increased. Meanwhile, the plasma levels of tumor necrosis factor-alpha, IL-1beta, IL-5, IL-6, IL-12, and NGF were increased in the 1-week group; whereas, TGF-alpha, PDGF-beta, and VEGF were increased in the 2-week group.LimitationsThe limitations include the general limitations of quadrupedal animals, the poor precision and flexural deformation of shear force devices, inaccuracies regarding the evaluation of histological denaturation, and short intervention and observational periods.ConclusionsThis animal model effectively generated biochemical responses to shear loading with evidence of neurological changes induced without direct macrodamage to the outer annulus fibrosus. Chemical internals were induced by mechanical externals among the contributing factors of chronic discogenic pain.

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