Fig. 1. Correlation between cytokine expression levels and the degree of intervertebral disk (IVD) degeneration according to the Pfirrmann grading system and magnetic resonance imaging. A gradual increase in the tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) expression levels was observed with the progression of IVD degeneration. The nerve growth factor (NGF) exhibited a minimal decrease. NS, not significant. *p <0.05.
