Background context: Discectomy is a surgical technique commonly used to treat bulging or herniated discs causing nerve root compression. Clinical data suggest discectomy may also help patients with contained discs and no clear neural compromise. However, the mechanisms of clinical efficacy are uncertain, and consequently bases for treatment optimization are limited.
Purpose: To determine the effect of percutaneous plasma decompression on the histologic, morphologic, biochemical and biomechanical features of degenerating intervertebral discs.
Study design: An adult porcine model of disc degeneration was used to establish a degenerative baseline against which to evaluate discectomy efficacy.
Outcome measures: Cytokines interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor (TNF)-alpha were measured from tissue samples using enzyme-linked immunosorbent assay. Histology and morphology images were rated for degenerative findings (of cells and matrix) in both the nucleus and annulus. Proteoglycan content was determined, and intact specimen stiffness and flexibility were measured biomechanically. Magnetic resonance images were collected for biomechanical specimens.
Methods: Using a retroperitoneal surgical approach, stab incisions were made in four or five lumbar discs per spine in 12 minipigs. Animals were allocated into one of three groups: 6-week recovery, 12-week recovery and percutaneous plasma decompression using an electrosurgical device at 6 weeks with recovery for 6 additional weeks. Four additional animals served as controls.
Results: Discs treated with discectomy had a significant increase in IL-8 and a decrease in IL-1 as compared with the 12-week, nontreated discs. There were no significant differences in morphologic and biomechanical parameters or proteoglycan content between treated discs and time-matched, nontreated discs.
Conclusions: Our results demonstrate that percutaneous plasma discectomy alters the expression of inflammatory cytokines in degenerated discs, leading to a decrease in IL-1 and an increase in IL-8. Whereas both IL-1 and IL-8 have hyperalgesic properties, IL-1 is likely to be a more important pathophysiologic factor in painful disc disorders than IL-8. Therefore, the alteration in cytokine expression that we observed is consistent with this effect as a mechanism of pain relief after discectomy. In addition, given that IL-1 is catabolic in injured tissue and IL-8 is anabolic, our results suggest that a percutaneous plasma discectomy may be capable of initiating a repair response in the disc.