A novel in vivo porcine model of intervertebral disc degeneration induced by cryoinjury.

PURPOSE: Degenerative disc disease involves sequential events that lead to the loss of cells, a decrease in disc matrix production, disc dehydration, and alteration of its biomechanical properties. The aim of this study was to determine whether cryoinjury of the nucleus pulposus performed through endplate perforation contributes to disc degeneration and to compare this technique with standard methods.

METHOD: Under general anesthesia, the lumbar discs of six pigs were exposed and randomly submitted to needle puncture of the annulus fibrosus (NeP), isolated endplate injury (EP), or cryoinjury using a 2.5-J Thompson cryoprobe applied through a single endplate perforation (EP+cryo). The remaining discs served as controls. Animals were sacrificed at two months and the harvested lumbar spines were submitted to CT scan and MRI investigations. Histologic analysis was performed to assess the degree of disc degeneration.

RESULTS: CT scan showed that decrease in average disc height was more important after cryoinjury (49.3%) than after endplate perforation (16.9%) (P < 0.0001) or needle puncture (19.4%) (P < 0.0001). On MRI, the dehydration ratio was significantly more important after EP+cryo (60%) than after NP (40%) or EP (30%) (P < 0.0001). After cryoinjury, the histologic score developed for this study was significantly higher than after needle puncture or endplate perforation (P < 0.0001).

CONCLUSIONS: Imaging and histological analysis showed that disc cryoinjury applied through endplate perforation was superior to the classical NeP and EP models to induce experimental disc degeneration. This model appears suitable for testing safety and efficacy of novel treatments of intervertebral disc degeneration.