Testing the impact of discoplasty on the biomechanics of the intervertebral disc with simulated degeneration: An in vitro study

Percutaneous Cement Discoplasty has recently been developed to relieve pain in highly degenerated intervertebral discs presenting a vacuum phenomenon in patients that cannot undergo major surgery. Little is currently known about the biomechanical effects of discoplasty. This study aimed at investigating the feasibility of modelling empty discs and subsequent discoplasty surgery and measuring their impact over the specimen geometry and mechanical behaviour. Ten porcine lumbar spine segments were tested in flexion, extension, and lateral bending under 5.4 Nm (with a 200 N compressive force and a 27 mm offset). Tests were performed in three conditions for each specimen: with intact disc, after nucleotomy and after discoplasty. A 3D Digital Image Correlation (DIC) system was used to measure the surface displacements and strains. The posterior disc height, range of motion (ROM), and stiffness were measured at the peak load. CT scans were performed to confirm that the cement distribution was acceptable. Discoplasty recovered the height loss caused by nucleotomy (p = 0.04) with respect to the intact condition, but it did not impact significantly either the ROM or the stiffness. The strains over the disc surface increased after nucleotomy, while discoplasty concentrated the strains on the endplates. In conclusion, this preliminary study has shown that discoplasty recovered the intervertebral posterior height, opening the neuroforamen as clinically observed, but it did not influence the spine mobility or stiffness. This study confirms that this in vitro approach can be used to investigate discoplasty.