A new method of creating intervertebral disc disruption of various grades

BACKGROUND - The purpose of this study was to develop a model of intervertebral disc disruption capable of (1) internal disruption without excessive disruption to the disc surface, (2) user-defined disruption magnitude and location and (3) interrogation by magnetic resonance imaging. Present models of disc disruption may have some, but not all, of these features. METHODS - Intravenous tubes were inserted into the intervertebral discs of a cadaveric porcine lumbar spine. Tube placement in the inner annulus was confirmed by magnetic resonance imaging. Each disc was then injected through the intravenous tube with nitrogen gas at pressures of 69 kPa, 172 kPa, 345 kPa and 690 kPa. Before and after injection, edge detection analysis of magnetic resonance imaging images was used to quantify tissue disruption. These values were then multiplied by the thickness of the slices and summed to determine disruption volume for individual discs. Four additional discs were injected with the addition of ink, sectioned and then inspected visually. RESULTS - As the injection pressure increased, the gas volume within the annulus increased significantly as did visualized annular disruption. No significant difference in gas volume was observed between different discs injected with equal pressure. INTERPRETATION - As confirmed by magnetic resonance imaging and dissection, gas volume and tissue disruption within the annulus fibrosus were proportional to the pressure of injected nitrogen. This model of disc disruption promises to provide several advantages in the investigation of disc pathology including (1) user-controlled magnitude of inner annulus disruption, (2) user-controlled tissue disruption localization, (3) minimal disruption of the exterior annulus, (4) independence between the magnitude of external and internal disruption and (5) the ability to visualize resulting disruptions with magnetic resonance imaging.