A model for intervertebral disc shape variation in a population including the effect of degeneration

The 3D shape of the intervertebral disc (IVD) is modeled in this work from a population of samples. Heretofore, 3D models of the disc have been created from individual samples only. L3/L4 discs were segmented from 14 magnetic resonance images. The mean shape was calculated using a signed distance function representation, and principal components analysis was used to re-express the residual variability with an orthonormal basis. The first basis vector, which represents lateral bulging of the disc, expresses the majority of the population´s shape variation. This vector was also significantly correlated with Pfirrmann grade (p<;0.01), a measure of disc degeneration. The IVD shape model can thus be used to generate an average IVD shape for the population, as well as shapes for specific degenerative grades.