Advancements in Characterization of Cartilaginous Endplates using Magnetic Resonance Imaging

The critical role of the cartilaginous endplate (CEP) in disc health and degeneration is becoming increasingly evident. CEP can influence the disc degeneration process impairing the disc’s nutrient transport and supply, and the disc function. Thus, a characterization method able to point out correlations between CEPs and disc degeneration is necessary. The objectives of this study were to quantify the 3D CEP thickness using 3D experimental ultrashort echo time (UTE) MRI sequences to investigate relationships between CEP thickness and disc level, Pffirmann grade, CEP anatomical zone and site, and to assess correlations between IVD and CEP thickness. To do so, four cadaveric lumbar spines with varying degrees of disc degeneration were scanned with three 3D UTE sequences - Echo1, Echo2, and high-resolution - in the sagittal plane, and Echo1 and Echo2 were then subtracted. Next, 3D CEP surface MRI-derived models were defined and the CEP shells (superior and inferior) were created. The CEP and IVD thicknesses were measured from the CEP shells, as point-plane distance, and CEP distribution maps based on anatomical quadrants were defined. The MRI-derived CEP thickness values were validated against standard histology measurements. From the results, the CEP distribution maps demonstrated a qualitative heterogeneity in thickness between specimens and disc levels. Statistical comparisons showed that CEP thickness influential factors were the disc level and Pfirrmann grade (p-value$\mathbf{<}$0.05), correlations between IVD and CEP thickness defined low negative trends for both cranial and caudal CEPs (cranial: Pearson’s coefficient=-0.22; caudal: Pearson’s coefficient=-0.34), while the comparison between histologic and MRI-based measurements of CEP thickness had a low positive correlation (Pearson’s coefficient=0.37). In conclusion, this study introduced an innovative method to quantify the 3D CEP thickness with distribution maps based on anatomical quadrants plus, although the low positive correlation with histology, the UTE-derived results suggested that the influential factors - disc level and Pfirrmann grade - and the low negative relationship between IVD and CEP thickness may serve as diagnostic markers for disc degeneration.