Recapitulating the Spectrum of Intervertebral Disc Degeneration in a Large Animal Model

Images for quantitative T1δ and T2 mapping were obtained, as well as T2 weighted images for Pfirrmann grading. Correlations between quantitative MRI parameters and Pfirrmann grade were established by linear regression. Individual motion segments were then imaged using high resolution microcomputed tomography (μCT) to visualize and quantify morphologic changes to the vertebral bony endplate. Alcian blue (glycosaminoglycans) and picrosirius red (collagen) stained, mid-sagittal, histological sections were used to visualize degenerative changes. Sections were graded on a visual analog scale by three blinded observers in five categories: organization of the annulus fibrosus, nucleus pulposus matrix, annulus fibrosus/nucleus pulposus border, nucleus pulposus cellularity, and cartilage endplate structure. Five samples from each of the intact control, nucleotomy and 1U ChABC groups were utilized for biomechanical testing. Following overnight equilibration in PBS, samples were subjected to a testing protocol consisting of 20 cycles tension compression (2230N to 1115N), followed by 1 hour of creep at 2230N (0.48 MPa). Tension/compression data was fit to a sigmoid function and creep data was fit to a five parameter viscoelastic constitutive model for analysis. For quantitative outcome measures, statistically significant differences (p , 0.05) were established via one or two-way ANOVAs with Tukey’s post-hoc tests.