Vertebral Endplate Defects Induced Mechanical Alterations and Disc Calcification

Abstract

Study Design Cross sectional comparative study. Objectives The current study aims to explore the calcification potential (BMP2 expression) of intervertebral discs and its association with the presence of vertebral endplate defects visible on MRI. Methods Forty-seven herniated lumbar disc samples obtained from patients aged 20-76 (31 M/16F) undergoing surgery. Five-µm thin sections were stained with H&E in order to assign a histological degeneration score (HDS) from 0-15 on the basis of cell density (0-5), structural alterations (0-4), granular changes (0-3) and mucus degeneration (0-3). Sections were immuno-stained with anti BMP-2 antibodies to observe the calcification potential in these discs. In addition, pre-operativeT2-T1 W MRI images of the lumbar spine were analyzed for the presence and type (typical or atypical) of vertebral endplate defects, grade of disc degeneration (Pfirrmann grade I-V), presence of high intensity zones (HIZ), and Modic changes at the operated level. Results Vertebral endplate defects, Modic changes & HIZ were observed in 81%, 29% and 21% of patients respectively. Mean HDS & BMP-2 expression was 9 ± 2 and mean 71 ± 36 spots/mm2 respectively. Discs with adjacent vertebral endplate defects showed increased cell density ( P = .004), mucus degeneration ( P = .002), HDS ( P = .01) and BMP-2 expression ( P = .01). Discs with HIZ also had increased HDS, but significance was seen with increased BMP2 expression ( P = .006). HDS showed a positive correlation with BMP 2 expression (r = .30, P = .04). Conclusion These findings suggest that the altered mechanical environment of discs is strongly associated with BMP-2 expression which is an important marker of intervertebral disc calcification.