Fig. 4

Schematic of imaging measurements. A Disc height index (DHI), DHI = [2(b1 + b2 + b3)]/[(a1 + a2 + a3) + (c1 + c2 + c3)] * 100%. B, C Schematic diagram of sagittal translation (ST) and the range of motion (ROM). B The measurements in hyperextension position. C The measurements in hyperflexion position. ST = a1–a2, GROM = b2- (-b1), Adjacent segment ROM = c2- (-c1). D Ratio value of the greyscale (RVG). Midsagittal T2-weighted images were chosen, and RVG was the greyscale of discs (a) normalized against the greyscale of cerebrospinal fluid at the same level (b)