Table 1. Classification of intervertebral disc degeneration on magnetic resonance imaging (MRI) by Pfirrmann et al [16].

Grade	Appearance on T2-weighted sagittal images of spine
Ⅰ	The structure of the disc is homogeneous, with bright hyperintense white signal and a normal disc height.
Ⅱ	The structure of the disc is inhomogeneous, with bright hyperintense white signal. Disc height is normal, with or without a horizontal gray band.
Ⅲ	The structure of the disc is inhomogeneous, with an intermediate gray signal intensity. Disc height is normal or slightly decreased.
Ⅳ	The structure of the disc is inhomogeneous, with hypointense dark gray signal intensity. Disc height is normal or moderately decreased,