1) Description of Measurement

The Disc-Height Index (DHI) is a normalized metric that quantifies intervertebral disc height relative to adjacent vertebral body height. By expressing disc height as a ratio, DHI minimizes magnification and patient-size variability and serves as a sensitive marker for disc degeneration, collapse, and segmental instability.

2) Instructions to Measure

•  Identify the disc level to be evaluated on the mid-sagittal MRI.

•  Measure disc height at three locations:

• Anterior disc height (A)
  
  

• Middle disc height (M)
  
  

• Posterior disc height (P)
  
  

• Calculate the mean disc height (DH):

DH = (A + M + P)/3

• Measure the heights of the vertebral bodies immediately above (V₁) and below (V₂) the disc at their midpoints.

• Calculate the Disc-Height Index (DHI):

DHI = DH/(V1 + V2)/2

3) Normal vs. Pathologic Ranges

• Normal DHI: ≥ 0.40

• Mild disc height loss: 0.30 - 0.39

• Moderate degeneration: 0.20 - 0.29

• Severe disc collapse: < 0.20

Key points:

• Progressive reduction in DHI correlates with Pfirrmann grades IV–V, facet arthropathy, and instability.

• Comparison to adjacent segments improves accuracy.

4) Important References

Chen X, Sima S, Sandhu HS, et al. Radiographic evaluation of lumbar intervertebral disc height index: An intra and inter-rater agreement and reliability study. J Clin Neurosci. 2022 Sep;103:153-162. doi: 10.1016/j.jocn.2022.07.018.

Snowden R, Miller J, Saidon T, et al. Does index level sagittal alignment determine adjacent level disc height loss? J Neurosurg Spine. 2019 Jun 21;31(4):579-586. doi: 10.3171/2019.4.SPINE181468.

Chen IR, Wei TS. Disc height and lumbar index as independent predictors of degenerative spondylolisthesis in middle-aged women with low back pain. Spine (Phila Pa 1976). 2009 Jun 1;34(13):1402-9. doi: 10.1097/BRS.0b013e31817b8fbd.

5) Other info....

DHI is useful for longitudinal studies to track disc degeneration progression.

Should be reported together with:

• Pfirrmann grade

• Modic endplate changes

• Segmental alignment (spondylolisthesis, kyphosis)