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Displacement Index of Pizzutillo et al in a Patient with Spondylolisthesis

Description

Pizzutillo et al proposed the displacement index for patients with spondylolisthesis. This is an objective method for documenting the changes in the relationship of L5 to S1 in lateral radiographs. It is less dependent on specific landmarks that may be hard to measure precisely because of the secondary changes that occur with disease progression. The authors are from the Alfred I duPont Institute in Wilmington, Delaware.


 

Imaging study required: lateral X-ray of the lumbar spine and pelvis

 

Lines required: A line drawn through the superior and inferior corners of the dorsal surface of S1 is extended to the level of L3 (dorsal sacral line).

 

Measurements:

(1) length of the superior aspect of the L5 vertebral body (between the anterior and posterior corners) = length B

(2) length of a perpendicular line between the dorsal sacral line and the posterior corner of the L5 vertebral body = length A

 

displacement index =

= (length A) / (length B)

 

difference in the displacement index =

= (current displacement index) - (last displacement index)

 

Interpretation:

• minimum difference: 0

• A difference >= 0.1 indicates a true radiographic change in the anterior translation, rotation or axial convergence of L5 on S1. This may not necessarily be a clinically significant change.

 


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