Peter Bernstein, Johannes Metzler, Marlene Weinzierl, Carl Seifert, Wadim Kisel, Markus Wacker

March 2021, Volume 30, Issue 3, pp 676 - 685 Original Article Read Full Article 10.1007/s00586-020-06577-3

First Online: 27 August 2020

Introduction and objective

Although being standard for scoliosis curve size estimation, COBB angle measurement is well known to be inaccurate, due to a high interobserver variance in end vertebra selection and end plate contour delineation. We propose a stepwise improvement by using a spline constructed from vertebra centroids to resemble spinal curve characteristics more closely. To enhance precision even further, a neural net was trained to detect the centroids automatically.

Materials & Methods

Vertebra centroids in AP spinal X-ray images of varying quality from 551 scoliosis patients were manually labeled by 4 investigators. With these inputs, splines were generated and the computed curve sizes were compared to the manually measured COBB angles and to the curve estimation obtained from the neural net.


Splines achieved a higher interobserver correlation of 0.92–0.95 compared to manual COBB measurements (0.83–0.92) and showed 1.5–2 times less variance, depending on the anatomic region. This translates into an average of 1° of interobserver measurement deviation for spline-based curve estimation compared to 3°–8° for COBB measurements. The neural net was even more precise and achieved mean deviations below 0.5°.


In conclusion, our data suggest an advantage of spline-based automated measuring systems, so further investigations are warranted to abandon manual COBB measurements.

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