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Cobb angle measurement with a conventional convex echography probe and a smartphone

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Background context

Serial X-rays are needed during the follow-up of adolescent idiopathic scoliosis. They are done every 6 or 3 months in cases of high risk of progression. Thanks to the advances in ultrasound techniques, deformity measurement systems free from ionizing radiations have been validated, although spinal surgeons did not use them routinely due to the need of special software.


The aim of our work is to assess the reproducibility and correlation of an ultrasound measuring system based on the positioning of the transverse processes.

Study design

Prospective, single center, randomized, triple blinded.


Two independent researchers trained in ultrasound examined the spinal deformities of 31 children. The measurements were compared against those performed with an X-ray by three scoliosis expert surgeons. Statistics were performed by an independent researcher. Parametric methods were used.


We found a 95% [(0.91–0.97) p < 2.2e−16] correlation between the degree of scoliosis measured with the proposed ultrasound system and the 30 cm × 90 cm X-rays in standing position. There was an intra-observer reliability of 97% [r-squared = 0.97; CI 95% (0.95–0.98) p < 2.2e−16] and an inter-observer reliability of 95% [r-squared = 0.95; CI 95% (0.90–0.97) p < 2.2e−16].


An approximation of the Cobb angle measure is possible with ultrasound by using the transverse processes as reference. This is a very rapid and simple system for assessing the principal spinal deformity measure in young people, although it does not allow estimating the associated axial or sagittal rotation.

Graphic abstract

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Special mention to Isabel Llorenç and to Teresa Rodríguez for their ideas and commitment to the project.


The study was approved by the Medical Ethics Committee of the institution (2017/0619).

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Correspondence to Joan Ferràs-Tarragó.

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Ferràs-Tarragó, J., Valencia, J.M.M., Belmar, P.R. et al. Cobb angle measurement with a conventional convex echography probe and a smartphone. Eur Spine J 28, 1955–1961 (2019).

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