Intra- and inter-rater reliability of spinal flexibility measurements using ultrasonic (US) images for non-surgical candidates with adolescent idiopathic scoliosis: a pilot study

  • Mahdieh Khodaei
  • Doug Hill
  • Rui Zheng
  • Lawrence H. Le
  • Edmond H. M. Lou
Original Article



This study aimed to determine the intra- and inter-rater reliabilities of spinal flexibility measurements using ultrasound imaging on non-surgical candidates with adolescent idiopathic scoliosis (AIS).


Twenty-eight consecutive consented AIS subjects (25 F; 3 M) were recruited; 24 subjects’ data were used for analysis. This study explored curve magnitude differences between standing, prone and voluntary maximum side-bending postures to assess the reliability of spinal flexibility (SF). Two raters were included in this study. Four flexibility indices, PRSI, BRPI, B-PRSI, BRSI, based on the postural changes from standing to prone and from prone to bending position were defined. The reliability analysis was evaluated using the intra-class correlation coefficient (ICC) [1, 2] and the standard error of measurements (SEM).


The ICC [1, 2] values of the intra-rater (R2 only) and inter-rater (R1 vs R2) reliabilities of the measurements (PRSI, BRPI, B-PRSI, BRSI) were (0.82, 0.64, 0.78, 0.91) and (0.78, 0.76, 0.84, 0.94), respectively. Among the four indices, the BRPI had the highest SEM values 1.42, and 0.73 for intra- and inter-raters results, respectively, while BRSI had the lowest SEM 0.04 and 0.02 for intra- and inter-rater, respectively.


The BRPI, BRSI and B-PRSI could be measured reliably on US images when the Cobb angle at prone position was not close to zero. Using these three indices, information may provide more comprehensive information about the SF. Validity of spinal flexibility measurements still needed to be confirmed with a clinical study with more subjects.

Graphical abstract

These slides can be retrieved under Electronic Supplementary Material.


Ultrasound imaging Spinal flexibility Flexibility indices Adolescent idiopathic scoliosis Reliability 



The difference between BRSI and PRSI indices


Bending Relative to Prone Index


Bending Relative to Standing Index


Intra-class correlation coefficient




Mean absolute difference


Main Thoracic




Prone Relative to Standing Index


Rater 1


Rater 2


Standard Deviation


Standard error of measurements


Spinal flexibility


Trial 1


Trial 2






Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

586_2018_5546_MOESM1_ESM.pptx (857 kb)
Supplementary material 1 (PPTX 857 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Radiology and Diagnostic ImagingUniversity of AlbertaEdmontonCanada
  2. 2.Department of Electrical and Computer Engineering, 11-371 Donadeo Innovation Centre for EngineeringUniversity of AlbertaEdmontonCanada
  3. 3.Department of SurgeryUniversity of AlbertaEdmontonCanada

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