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Reliability of Tibial and Tibiofibular Torsion Indices Using Ultrasound and Mechanical Devices With an Inertial
Xavier Ruiz-Tarrazo1, Andrea Coda2, Carla Sánchez-Dueñas3
1Sport, Exercise, and Human Movement (SEaHM) Research Group. Faculty of Health Sciences at Manresa. University of Vic - Central University of Catalonia (UVic-UCC), Manresa, Spain; Faculty of Health Sciences at Manresa. University of Vic - Central University of Catalonia (UVic-UCC), Manresa, Spain.
Objective:
To assess the intra- and inter-observer reliability of two non-invasive tibial torsion indices in children-the ultrasound-based Tibial Torsion Index (TTI) and the mechanically based Tibiofibular Torsion Index (TFTI)-and to examine their agreement and child acceptability.
Materials And Methods:
Prospective reliability study in 20 healthy children aged 7-9 years (40 tibiae). TTI was obtained with ultrasound using standardized landmarks and a compact inertial measurement unit (IMU) mounted on the probe; TFTI with two mechanical devices using a single IMU sequentially. Two independent observers performed assessments (Observer 1 on Day 1 and Day 2; Observer 2 on Day 2). Reliability metrics included intraclass correlation coefficients (ICC(2,1), 95% CI), standard error of measurement (SEM) and smallest detectable change (SDC95). Intrasession variability was expressed as within-session SD. Agreement was evaluated using correlation, Bland-Altman plots and regression analyses. Child acceptability regarding pain, comfort and willingness to repeat was recorded on a Likert-type scale supported by a faces-based visual aid.
Results:
TTI showed excellent intra-observer (ICC(2,1) = 0.98) and good inter-observer reliability (ICC(2,1) = 0.86). TFTI showed good intra-observer (ICC(2,1) = 0.85) and moderate inter-observer reliability (ICC(2,1) = 0.70). SEM ranged 1.6°-3.8°; SDC95 4.4°-10.4°. Correlation between TTI and TFTI was weak (r = 0.35; ρ = 0.30); Bland-Altman indicated a mean difference of 14.7° with proportional bias. Acceptability was high (median comfort 5, pain-free 5, willingness-to-repeat 4/5).
Conclusion:
Both indices were reproducible. The ultrasound-based TTI demonstrated superior inter-observer reliability and may represent a child-friendly, radiation-free option for monitoring tibial torsion in pediatric practice.
