Comparing the reliability of the Goniometer Pro application and flexicurve for measuring thoracic kyphosis: a cross-sectional study

The most common spinal anomaly is thoracic kyphosis, which frequently occurs in adolescents and older people. The flexicurve is an instrument commonly used by physiotherapists to assess spinal curvature. However, advancing technology, particularly the rise of mobile applications, has resulted in the replacement of traditional methods. This study aimed to investigate and compare the intra-rater and inter-rater reliability of the smartphone-based Goniometer Pro application and the flexicurve in measuring the thoracic kyphosis angle among healthy university students. A total of 30 participants were assessed by two independent raters using the flexicurve and the Goniometer Pro App to measure the thoracic kyphosis angle. Agreement was assessed using intraclass correlation coefficients, standard error of measurement and minimal detectable change. The flexicurve demonstrated excellent intra-rater reliability (intraclass correlation coefficients=0.87 and intraclass correlation coefficients=0.85 for two raters) and good inter-rater reliability (intraclass correlation coefficients=0.60). Additionally, the standard error of measurement and the minimal detectable change values indicated small measurement errors for the flexicurve. Similarly, the Goniometer Pro application exhibited excellent intra-rater reliability (intraclass correlation coefficients=0.90 and intraclass correlation coefficients=0.89 for two raters) and inter-rater reliability (intraclass correlation coefficients=0.87), along with small measurement errors indicated by the standard error of the measurement and minimal detectable change values. The Goniometer Pro app demonstrated higher inter-rater reliability than the flexicurve when measuring the thoracic kyphosis angle. Consequently, it stands out as a recommended, user-friendly, and time-efficient tool for clinicians involved in the assessment and monitoring of thoracic kyphosis.