Validity and test-retest reliability of photogrammetry in adolescents with hyperkyphosis

A variety of noninvasive instruments have been introduced in the literature to assess thoracic curvature, although the psychometric properties of many of these instruments have not been satisfactory. Photogrammetry is a safe, accessible, and reliable technique. However, its validity in adolescents with hyperkyphosis has not yet been investigated.

To investigate the validity and test-retest reliability of photogrammetry in the measurement of thoracic kyphosis among adolescents with hyperkyphosis.

Fifty adolescents with hyperkyphosis participated in this study. The kyphosis angle was measured using radiography and photogrammetry. A two-way random model of the intraclass correlation coefficient (ICC_2,3) was used to estimate relative reliability. Absolute reliability was assessed by calculating the standard error of the measurements (SEM) and the minimal detectable change (MDC). Pearson's correlation coefficient was calculated to evaluate the validity of the photogrammetry technique. Bland-Altman plots were plotted to determine the agreement between the angles measured by radiography and photogrammetry.

There was a strong correlation between the values obtained from the photogrammetry technique and those from the radiography method (r = 0.94). The 95% limits of agreement indicated that the photogrammetric measurements of thoracic kyphosis angle might range from 2.4 degrees greater to 10.2 degrees lower than the Cobb radiographic angle. Photogrammetric measurements of thoracic kyphosis showed excellent test-retest reliability (ICC = 0.97; SEM = 1.67; MDC = 4.62).

High reliability of photogrammetry technique and its strong correlation with radiographic Cobb angle support the application of this technique for the measurement of thoracic kyphosis in clinical practice.