Study design
Fourteen young volunteers, nine female and four male aged between 21 and 25 (mean ± SD: aged 22.14 ± 1.12 years), took part in this study. Participants were healthy, free of any injury or pain for at least a month prior to testing and did not have diagnosed scoliosis or Scheuermann disease. Subjects gave their written informed consent to participate in this examination. Table 1. shows the weight, height and Body Mass Index of the participants.
Examination was performed with the rasterstereographic measuring system Formetric 4D (Diers International GmbH, Schlangenbad, Germany). Parallel white light lines are projected on the back surface of the participant by the slide projector. The 3-dimensional back shape leads to a deformation of the parallel light lines, which can be detected by the camera. Anatomic landmarks are thereby automatically captured by assigning concave and convex areas to curved light pattern during 6 s [11]. Based on the automatic detection of the dorsal process of the seventh vertebral body (VP) and of the right and left lumbar dimple (DR and DL), the software was able to calculate the number of parameters. In this study 6 parameters were analyzed: Trunk inclination [deg], Pelvis inclination [deg], Distance between kyphosis apex and cervical lordosis apex (K-CL) [mm] , Distance between kyphosis apex and lumbar lordosis apex (K-LL) [mm], Kyphosis angle [deg], Lumbar lordosis angle [deg].
Position of the pelvis can be drawn because the lumbar dimples are in close relation to the underlying posterior superior iliac spines of the pelvis. Positive pelvis inclination means forward tilt and negative values mean backward tilt of the pelvis. Trunk inclination was calculated as the distance in the sagittal plane between the VP and the middle point between lumbar dimples. A positive value was interpreted as an increase in inclination in an anterior direction [12, 13]. Kyphosis angle was calculated between inflectional point cervicothoracic and inflectional point thoracolumbar, lumbar lordosis angle was calculated between inflectional point thoracolumbar and inflectional point lumbosacral. Rasterstereographic method previously occurred as a reliable tool for examination of healthy volunteers posture in the sagittal plane [14, 15].
According to previous studies, participants were instructed to stand with their feet shoulder-width apart, looking straight ahead [16]. First measure of spinal curvature and pelvic tilt was made during normal standing position in 6s period time. When asked, subjects flexed their arms to 90°. Spinal curvature and pelvic tilt were measured again (Matthiass 1, 0s+6 s). Participants were instructed to retain this posture for 30 seconds, after which time a third spinal curvature and pelvic tilt measurement was made (Matthiass 2, 30 s+6 s). After the third measure, participants were asked to lower down their arms. The program DIERS formetric 4D average (static trial, 2 frames/s, averaging 12 frames during 6s) was used for data collection and processing.
Statistical analysis
Statistical analysis was carried out using Statistica 13.1 analytics software. Shapiro-Wilk test revealed that the data were not normally distributed. Non-parametric tests were used for further statistical analysis. Three pairs of measurements (Matthiass1 vs Matthiass2; Matthiass1 vs standing position; Matthiass 2 vs standing position) were compared using Wilcoxon matched pairs test. Spearman rang correlation was calculated for all parameters during 3 measurements. Statistical significance was accepted at p < 0.05 with all outcome measures reported as median and ranges (minimum and maximum).