Back surface measurements by rasterstereography for adolescent idiopathic scoliosis: from reproducibility to data reduction analyses.

PURPOSE: Aim of this cross-sectional study was to evaluate the reproducibility of back surface measurements obtained by rasterstereography (RS) in adolescents with idiopathic scoliosis (AIS), and to identify the most informative RS parameters through a multi-step reduction analysis approach. METHODS: Sixty-six AIS were assessed with a RS scanner. The assessment was repeated in the same day 15 min after the first scan and after 1 week. Intraclass-correlation analyses were conducted to verify the consistency of the measurements. A multi-step reduction technique including correlation, principal component analysis (PCA) and regression was employed to extract a core-set of key RS parameters. RESULTS: Back surface measures were obtained from 66 AIS aged 10-17 years (median 13), with a mild Scoliosis angle < 25 (median 20). The reliability over the 3 sessions proved high to very high, with all the intraclass correlation coefficients ≥ 0.8 and 32 out of 48 coefficients ≥ 0.9. Only 8 of the 12 parameters provided by the RS device showed significant inter-item correlations and were therefore considered for further analyses. PCA extracted 4 of them, which entered the final regression analysis. High beta coefficients were found for 2 predictors: "Surface rotation-rms" and "Side deviation-rms," which were found to be significantly associated with the dependent variable "Scoliosis angle." CONCLUSIONS: Data showed that RS measurements are reliable in AIS with mild severity of scoliosis. "Surface rotation" and "Side deviation" were the best descriptors of the Scoliosis angle and should be considered as key parameters when surveilling AIS with mild curves by RS surface topography. These slides can be retrieved under Electronic Supplementary Material.