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Roll-over shapes of the ankle-foot and knee-ankle-foot systems of able-bodied children

Hansen, A.H. and Meier, M.R. (2010) Roll-over shapes of the ankle-foot and knee-ankle-foot systems of able-bodied children. Clinical Biomechanics, 25 (3). pp. 248-255. ISSN 0268-0033

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Abstract

Background: The roll-over shape is the effective rocker shape that a lower limb system conforms to during a step. The roll-over shape concept has been explored in detail in adults and has been successfully used in the design, evaluation, and alignment of lower limb prostheses and orthoses. No such analysis exists for the pediatric population. Therefore, the purpose of this study was to investigate the ankle-foot and knee-ankle-foot roll-over shapes in able-bodied children, values that could serve as tools for design and evaluation of lower limb pediatric prostheses and orthoses. Methods: This study describes a multi-center retrospective review of existing motion analysis data (n = 153 from three centers). Roll-over shapes were calculated by transforming center of pressure data from a laboratory-based coordinate system into two body-based coordinate systems. Roll-over shapes were then characterized using a circular arc model. Best-fit radii of roll-over shapes for children in three age groups (3-7 years, 8-11 years, and 12-17 years) were compared using the Kruskal-Wallis Test. Findings: No significant changes were found in roll-over shape radii between the three age groups (p = 0.54 for ankle-foot roll-over shape radii; p = 0.12 for knee-ankle-foot roll-over shape radii). The weighted mean of median radii for ankle-foot and knee-ankle-foot roll-over shapes from the three centers were approximately 22% and 17% of body stature, values similar to those seen in adults. Interpretation: Children produce nearly circular knee-ankle-foot roll-over shapes at a young age that are similar to those seen in adults when scaled by body stature. Keywords: foot, ankle, knee, rocker, cam, center of pressure, prosthetics