title: Flatfoot diagnosis by a unique bimodal distribution of footprint index in children.
abstract: BACKGROUND
  More than 1000 scientific papers have been devoted to flatfoot issue. However, a bimodal distribution of flatfoot indices in school-aged children has never been discovered. The purposes of this study were to establish a new classification of flatfoot by characteristic in frequency distribution of footprint index and to endue the classification with discrepancy in physical fitness.
  
  
  RESULTS
  In a longitudinal survey of physical fitness and body structure, weight bearing footprints and 3 physical fitness related tests were measured in 1228 school-aged children. Frequency distribution of initial data was tested by Kolmogorov-Smirnov test for normality and a unique bimodal distribution of footprint index was identified. The frequency distribution of footprint index manifests two distinct modes, flatfoot and non-flatfoot, by deconvolution and bootstrapping procedures. A constant intersection value of 1.0 in Staheli's arch index and 0.6 in Chippaux-Smirak index could distinguish the two modes of children, and the value was constant in different age, sex, and weight status. The performance of the one leg balance was inferior in flatfoot girls (median, 4.0 seconds in flatfoot girls vs. 4.3 seconds in non-flatfoot girls, p = 0.04, 95% CI 0.404-0.484).
  
  
  CONCLUSIONS
  The natural bimodality lends itself to a flatfoot classification. Bimodality suggests development of the child's foot arch would be a leap from one state to another, rather than a continuous growth as body height and weight. The underlying dynamics of the human foot arch and motor development will trigger research prospects.
authors.affiliation: Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei, Taiwan; Department of Pediatric Orthopedics, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Chia-Hsieh
authors.initials: CH
authors.lastname: Chang
authors.affiliation: Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Yu-Chen
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Taipei Chengshih University of Science and Technology, Taipei, Taiwan.
authors.forename: Wen-Tien
authors.initials: WT
authors.lastname: Yang
authors.affiliation: Department of Pediatric Orthopedics, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Pei-Chi
authors.initials: PC
authors.lastname: Ho
authors.affiliation: Graduate Institute of Early Intervention, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Ai-Wen
authors.initials: AW
authors.lastname: Hwang
authors.affiliation: Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Chien-Hung
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Department of Physical Education, National Taiwan Normal University, Taipei, Taiwan.
authors.forename: Jia-Hao
authors.initials: JH
authors.lastname: Chang
authors.affiliation: Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Liang-Wey
authors.initials: LW
authors.lastname: Chang
mesh_terms: D000886:Anthropometry; D002648:Child; D005260:Female; D005413:Flatfoot / Q000145:classification / Q000175:diagnosis*; D005528:Foot / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008297:Male; D010809:Physical Fitness / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D016474:Weight-Bearing