Joint hypermobility and preschool-age flexible flatfoot

Flexible flatfoot is the most common condition seen in pediatric orthopedic practice and generalized joint hypermobility is widely regarded as one of the predisposing factors. However, in previous studies, the flatfoot was defined by observers' subjective evaluation of the eversion of the bare foot in the standing position; and the joint hypermobility was defined by the Beighton score. The objective of this study is to evaluate the correlation between preschool-age flexible flatfoot and joint hypermobility in preschool-age children objectively. Footprints were measured on a Harris and Beath footprint mat. Flatfoot flexibility was assessed by Staheli Plantar Arch Index (PAI). Other than the Beighton score, 2 new measurement methods, the thumb-to-forearm test and the thumb-thrust test were developed to evaluate joint hypermobility. Of the 291 preschool children from 4 different kindergarten schools included in this study, 156 were boys and 135 were girls. The mean age was 64.18 ± 9.33 months (range 35-88 months). Pearson correlation analysis demonstrated PAI was not associated with the Beighton score (R = 0.020, P = .735), thumb-to-forearm grade (R = 0.109, P = .066), and thumb-thrust grade (R = 0.027, P = .642). Two-sample t-test results showed that the normal and flatfoot groups did not differ significantly in the Beighton score (P = .404), thumb-to-forearm grade (P = .063), and thumb-thrust grade (P = .449). The results demonstrated no correlation between joint hypermobility and preschool-age flexible flatfoot when flatfoot was defined with Staheli PAI and joint hypermobility with the Beighton score. Even with 2 new methods, the thumb-to-forearm test and thumb-thrust test, to define joint hypermobility, we still found no correlation between preschool-age flexible flatfoot and joint hypermobility.