Development, validation, and psychometric analysis of Foot and Ankle Flexibility Index (FAFI)

Aim: To develop a new tool for identifying joint hypermobility of the paediatric foot and ankle, based on a dichotomous scoring system utilising the Lower Limb Assessment Score (LLAS), to separate the foot and ankle items. Material and methods: A total of 205 children, aged between 5 and 10 years, participated in a cross-sectional study. The new tool Foot and Ankle Flexibility Index (FAFI) was predicated upon the last 7 items of LLAS, which are specific to the foot and ankle. The internal consistency was measured with Cronbach's test. Kappa statistics with 95% CI were calculated to verify the level of inter-rater and intra-rater agreement for the FAFI. Results: Cronbach's alpha returned 0.82. The correlations between items returned a mean of 0.59 (range: 0.43–0.74). The discrimination score on the ROC curve (4 points) showed that the model can be used to identify children with joint hypermobility of the foot and ankle. Inter-rater reliability was largely good (ICC = 0.89). Excellent intra-rater reliability was found (ICC = 0.96) Conclusions: This study identified high reliability between evaluators, and high sensitivity and specificity, for a new reliable and valid tool for the identification of foot and ankle joint hypermobility.