Comparison of the degree of pes planovalgus and muscle mass of the ankle joint and foot muscles between children with Down syndrome and children with typical development.

We aimed to compare the degree of pes planovalgus and muscle mass of the ankle joint and foot muscles between children with Down syndrome (DS) and children with typical development (TD). We also examined the association of the degree of pes planovalgus with muscle mass of the ankle joint and foot muscles in children with DS and children with TD. The subjects were 24 children with TD (control [CTR] group) and 23 children with DS (DS group). To assess pes planovalgus, the Arch Height Index (AHI) in the standing position was measured. Muscle thickness of the ankle joint and foot muscles was measured using an ultrasound imaging device. The AHI and thickness of the soleus and tibialis posterior muscles were significantly lower in the DS group than those in the CTR group. The thickness of the flexor digitorum longus muscle was significantly greater in the DS group than that in the CTR group. Stepwise regression analysis revealed that the thickness of the flexor digitorum longus muscle was a significant and independent factor of the AHI in children comprising the CTR and DS groups. The thickness of the flexor digitorum longus muscle increased with decreasing AHI. The results of this study suggest that the AHI and muscle mass of the soleus and tibialis posterior muscles decrease, while muscle mass of the flexor digitorum longus muscle increases in children with DS. The results also indicate that decreased AHI is associated with increased muscle mass of the flexor digitorum longus muscle in children.