The prevalence and ossification pattern of the biphalangeal and triphalangeal lateral toes

PURPOSE: Biphalangealism of the toes is an exclusively human phenomenon. The aim of this study was to evaluate the development of the lateral toes in childhood by following the ossification pattern of the phalanges. METHODS: Foot radiographs of 913 adults have been evaluated for biphalangealism of 3rd to 5th toe. The pediatric group, aged 6–15 years of age, was assessed for the number of ossification centers in the foot. RESULTS: In adults, the mean prevalence of biphalangealism in the 5th toe was 41.39%, in the 4th toe was 2.15%, and in the 3rd toe was 0.48%. In children, 45% feet had four ossification centers in the 5th toe. The epiphysis center of the middle and distal phalanx was missing. In the 4th toe, four centers were present in of 2.47% of cases. Those values are similar to the prevalence of the biphalangeal toes in adult population. The remaining toes had 5 or 6 ossification centers. In the 5-center toe, the epiphysis of the middle phalanx was missing. CONCLUSION: A missing distal phalanx epiphyseal ossification center is considered indicative of a biphalangeal toe, and the toes with 5 or 6 ossification centers are indicative of triphalangeal toes. The reason for such evolution of the lateral toes is still debated, but the differences in anatomy most likely have no impact on foot function.