Two-Phalanged Fifth Toe in Korean

Park, Hyung Bin; Sohn, Hyun Joon

Abstract

Except for the hallux, the human toes classically present three phalanges, distal, middle and proximal. However in 5th toe, only two phalanges are frequently observed. In this condition, known as synarthrosis of the distal interphalangeal joint, the middle and distal phalanges are fused together to appear as symphalangism or biphalangeal 5th toe. Phalanges of 5th toe was investigated in 1,187 cases of Korean radiographs. The incidence of symphalangism was found to be 74% in 1,150 adult. The bilaterality was 99%. To prove proove the genetic basis of the symphalangism, pedigree studies were performed. The symphalangism of the 5th toe was supposed to be an autosomal dominant trait. As an phenotype of recessive homozygote the triphalaneal subjects were traced to investigate their families. Pedigrees of four families in which both parents had triphalangea of 5th toe showed that their offsprings always showed the triphalangea. Therefore, it suggests the symphalangism inherit as a Mendelian dominant trait and it seems to be an example of microevolution or genetic adaptation to bipedalism.