Case presentation of calcaneonavicular coalition in monozygotic twins

A case study of monozygotic twins with bilateral calcaneonavicular coalitions is presented. With the frequency of tarsal coalitions being approximately 1% to 2% and the frequency of monozygotic twins being 0.4%, it is a rare but predictable finding to see monozygotic twins with tarsal coalitions. This sheds additional light on the etiology of tarsal coalition that historically has been believed to be a defect in mesenchymal differentiation with indications of a genetic component. Despite the limited number of subjects used for various studies, tarsal coalitions have been considered to be an autosomal dominant defect with variable penetrance. In fact, inheritance of tarsal coalitions is more complicated than simple mendelian inheritance patterns and is likely to be a single error in a polygenic system. Because of this inheritance pattern, it is important to consider evaluating siblings and close family members of patients diagnosed with a tarsal coalition.