Tibial hemimelia in one of the identical twins.

Tibial hemimelia, a rare congenital anomaly, is characterized by deficiency of the tibia with relatively intact fibula. The incidence of congenital deficiency of the tibia is approximately 1 per 1 million live births. The percentage of monozygotic twins is 0.8% of all newborns. Therefore, the occurrence of tibial hemimelia in monozygotic twins is 1 case per 125 million. The purpose of this article is to present a case of identical twins, in which 1 had tibial hemimelia, a double metatarsal bone and preaxial polydactyly and the other had no alterations. The patient that was affected had an anomaly in the left leg and foot. She had 7 fingers in her left foot and a left duplicated great toe. Her legs had a 3-cm difference in length, rigid inversion, adduction of feet, and severe bowing. A roentgenogram showed right tibial hemimelia with intact fibula corresponding to Jones type 3 and the first metacarpo was duplicated with a proximal osseus synostosis. Karyotyping confirmed that the twins were monozygotic. Only 1 of the identical twins had tibial hemimelia, a double metatarsal bone, and preaxial polydactyly. Congenital defects may result from aberrations in the developmental stage, the growth stage, or both. Hemimelia may result from a primary failure to form an anlage, or a primary failure to chronologically synthesize collagen. This case shows that tibial hemimelia can have variable phenotypic manifestations.