Supernumerary and absent limbs and digits of the lower limb: a review of the literature.

Anatomical history over centuries includes description of a wide variety of malformations involving the lower limbs. This article offers an organized review of these diverse abnormalities, including new understanding of mechanisms through recent discoveries in genetics and molecular biology. In 19th century Europe, a number of unique anomalies were reported, as well as evidence of foot amputations occurring in ancient Peruvian culture. Embryologically, the limbs develop early, with the lower limb being recognizable for the first time at stage 13 of development. By stage 23, the toes are clearly defined and by birth, although the legs appear bowed, the tibia and fibula are straight. Removal of the apical ectodermal ridge results in cessation of limb development, conversely, a second apical ectodermal ridge results in duplication of distal structures. Supernumerary limbs have been documented to occur as part of a teratoma with unique morphology and accompanying blood supply. Additionally, many examples of polydactyly occur in the foot postulating that deletion of chromosome 22q11 is involved in postaxial polydactyly. Such deletions occur near the middle of the chromosome at a location designated q11.2 (i.e., on the long arm of one of the pair of chromosomes 22) and this syndrome is also referred to as DiGeorge syndrome, which has a prevalence estimated at 1:4,000. Absence of the lower limbs has also been noted, with hypoplasia of the fibula being the most common manifestation of congenital bone absences in the lower limb. In addition to fibular aplasia, cases of tibial aplasia have been reported. This article is important for surgeons attempting correctional repair of lower limb anomalies, as well as providing analysis of the historical, anatomical and clinical aspects of supernumerary and absent limbs and digits for the lower limb.