Anatomic and etiological classification of congenital limb deficiencies.

Limb deficiencies, the congenital absence or hypoplasia of a long bone and/or digits, vary greatly in their anatomy and etiology. Previous attempts to classify the range of possible phenotypes have not included all types of deficiencies. We present a new classification system, which includes all potential phenotypes. Infants with limb deficiencies were identified in the hospital-based Active Malformations Surveillance Program at Brigham and Women's Hospital in Boston, MA from the years 1972 to 1974 and 1979 to 2000. Affected infants were classified based on the anatomy and apparent cause of their deficiencies. The prevalence rate of all types of limb deficiency was 0.79/1,000. Upper limb deficiencies were significantly more common than lower limb deficiencies. There was no significant difference in frequencies between deficiencies on the left and right sides of the body. Longitudinal defects were more common than terminal transverse defects; intercalary defects were uncommon. Longitudinal defects were most likely to occur on the preaxial side of the limb. Almost half of affected infants had affected digits, with normal long bones. The most common apparent cause of limb deficiencies was vascular disruption defects (0.22/1,000), such as amniotic band-related limb deficiency. This new classification system includes deficiency of each long bone, as well as absence of any finger or toe. This system will make it possible to establish the prevalence of each specific phenotype. The large number of distinct apparent causes illustrates the marked etiologic heterogeneity of limb deficiencies.