Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Longitudinal Failure of Upper-Limb Formation*†

Abstract

Failure of formation of the structures of the upper extremity presents as longitudinal or transverse deficiencies of the embryonic limb bud. The deficiencies that develop along longitudinal axes are classified as radial, central, or ulnar. Use of the once commonly employed terms pre-axial and post-axial for describing longitudinal deficiencies is discouraged as these terms do not include the concept of central defects. It is tempting to speculate that these axially oriented failures of formation are the result of teratogenic insults or genetic influences that destroy cells at specific locations on the apical ectodermal ridge or the supporting mesoderm of the embryonic limb bud7. Although this is true for radial deficiencies, which characteristically affect only the structures on the radial border of the forearm and hand, the cause of ulnar and central deficiencies is not as clearly defined. Ulnar deficiency may include dysplasia of the thumb and the radial rays in addition to the ulnar structures. Central deficiency (cleft hand) is frequently associated with polydactyly (duplication) or syndactyly (failure of differentiation), or both, of the central digits. These more complex presentations suggest that the concept that deficiencies of the upper extremity are related to focal limb-bud-cell destruction is too simplistic. Nevertheless, it provides a basis for categorizing and discussing the clinical presentations. Radial deficiency describes a spectrum of osseous, musculotendinous, and neuromuscular dysplasias of the radial border of the upper limb69. Kato et al.35 produced varying degrees of radial deficiency by administering Myleran (busulfan) to pregnant WKAH/Hkm rats at nine to 11.5 days of gestation. The extent of the deficiencies was dose-related and resembled that of deficiencies seen in humans. Associated skeletal, hematological, cardiac, renal, and gastrointestinal defects24,27,28,32,71,79,87 may be overlooked initially because …