Abstract
The embryonic chick wing has been used extensively in experimental analyses of the mechanisms involved in limb development. This study employs the embryonic wing in an examination of the possible origin of congential pseudoarthrosis, a poorly understood limb disorder. To this end, chick radii were fractured in the middiaphysis prior to the onset of osteogenesis (6.5β7 days of incubation). The subsequent development of the fractured elements was examined using both whole mount preparations and histology. Callus cartilage did not form around any of the fractures. Nonetheless, the majority (29 of 33 specimens) of fractures united during primary osteogenesis (within 24β36 h of the operation), with bone formation occurring both across the fracture site and also over the cut ends of the cartilage. In addition, bones that exhibited a configuration, similar to that described as giving rise to a type II congenital pseudoarthrotic condition were obtained. Typically, these bones showed an βhourglassβ constriction midshaft and anterior bowing. These results suggest that the embryonic chick limb may serve as a useful experimental model system for the investigation of this congenital limb disorder.