The embryogenesis of congenital vertebral dislocation: Early embryonic buckling?

Congenital vertebral dislocation (CVD) is a rare congenital spinal malforma tion characterized by a translatory or rotatory vertebral displacement, or both, at a single level, that results in an abrupt angulation of the neural canal. The more caudal vertebra is dysplastic and appears at first glance to be posteriorly dislocated into the vertebral canal as a posterior hemive rtebra, but is actually well aligned with the more caudal vertebral column. Unfortunately, the present classification of complex congenital vertebral anomalies is confusing, and CVD has been grouped together with other congen ital vertebral malformations under the terms 'segmental spinal dysgenesis', 'medial spinal aplasia', and others. Moreover, a putative embryonic mechani sm has never been proposed for CVD. Based upon our experience with 6 childr en and a critical review of the literature, we identify CVD as a distinct e ntity having characteristic anatomical features. We propose a novel putativ e embryonic mechanism - early embryonic 'buckling' - which likely occurs by the 6th embryonic week, prior to the period of axonal outgrowth and the be ginning of vertebral chondrification.