Congenital kyphosis by segmentation defect: etiologic and pathogenic studies.

Sixteen cases of type II congenital kyphosis were reviewed. As a working hypothesis, we assumed that this pathology should have a behavior similar to scoliosis due to a segmentation defect, if a true unsegmented bar existed. The analysis of different parameters including the number of levels involved, the patient's age, the degree of disc space involvement, and the site of deformity did not confirm this hypothesis. Furthermore, an experimental animal study failed to reproduce this congenital anomaly. It is our belief that kyphosis resulting from a "segmentation defect" represents a developmental defect of the perivertebral structures including the annulus fibrosus, the ring apophysis, and the anterior longitudinal ligament rather than a true intervertebral bar.