A sequential developmental field defect of the vertebrae, ribs, and sternum, in a young woman of the 12th century AD

Changes in the vertebral column are often noted in skeletal material. Descr iptions of these anomalies are often lacking, and their developmental origi ns are not often discussed. The skeleton of a young woman from the medieval cemetery of Tirup, in Denmark, has multiple defects of the axial skeleton, including extra thoracic and lumbar vertebrae, border shifting, extra ribs , block vertebra, and deformed sternum. This case study is particularly int eresting because of the number and diversity of anomalies seen; the rarity of these defects, even in living populations; and her survival to adult age . Careful analysis of the bones and use of the morphogenetic method of dete rmining development stages has led to the conclusion that the initial defec t probably occurred very early in development, during blastogenesis, with t he initial development of at least two extra somitomeres in the paraxial me soderm. These extra elements in turn led to problems in union and different iation, and later chondrification and ossification of the vertebra. The mal formations of the vertebrae also induced changes in the ribs and sternum. T he initial error of segmentation is identified as a developmental field def ect, and the cascade of anomalies seen is a developmental sequence caused b y the initial field defect. The genetic and environmental causes of develop mental field defects are reviewed. (C) 2000 Wiley-Liss, Inc.