Postnatal maturation of the sacrum and coccyx: MR imaging, helical CT, and conventional radiography

OBJECTIVE. The purpose of this paper is to provide a detailed radiologic description of the postnatal developmental anatomy of the sacrum and coccyx as revealed by MR imaging, helical CT, and conventional radiography. MATERIALS AND METHODS, One hundred ten imaging examinations of the sacrococcygeal spine were performed in patients who were newborn to 30 years old. Imaging included conventional radiography (n = 63), three-dimensional gradient-recalled echo MR imaging (n = 10), and helical CT with sagittal and angled coronal reformations (n = 37), A detailed analysis was performed of the ossification and fusion of the primary and secondary ossification centers. RESULTS. The sacrum and coccyx were noted to develop from 58 to 60 sacral ossification centers and eight coccygeal centers, respectively. These centers were noted to ossify and fuse in an organized temporal pattern from the fetal period to the age of 30. CONCLUSION. The sacrum and coccyx are formed by a complex process that fuses primary and secondary ossification centers. Because the maturation process can be asymmetric, an understanding of this process may prove useful for distinguishing physeal plates from fracture lines.