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 radiolog ic description of the postnatal developmental anatomy of the sacrum an d coccyx as revealed by MR imaging, helical CT, and conventional radio graphy. 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), t hree-dimensional gradient-recalled echo MR imaging (n = 10), and helic al CT with sagittal and angled coronal reformations (n = 37), A detail ed analysis was performed of the ossification and fusion of the primar y and secondary ossification centers. RESULTS. The sacrum and coccyx w ere noted to develop from 58 to 60 sacral ossification centers and eig ht coccygeal centers, respectively. These centers were noted to ossify and fuse in an organized temporal pattern from the fetal period to th e age of 30. CONCLUSION. The sacrum and coccyx are formed by a complex process that fuses primary and secondary ossification centers. Becaus e the maturation process can be asymmetric, an understanding of this p rocess may prove useful for distinguishing physeal plates from fractur e lines.