Radiology of postnatal skeletal development. XI. The first cervical vertebra.

Forty-four first cervical vertebra were removed from cadavers and skeletons ranging in age from full-term neonates to 14 years. These were studied roentgenographically to duplicate antero-posterior and transverse appearances without superimposition of the skull or other vertebra. Ossification was present in both posterior (neural) arches at birth. These ossification centers extended toward the rudimentary spinous process to form the posterior synchondrosis. Each also extended anteriorly into the articular facet region. The posterior ossification centers formed all the bone present in the facets. Anteromedial to each facet a neurocentral synchondrosis formed on each side of the expanding anterior ossification center. The anterior ossification center appeared between six months and two years. Normally a single center formed. However anterior ossification was some-times multifocal. Infrequently the posterior centers extended into the anterior arch and met as a single anterior synchondrosis. By four to six years the posterior synchondrosis and the anterior neurocentral synchondroses were fused. All three synchondroses fused at approximately the same time, although the posterior one often slightly preceded the anterior ones. Accordingly, the spinal canal of C1 reached maximum size at this stage of development. Further growth was then limited to periosteal addition on the external surface, leading to thickening and increased height, but without significantly altering the size of the spinal canal.