Accessory ossification centres at the thoracolumbar junction.

A survey of 810 thoracolumbar junction CT scans demonstrated several forms of accessory ossification centres and vestigial ribs associated with the posterior element processes. Four examples of short T12 ribs and 15 L1 ribs were identified, in addition to 8 accessory ossification centres at L1, and 3 at T12. Radiographic features of accessory ossification centres were compared with histologic characteristics from cadaver studies. Accessory ossification centres have occasional clinical significance when they may be confused with fractures at the thoracolumbar junction. Differential diagnosis relies on adequate visualization of their cortical margins to distinguish them from recent fractures of the processes.