What is a transitional vertebra?
A transitional vertebra occurs when a vertebra at the junction between spinal morphological segments has features of both segments.
A C7 vertebral body with cervical ribs, an L1 vertebral body with ribs, and an L5 vertebra with transverse processes that partially or completely fuse to the sacrum represent cervicothoracic, thoracolumbar, and lumbosacral transitional vertebrae, respectively.
Of these, lumbosacral transitional vertebrae are most common.