Vertebral body underdevelopment

The sacrum (plural: sacra or sacrums), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of sacral vertebrae S1–S5 between 18 and 30 years of age.The sacrum situates at the upper, back part of the pelvic cavity, between the two wings of the pelvis. It forms joints with four other bones. [Source: Wikipedia ]

May Cause
Round vertebrae