How are sacral vertebrae best described?

• A. Not fused together
• B. Partially fused
• C. Fused as a single unit
• D. Fused together

Answer: (D)

The main idea is that the sacral vertebrae become one bone. In humans, five sacral vertebrae typically fuse during development to form a single bone called the sacrum. This fusion creates one sturdy structure at the base of the spine that transfers weight to the pelvis and forms part of the posterior pelvic wall. Because of this, they are described as fused together. If they were not fused or only partially fused, you would still see separate vertebrae, which isn’t how the adult sacrum is. The notion of being fused into a single unit conveys the same outcome, but the standard description is that they are fused together into one bone.