How many vertebrae make up the sacrum?

How many vertebrae make up the sacrum?

• A. 5 vertebrae
• B. 4 vertebrae
• C. 6 vertebrae
• D. 7 vertebrae

Answer: (A)

The sacrum is formed by five vertebral segments that fuse into a single bone. These segments—S1 through S5—typically fuse during adolescence to adulthood, resulting in one triangular bone at the base of the spine. In standard anatomy, the sacrum thus counts as five vertebrae. This fused structure supports and transmits weight to the pelvis and forms the sacroiliac joints with the ilia. So, five is the correct number. Variations like sacralization or lumbarization can alter how many segments are recognizable, but the usual adult sacrum consists of five fused vertebrae.

The sacrum is formed by five vertebral segments that fuse into a single bone. These segments—S1 through S5—typically fuse during adolescence to adulthood, resulting in one triangular bone at the base of the spine. In standard anatomy, the sacrum thus counts as five vertebrae. This fused structure supports and transmits weight to the pelvis and forms the sacroiliac joints with the ilia. So, five is the correct number. Variations like sacralization or lumbarization can alter how many segments are recognizable, but the usual adult sacrum consists of five fused vertebrae.