How many bones form the sacrum?

How many bones form the sacrum?

• A. 4
• B. 5
• C. 6
• D. 7

Answer: (B)

Five vertebrae fuse to form the sacrum. At birth these segments are separate, and during growth they gradually unite into one bone, typically completing this fusion by late adolescence. The sacrum then sits at the base of the spine, forming the back wall of the pelvic cavity and helping transmit weight to the pelvis. The standard count is five because that fusion gives a single, stable bone, though rare variations can involve incomplete or additional fusion with neighboring levels, they don’t change the usual idea that the sacrum is produced by five fused segments.

Five vertebrae fuse to form the sacrum. At birth these segments are separate, and during growth they gradually unite into one bone, typically completing this fusion by late adolescence. The sacrum then sits at the base of the spine, forming the back wall of the pelvic cavity and helping transmit weight to the pelvis. The standard count is five because that fusion gives a single, stable bone, though rare variations can involve incomplete or additional fusion with neighboring levels, they don’t change the usual idea that the sacrum is produced by five fused segments.