What is the sacrum?

The sacrum is indeed the bottom-most segment of the spine, composed of five fused vertebrae. This anatomical structure sits directly above the coccyx (tailbone) and below the lumbar vertebrae. The sacrum plays a critical role in the skeletal system as it forms the posterior part of the pelvis and provides support for the upper body when standing and walking. Additionally, it serves as an essential site for muscle attachment and is involved in the structure of the pelvis, including the sacroiliac joints that connect it to the hip bones.

Recognizing the sacrum's role as a segment made up of fused bones highlights its stability and importance in distributing weight and providing strength to the pelvic girdle, which is not something that muscle or joints inherently offer in the same manner. Understanding these aspects of the sacrum is vital for a comprehensive knowledge of human anatomy and its function in sports medicine.