Which vertebrae are typically fused to form a solid bone structure?

The sacral vertebrae are typically fused to form a single solid structure known as the sacrum. In the development of the vertebral column, the sacral region consists of five vertebrae, which in adults become fused during early adulthood into the sacrum. This fusion provides stability and support to the pelvis and is an important connection point between the spine and the hip bones, contributing to the structure and function of the pelvic girdle. The sacrum also plays a crucial role in weight transfer between the upper body and lower limbs during activities like walking and standing.

In contrast, the cervical, thoracic, and lumbar vertebrae are encapsulated within distinct segments of the spine and remain individual vertebrae throughout adulthood, allowing for flexibility and a range of movements necessary for various motions of the neck and back.