The sacrum performs few active roles in the human body, primarily supporting the rest of the human spine. The sacrum exists at the end of the spinal column, appearing as a triangular bone. It rests in the c-shape portion of the lower back, connecting the lumbar vertebrae with the pelvis.
In addition to providing support, the sacrum works in coordination with the rest of the human spine, which provides movement and flexibility. According to the Mayfield Clinic, the primary role of the sacrum is one of a bridge, as it connects the hipbones, or the iliac crest, with the rest of the spine. The sacrum forms a long triangular shape, which derives from five connecting vertebrae. These vertebrae combine with the iliac bones along the sides, which form the pelvic girdle. Just above the sacrum is the lumbar spine, also called the lower spine. This section of the spinal cord forms from five discs, named L1 through L5. These discs, although small, support the weight of virtually the entire human body. Just above the lumbar spine is the thoracic spine. This portion of the spine surrounds and protects the heart and lungs. It also forms the rib cage, and offers little movement and flexibility.