One of the lowest bones in your back, the Sacrum is a large, triangular bone that connects to the base of your spine. It forms when you reach between 18 and 30 years old when your S1-S5 sacral vertebrae fuse together. It’s located at the back of your pelvic cavity, between its wings, and forms important joints with your other bones. The sacrum is a very complex bone that helps to provide support for the spine and protection for the spinal nerves, as well as articulates with your hip bones. Among the most common injuries suffered in the sacrum region is a sprain to the sacroiliac joint that articulates at the ala, or side-base projections, of the sacrum. Sacrum Articulations The sacrum articulates (forms joints) with four different bones. The first is the lowest lumbar vertebra. The second is the tailbone, which is directly below the sacrum, and the third is the hip bone at the ilium region. In humans, the sacrum is able to move slightly on its own along the sagittal plate to b...