The sacrum is the triangular bone
at the bottom of the spine that joins with the hip bones to make up the bony pelvis.
They compared measurements of its lumbar vertebrae (lower back) and sacrum (a triangular bone
at the base of the spine) to those of modern humans, fossil hominins (extinct bipedal human ancestors), and a sample of mammals that commonly move around in trees, including apes, sloths and an extinct lemur.
The scan revealed a well-corticated, triangular bone
posterior to the talus.
My pelvis was broken in two places and I also damaged the sacrum, a large triangular bone
at the base of the spine which meets the pelvis, and it is all a bit close to the internal organs, but fortunately there was nothing damaged which is very good in some respects.
Blood felt some pain in her lower back, and a subsequent MRI revealed that she had a stress fracture in her sacrum, a large, triangular bone
at the base of her spine.