What is vertebrae S1?

Vertebra S1, or the first sacral vertebra, is the uppermost vertebra of the sacrum, a triangular bone at the base of the spine. It articulates with the lumbar vertebra L5 above and connects to the sacrum below, forming the sacroiliac joints with the ilium of the pelvis. S1 plays a crucial role in weight-bearing and stability, serving as a key structural component of the lower back and pelvis. Its anatomy includes a broad base, which helps support the upper body and transfer loads to the pelvis and legs.