Anatomy
At birth, there are 5 (usually) distinct sacral bones; fusion starts age 16-18, finished about 34. S1 is the top (i.e. base) and biggest segment of the fused sacrum. Consists of broad, expanded large body in front of triangular sacral canal, foramina either side at bottom, ridge where fused with S2.
Clinical
Articulates with L5 above through fibrocartilaginous disc, ilium each side.
Interested in taking our award-winning Pocket Anatomy app for a test drive?
