Spinous process of sacrum

The spinous process of the sacrum is not an official term of Terrminologia Anatomica and refers to the rudimentary spinous processes of the five fused sacral vertebrae. In the adult human sacrum, these spinous processes fuse together along the dorsal midline to form the median sacral crest (crista sacralis mediana), a series of three to four tubercles that represent the vestigial remnants of the individual sacral spinous processes.

The S1 spinous process is the most prominent a with a mean anteroposterior length of approximately 11.6 mm and a craniocaudal height of approximately 23.1 mm.