Posterior Ramus of First Sacral Nerve (Right)

Origin

The posterior ramus of first sacral nerve originates as one of two terminal branches of the first sacral nerve, the other being the anterior ramus.

Course

The posterior ramus of first sacral nerve emerges from the posterior sacral foramen. As it exits, it is covered by the multifidus muscle and divides into medial and lateral branches. At lower sacral levels (S2-S4), the posterior sacral rami diminish in size.

Branches

The medial branch is small and terminates in the multifidus muscle.

The lateral branch joins with branches of the fifth lumbar nerve (L5) and all other posterior sacral rami to form loops posterior to the sacrum. Branches from these loops run posterior to the sacrotuberous ligament and form a second series of loops under gluteus maximus. Two or three gluteal branches arise here and pierce the gluteus maximus (along a line from the posterior superior iliac spine to the coccygeal apex) to innervate the posterior gluteal skin.

Supplied Structures & Function

The medial branch supplies motor innervation to the multifidus muscle. The lateral branch supplies sensory innervation to the posterior gluteal skin (middle cluneal nerve).