Perineum LO9

9. Understand the location and major branches of the sacral plexus.

The sacral plexus is composed of the lumbosacral trunk, ventral rami of S1-S3, and a portion of the ventral ramus of S4. The ventral rami of the sacral spinal nerves enter the pelvic cavity through the anterior sacral foramina, and lie anterior to the piriformis mm.

The lumbosacral trunk is formed by a portion of the ventral rami of L4, L5, and S1. It is visible medial to psoas major m., and the lumbar portion joins S1 anterior to the sacro-iliac (SI) joint.

The sacral plexus has numerous branches, including superior & inferior gluteal nn., sciatic n., and pudendal n. Most branches of the sacral plexus will discussed in more detail in the musculoskeletal sequence. The pudendal n. and its branches will be discussed in more detail in this session.