Lumbosacral trunk

The lumbosacral trunk is a crucial component of the peripheral nervous system, linking the lumbar and sacral plexuses to facilitate motor and sensory innervation of the lower limb and pelvic region.

Origin

The trunk arises from the anterior rami of the fourth (L4) and fifth (L5) lumbar spinal nerves. Specifically, a branch from L4, known as the lumbosacral communicating nerve, joins the anterior ramus of L5 to form the lumbosacral trunk.

Course

The lumbosacral trunk descends into the pelvic cavity, positioned anterior to the sacroiliac joint. It then courses along the lateral pelvic wall, where it integrates with the anterior rami of the first four sacral nerves (S1–S4) to contribute significantly to the sacral plexus.

Branches

The lumbosacral trunk typically does not give rise to its own branches. Instead, its nerve fibers integrate into the sacral plexus, contributing to the innervation of the lower limb and pelvic structures through the branches of the sacral plexus, such as the:

• Sciatic nerve (L4-S3)

• Superior gluteal nerve (L4-S1); supplies the gluteus medius, gluteus minimus, and tensor fascia lata muscles

• Inferior gluteal nerve (L5-S2); innervates gluteus maximus muscle

• Nerve to quadratus femoris and inferior gemellus muscles (L4-S1); innervates quadratus femoris and inferior gemellus muscles

• Nerve to obturator internus and superior gemellus muscles (L5-S2); innervates obturator internus and superior gemellus muscles