Anterior rami of lumbar nerves

1. Origin

The anterior rami of lumbar nerves (L1–L5) arise from the lumbar spinal nerves once these nerves exit the intervertebral foramina. They branch extensively to provide motor and sensory innervation to the lower limb, abdominal wall, and parts of the pelvis.

2. Direct Muscular Branches

Some of the branches from the anterior rami directly innervate muscles of the body wall, such as:

• Iliacus (L2, L3)

• Quadratus lumborum (T12 to L4)

3. Lumbar Plexus Formation

The anterior rami of lumbar nerves L1–L5 traverse the psoas major muscle, during which the following occurs:

• L1–L3 anterior rami, along with minor contributions from L4 (from below) and T12 subcostal nerve (from above), form the lumbar plexus.

• The lumbar plexus provides motor and sensory innervation to the abdominal wall, lower limb, and external genitalia.

Divisions

• L2–L4 anterior rami: Each splits into ventral and dorsal branches.

• L1 anterior ramus: Forms only a ventral branch, with no dorsal division.

Key Nerves Derived from the Anterior Rami

• L1 anterior ramus: Gives rise to the iliohypogastric and ilioinguinal nerves.

• L1–L2 anterior rami: Form the genitofemoral nerve.

• L2–L4 ventral branches: Contribute to the obturator nerve, which innervates the adductor muscles.

• L2–L4 dorsal branches: Form the femoral nerve, responsible for motor innervation to the anterior thigh.

• L2–L3 posterior divisions: Give rise to the lateral femoral cutaneous nerve, which provides sensory innervation to the lateral thigh.

4. Lumbosacral Trunk and Sacral Plexus

• The L4 anterior ramus (lower portion) and the L5 anterior ramus join together to form the lumbosacral trunk.

• The lumbosacral trunk then descends into the pelvic region and joins with sacral anterior rami, forming the sacral plexus, which provides motor and sensory innervation to the gluteal and lower limb regions.

Key Branches of the Sacral Plexus

• Superior gluteal nerve: L4–S1

• Inferior gluteal nerve: L5–S2

• Nerve to quadratus femoris: L4–S1

• Nerve to obturator internus: L5–S2

• Sciatic nerve: L4–S3

5. Clinical Relevance

Compression, trauma, or damage to the anterior rami (e.g., from lumbar disc herniation) can impair the lumbar plexus, causing muscle weakness, sensory deficits and/or pain in affected areas of the lower limbs.