Lumbar Plexus

Q: What symptoms occur with femoral nerve damage?

Femoral nerve lesions may present with: Motor deficits: inability to extend the knee joint; compression under the inguinal ligament causes quadriceps paresis. Advanced cases may show partial weakness in hip flexion.Sensory deficits: anesthesia over the anterior thigh and medial leg; prominent sensory loss in the anteromedial area of the lower limb.Reflex changes: diminished or absent patellar (knee-jerk) reflex.Pain: compression under the inguinal ligament can cause pain, tenderness upon palpation at the midpoint of the inguinal ligament, and a positive Tinel sign.

Plexus lumbalis

For medical students2 min readUpdated 2026-10-10

The lumbar plexus is a key neural network formed by the anterior rami of spinal nerves. It provides innervation to the lower anterior abdominal wall, the inguinal region, and a major portion of the lower limb skin.

LocationLocated within the substance of the m. psoas major, anterior to the transverse processes

SegmentsFormed by nerve roots from T12 to L4

FunctionProvides cutaneous innervation to the thigh, leg, and inguinal region

Topography and Upper Branches

Anatomically, the lumbar plexus is located within the substance of the psoas major muscle (m. psoas major), positioned directly anterior to the transverse processes of the lumbar vertebrae. The nerves originating from its upper segments innervate the lower trunk and inguinal region.

These include the iliohypogastric nerve (n. iliohypogastricus, segments T12–L1), which divides into two primary branches:

Lateral cutaneous branch (r. cutaneus lateralis) — heads to the skin of the superolateral gluteal region.
Anterior cutaneous branch (r. cutaneus anterior) — provides cutaneous sensation to the skin of the lower anterior abdominal wall above the pubis.

Next is the ilioinguinal nerve (n. ilioinguinalis, L1). Its sensory area includes the skin of the pubic region and the upper medial surface of the thigh. In addition, it innervates the anterior parts of the scrotum in males and the labia majora in females.

Genitofemoral Nerve

The genitofemoral nerve (n. genitofemoralis, L1–L2) features a distinct topographic course: it passes directly through or on the surface of the m. psoas major, where it divides into two functional branches:

Femoral branch (r. femoralis) — descends into the thigh, giving off branches to the skin over the femoral triangle.
Genital branch (r. genitalis) — courses toward the inguinal region. In males, it innervates the skin of the scrotum and spermatic cord, while in females, it provides sensory innervation to the skin of the inguinal canal.

Nerves of the Lower Limb

The lower segments of the plexus form larger nerves that descend into the thigh and leg.

Lateral cutaneous nerve of the thigh (n. cutaneus femoris lateralis, L2–L3). This nerve exits the pelvic cavity near the anterior superior iliac spine (spina iliaca anterior superior) and passes under the inguinal ligament. Its function is to innervate the skin of the anterolateral thigh.
Femoral nerve (n. femoralis, L2–L4). It gives off anterior cutaneous branches of the thigh (rr. cutanei anteriores) supplying the anterior surface of the thigh. Its longest branch, the saphenous nerve (n. saphenus), descends further to innervate the skin of the medial aspect of the leg and the medial border of the foot.
Obturator nerve (n. obturatorius, L2–L4). It gives off an inconstant cutaneous branch that supplies the skin of the medial thigh.

Frequently asked questions

Which spinal nerve roots form the lumbar plexus?

The lumbar plexus is formed by the anterior rami of spinal nerves, including the subcostal nerve (T₁₂), iliohypogastric nerve (T₁₂–L₁), ilioinguinal nerve (L₁), genitofemoral nerve (L₁–L₂), lateral cutaneous nerve of the thigh (L₂–L₃), femoral nerve (L₂–L₄), and obturator nerve (L₂–L₄).

Which muscles are innervated by branches of the lumbar plexus?

Branches of the lumbar plexus contribute to the innervation of the following muscles:

Psoas minor muscle (m. psoas minor) — innervated directly from the plexus lumbalis (L₁–L₂).
Abdominal wall muscles — receive innervation via the subcostal, iliohypogastric, and ilioinguinal nerves.
Vastus lateralis and vastus medialis muscles (m. vastus lateralis, m. vastus medialis) and tibialis anterior muscle (m. tibialis anterior) — serve as key indicator muscles for the L₄ nerve root.

What symptoms occur with femoral nerve damage?

Femoral nerve lesions may present with:

Motor deficits: inability to extend the knee joint; compression under the inguinal ligament causes quadriceps paresis. Advanced cases may show partial weakness in hip flexion.
Sensory deficits: anesthesia over the anterior thigh and medial leg; prominent sensory loss in the anteromedial area of the lower limb.
Reflex changes: diminished or absent patellar (knee-jerk) reflex.
Pain: compression under the inguinal ligament can cause pain, tenderness upon palpation at the midpoint of the inguinal ligament, and a positive Tinel sign.

Where is the lumbar plexus located?

The plexus is embedded within the substance of the psoas major muscle (m. psoas major), anterior to the transverse processes of the lumbar vertebrae.

What branches arise from the genitofemoral nerve?

It divides into a femoral branch (supplying the skin of the femoral triangle) and a genital branch (supplying the scrotum and spermatic cord in males, or the skin of the inguinal canal in females).

Which nerve exits the pelvis near the spina iliaca anterior superior?

The lateral cutaneous nerve of the thigh (n. cutaneus femoris lateralis) exits the pelvis near the anterior superior iliac spine.

Go deeper

Topography of the branches of the iliohypogastric nerve
Innervation zones of the ilioinguinal nerve
Division of the genitofemoral nerve within the psoas major
Course of the lateral cutaneous nerve of the thigh under the inguinal ligament
Cutaneous branches of the femoral and obturator nerves