Femoral Nerve

Introduction

Introduction to the Femoral Nerve in the Anterior Thigh

The femoral nerve is the largest branch of the lumbar plexus, arising from the dorsal divisions of the ventral rami of L2, L3, and L4. It descends through the psoas major, emerges at its lateral border, and passes deep to the inguinal ligament into the femoral triangle. In the thigh, it supplies the anterior compartment muscles, the skin of the anterior thigh, and via its terminal branch—the saphenous nerve—the skin of the medial leg and foot. Its superficial position in the femoral triangle makes it a target for regional anaesthesia (femoral nerve block), but also renders it vulnerable to traumatic injury and iatrogenic damage during pelvic and hip surgery.

Study

1. Origin and Formation

The femoral nerve is formed within the substance of the psoas major muscle by the union of the dorsal divisions of the anterior primary rami of L2, L3, and L4. It emerges from the lateral border of the psoas major at the level of the iliac crest, then descends in the groove between the psoas major and iliacus muscles. It enters the thigh deep to the inguinal ligament, lateral to the femoral sheath, approximately halfway between the anterior superior iliac spine (ASIS) and the pubic symphysis (the mid‑inguinal point).

2. Course and Relations in the Femoral Triangle

In the femoral triangle, the femoral nerve lies lateral to the femoral artery, outside the femoral sheath. It is located on the iliopsoas muscle, covered by the fascia iliaca. The nerve almost immediately divides into an anterior division (giving muscular branches to sartorius and pectineus, and the anterior cutaneous nerves of the thigh) and a posterior division (giving muscular branches to the quadriceps femoris and the saphenous nerve). The saphenous nerve then enters the adductor canal with the femoral vessels.

The femoral nerve is relatively superficial, separated from the skin only by the fascia lata and the subcutaneous tissue. This superficial location facilitates nerve blocks and electrophysiological studies but also makes it susceptible to penetrating injuries.

3. Branches of the Femoral Nerve in the Thigh

Muscular branches (motor): The anterior division supplies the sartorius and pectineus. The posterior division supplies the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius (the quadriceps femoris).

Cutaneous branches (sensory): The anterior cutaneous nerves of the thigh (intermediate and medial cutaneous nerves) pierce the fascia lata to supply the skin over the anterior and anteromedial thigh. The saphenous nerve, the terminal sensory branch, runs through the adductor canal, gives off an infrapatellar branch to the skin over the patella, and continues to supply the skin of the medial side of the leg and the medial border of the foot as far as the first metatarsophalangeal joint.

Articular branches: Small articular twigs supply the hip and knee joints.

4. Blood Supply

The femoral nerve receives its blood supply from the lateral circumflex femoral artery, a branch of the profunda femoris artery. The vessels enter the nerve along its epineurium.

5. Clinical Relevance

Femoral nerve block: A common regional anaesthetic technique for knee surgery, hip fractures, and anterior thigh procedures. The nerve is targeted in the femoral triangle under ultrasound guidance.

Femoral neuropathy: Injury to the femoral nerve results in weakness of knee extension (quadriceps paralysis) and loss of sensation over the anterior thigh and medial leg/foot. The patellar tendon reflex is absent. Causes include trauma, pelvic fractures, hip surgery (particularly anterior approaches), haematoma, diabetic amyotrophy, and retroperitoneal tumours.

Saphenous nerve entrapment: The saphenous nerve can be compressed as it exits the adductor canal, causing medial knee and leg pain (saphenous neuritis). It may also be injured during saphenous vein harvesting or knee arthroscopy.

Iatrogenic injury: The femoral nerve is at risk during pelvic lymph node dissection, renal transplantation, and total hip arthroplasty (especially the anterior approach).

Summary

Summary of the Femoral Nerve in the Anterior Thigh

The femoral nerve (L2–L4) supplies the muscles of the anterior thigh (quadriceps, sartorius, pectineus) and provides sensory innervation via the anterior cutaneous nerves of the thigh and the saphenous nerve. It lies lateral to the femoral artery in the femoral triangle. Injury leads to loss of knee extension, absent knee jerk, and sensory loss over the anteromedial thigh and medial leg. The nerve is important for regional anaesthesia and is vulnerable during pelvic and hip surgery.