Femoral nerve

At a glance

English

Femoral nerve

Latin (TA2)

Nervus femoralis

System

Nerve

Region

Lower limb

Side

Paired, left and right

About the femoral nerve

The femoral nerve is the chief nerve of the front, extensor compartment of the thigh. It forms within psoas major from the posterior divisions of L2, L3 and L4 ventral rami, and appears at the lateral border of that muscle low in the abdomen. It then runs down in the gutter between psoas and iliacus, behind the iliac fascia, and gives twigs to iliacus on the way.

It reaches the thigh behind the inguinal ligament, in the muscular compartment rather than inside the femoral sheath, so in the femoral triangle it sits a little lateral to the femoral artery. The usual order from lateral to medial is nerve, artery, vein and then the femoral canal with its lymphatics. Only a few centimetres below the ligament the nerve fans out into a spray of branches, conventionally grouped as an anterior division and a posterior division, with the lateral circumflex femoral artery passing between them.

The nerve to pectineus arises just above the ligament and runs behind the femoral sheath to that muscle. The anterior division supplies sartorius and gives the intermediate and medial cutaneous nerves of the thigh to the skin of the front and inner thigh. The posterior division supplies rectus femoris, vastus lateralis, vastus intermedius and vastus medialis, and through the nerve to vastus intermedius the small articularis genus. Its one cutaneous branch is the saphenous nerve, which continues to the inner leg and foot. The nerve to rectus femoris also sends fibres to the hip, and the nerves to the vasti reach the knee; the branch to vastus medialis is notably thick because it carries many sensory fibres from the knee, an example of Hilton's law. Fine twigs also reach the femoral artery.

Injury, for instance from a pelvic haematoma, retractors in abdominal or pelvic surgery, or a hip operation, weakens knee extension, removes the knee jerk and numbs the front of the thigh and inner leg; patients may find the knee giving way. Surgeons identify it early to protect it. Anaesthetists block it just below the inguinal ligament, alone or as part of a fascia iliaca block, for hip fractures and knee surgery. The femoral nerve stretch test, extending the hip with the patient lying prone, provokes thigh pain when an upper lumbar root is compressed.

Course and supply

Arises from

Ventral rami L2-L4 (posterior divisions), within psoas major; emerges at the muscle's lateral border.

Ends in

Breaks up a few centimetres below the inguinal ligament into muscular, cutaneous and articular branches; its longest branch, the saphenous nerve, reaches the medial foot.

Supplies

Motor to iliacus, pectineus, sartorius and quadriceps femoris (with articularis genus); sensory to the front and medial thigh, the medial leg and foot, and the hip and knee joints.