Hip flexion and knee extension are crucial to normal gait. The femoral nerve is a branch of the lumbar plexus and enables us to perform these movements. It supplies motor innervation to the iliopsoas muscle, and anterior compartment of the thigh. It supplies sensation over the anterior and medial thigh and medial surface of the leg. 

The femoral nerve arises from the Lumbar Plexus (Ventral rami of L1-L4, the nerve plexus of the lower limb). It arises from posterior divisions of the ventral rami of the L2-L4 nerve roots, with the obturator nerve emerging from the anterior divisions of the L2-L4 nerve roots. You may be wondering why the muscles of the leg have innervation from the lumbar spinal nerves. Would it not make more sense for them to be innervated by the sacral nerves as these muscles do not lie in the lumbar region? This can be explained by the embryological migration of the lumbar musculature down to the thighs i.e. the quadriceps was originally a lumbar muscle.

 

The nerve runs through the psoas major, and emerges lateral to the psoas major. It does not supply the psoas major muscle which gets drect supply from the lumbar plexus. It does supply the iliacus muscle. The nerve then runs toward the anterior superior iliac spine, and runs beneath the inguinal ligament before descending in the groin region laterally to the femoral artery and vein. It then divides into a superficial and deep component. 

The superficial division supplies sartorius and pectineus and forms the intermediate cutaneous nerve of the thigh, and medial cutaneous nerve of the thigh. 

The deep division supplies the anterior compartment of the thigh i.e. quadriceps femoris (vastus medialis, vastus lateralis, vastus intermedius and rectus femoris) and also gives rise to the saphenous nerve. The saphenous nerve runs posterior to the Sartorius muscle in the sub-sartorial (Hunter's) canal, and passes between the sartorius and gracilis muscles. It follows the course of the great saphenous nerve in the medial aspect of the leg and supplies the anteromedial aspects of the knee, leg and foot. The deep division also gives off the infrapatellar branches to the knee, which pierce the fascia lata and sartorius to supply sensation to the skin lying over the patella.

 

As the femoral nerve supplies the anterior compartment of the thigh, you may expect it to arise from the anterior divisions of the ventral rami. It in fact arises from the posterior divisions. The reason for this can be found in the embryology of the musculature. The upper limbs remain in their original position, with the flexor compartments on the anterior surface and the extensor compartments on the posterior surface. Contrastingly, the lower limb rotate a full 180 degrees, which caused the flexor compartment to move to the back, and the extensor compartment to move to the front. The nerve supply to the muscles does not alter, and the artefact of the original positions of the muscles can be seen in the divisions of the nerve roots. 

Developmental precursor- Alar and basal plate of L2-L4

Origin- posterior divisions of anterior rami of L2-L4

Branches- medial cutaneous nerve of the thigh, intermediate cutaneous nerve of the thigh, motor branch

Muscles supplied- Quadriceps femoris, pectineus, Sartorius, iliacus.

Dermatome- medial and intermediate surface of the thigh.

NAVY- this teaches the order of structures in the femoral neurovasculature from lateral to medial (nerve artery vein Y-front)

The femoral nerve is a branch of the lumbar plexus (the nerve plexus of the lower lib). It supplies motor innervation to the anterior compartment of the thigh. It supplies sensation over the anterior and medial thigh and medial surface of the leg. 

Authors:  S Shahid & A Davies