The Femoral Nerve
The femoral nerve is one of the major peripheral nerves of the lower limb.
In this article, we shall look at the anatomy of the femoral nerve – its anatomical course, motor and sensory functions, and any clinical relevance.
Nerve Roots: L2-L4
Motor: Innervates the anterior thigh muscles that flex the hip joint (pectineus, iliacus, sartorius) and extend the knee (quadriceps femoris: rectus femoris, vastus lateralis, vastus medialis and vastus intermedius),
Sensory: Supplies cutaneous branches to the anteromedial thigh (anterior cutaneous branches of the femoral nerve) and the medial side of the leg and foot (saphenous nerve).
The femoral nerve is the largest branch of the lumbar plexus. It is derived from the nerve roots L2 – L4.
The nerve descends from the lumbar plexus in the abdomen, travelling down through the fibres of psoas major. The nerve exits psoas major at the lower part of its lateral border, passing behind the iliac fascia to approximately the mid-point of the inguinal ligament. It then traverses behind the inguinal ligament into the thigh and splits into an anterior and posterior division.
It passes through the femoral triangle lateral to the femoral vessels (enclosed within the femoral sheath) and gives off articular branches to the hip and knee joints.
The terminal cutaneous branch of the femoral nerve is the saphenous nerve which continues, with the femoral artery and vein, through the adductor canal.
Clinical Relevance: Arterial or Venous Sampling from the Femoral Vessels
If arterial or venous sampling is required from the femoral artery or vein respectively, it is essential to be aware of the order in which the structures lie.
Remembering ‘NAVY’ gives a reminder of the structures from LATERAL to MEDIAL
Lateral – Femoral NERVE – Femoral ARTERY – Femoral VEIN – Medial
The femoral nerve supplies some of the muscles of the anterior thigh
- Pectineus – adducts and flexes the thigh, assists with medial rotation of the thigh.
- Iliacus – acts with psoas major and psoas minor (forming iliopsoas) to flex the thigh at the hip joint and stabilise the hip joint.
- Sartorius – flexes, abducts and laterally rotates the thigh at the hip joint. Flexes the leg at the knee joint.
- Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis and vastus intermedius) – extends the leg at the knee joint. Rectus femoris also steadies the hip joint and assists iliopsoas in flexing the thigh.
The first cutaneous branches of the femoral nerve are the anterior cutaneous branches that arise in the femoral triangle. They supply the skin on the anteromedial thigh.
The last cutaneous branch of the femoral nerve is the saphenous nerve which supplies the skin on the medial side of the leg and the foot.
Stripping of the Saphenous Vein
The saphenous vein is often stripped in individuals with problematic varicose veins. The long saphenous vein is accompanied in its course by the saphenous nerve. Damage to the saphenous nerve during this procedure can lead to pain, paraesthesia or complete loss of sensation the medial side of the lower leg (please see Fig. 2 above for distribution)
Femoral Nerve Block
Femoral nerve block (in combination with a sciatic nerve block) may be indicated in patients requiring lower limb surgery who cannot tolerate a general anaesthetic. A femoral nerve block can also be used as peri- and post-operative analgesia for patients with a fractured neck of femur who cannot tolerate particular analgesics.