PNS: Femoral Nerve

Femoral Nerve Anatomy

• The femoral nerve originates from the lumbar plexus, specifically from nerve roots L2-L4.
• It has a deep motor branch and a superficial cutaneous branch, also known as the cutaneous or anterior cutaneous nerve.
• It also gives rise to the saphenous nerve, a large cutaneous nerve following a similar path to the great saphenous vein along the medial lower limb.

Palpation of the Femoral Nerve

• The femoral nerve exits L2-L4 and runs through or along the inferior edge of psoas major in the abdomen and innervates the iliacus there.
• It becomes palpable at the inguinal ligament, emerging underneath at the mid-point, where it enters the femoral triangle.
• The femoral triangle boundaries include the inguinal ligament, the sartorius, and the adductor longus.
• In the femoral triangle, the femoral nerve is the lateral-most structure, followed by the femoral artery and then the femoral vein from lateral to medial.
• Palpating a pulse in the femoral triangle and moving slightly lateral allows placement of your fingers near the femoral nerve.
• About 4cm distal to the inguinal ligament, the femoral nerve splits into an anterior and a posterior branch.
• The anterior branch supplies the pectineus and sartorius and gives off the anterior cutaneous branch for sensory innervation to most of the anterior thigh.
• The posterior branch goes deeper to supply the quads, and gives off the saphenous nerve for sensory innervation to the medial lower leg.
• Palpate the anterior cutaneous branch most directly about a palm width below the ASIS directly over the rec fem, or about 3-fingers' width above the superior pole of the patella directly over the rec fem, the vastus lateralis, and the vastus medialis.
• Palpate the saphenous branch in the space behind the vastus medialis and above the adductor.
• It runs between the muscle layer and superficial fascia down the medial lower extremity until stopping just distal to the extensor retinaculum of the ankle.
• It gives rise to peripatellar nerves which innervate the superficial fascia and skin around the patellar, including the patella retinaculum.
• Palpation of affected tissue assesses tone and tissue health through the quads.

Function of the Femoral Nerve

• Motor functions include the iliacus, pectineus, sartorius, rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
• (Anterior) Cutaneous sensory function includes skin over the quads (excluding the lateral thigh).
• Saphenous sensory function includes skin over the kneecap and medial leg.

Pathophysiology - Femoral Nerve Injuries

• The femoral nerve can be subject to injuries such as Neuropraxia, Axonotmesis, and Neurotmesis.
• Context for determining the correct treatment is very important.
• MOI (Mechanism of Injury) includes:
  • Fractures of hip or pelvis
  • Iatrogenic causes (surgical procedures - hernia)
  • Compression within psoas major & inguinal ligament
  • Compression from tumor or hematoma

Signs & Symptoms of Femoral Nerve Degeneration

• Motor symptoms:
  • Quadriceps wasting; loss of patellar reflex
  • Loss of knee extension and some hip flexion
  • Inability to control knee motion during walking gait
• Sensory symptoms:
  • Loss of sensation over the front and medial side of the thigh, medial aspect of the lower leg and foot
  • Possible mild pain at the inguinal ligament (midpoint)

Femoral Nerve Assessment

• Prone Knee Bending Test assesses the Femoral nerve.
• Prone Knee Extension Test assesses the Saphenous nerve.
• Femoral Nerve Traction Test assesses the Femoral nerve.
• Varying degrees of weakness depending on degree of severity can be observed in MMT Quads, RROM Knee Ext, and RROM Hip Flexion.
• Patellar tendon reflex will be diminished.
• Sensory testing demonstrates decreased sensation in cutaneous distributions.