Femoral nerve lesions

Femoral nerve lesions are characterized predominantly by:

• Paralysis of the quadriceps, leading to failure of leg extension and some weakness of hip flexion
• Variable sensory loss over the antero-medial thigh, anterior knee, medial lower leg, and medial foot to the base of the great toe

Anatomy

Course of the femoral nerve

• Originates from L2, L3, L4 via the lumbar plexus
• Emerges lateral to psoas, passes beneath the inguinal ligament
• Enters femoral triangle lateral to femoral artery
• Divides ~5 cm below ligament into:
  1. Anterior division
  2. Posterior division, which continues as the saphenous nerve
  • Descends through adductor canal
  • Emerges between sartorius and gracilis
  • Runs with saphenous vein, anterior to medial malleolus to the medial foot

Femoral nerve innervations

Anterior division:

• Medial femoral cutaneous nerve (medial thigh)
• Intermediate femoral cutaneous nerve (anterior thigh)
• Nerve to sartorius
• Nerve to pectineus

Posterior division:

• Saphenous nerve (medial leg/foot to great toe base)
• Muscular branch to quadriceps femoris

---

PathologyCauses of femoral nerve lesions

1. Trauma:
   • Direct blunt or penetrating injury
   • Especially within the femoral triangle (superficial course)
   • Associated with femoral shaft fractures
2. Neuropraxia:
   • e.g., due to anterior thigh compartment syndrome
3. Mass lesions:
   • Tumours
   • Abscesses
   • Aneurysms
4. Neuropathies:
   • Rarely affects femoral nerve in mononeuropathies

Clinical Assessment

Typical features include:

• Weak hip flexion
• Loss of knee extension
• Sensory deficits in the described cutaneous distributions

Investigations

When the diagnosis is clear, investigation may not be required.

Consider based on clinical suspicion:

Blood tests:

• FBC
• U&Es / Glucose
• CRP
• ESR
• Heavy metals or others as clinically indicated

Nerve conduction studies:

• Confirm diagnosis
• Rule out generalised neuropathy
• Determine extent and prognosis

CT / MRI:

• Assess for mass lesions or direct nerve visualization

Nerve biopsy:

• Rarely indicated
• Consider in:
  • Mononeuritis
  • Suspected leprosy

Management

1. Treat underlying cause
2. Fasciotomy for compartment syndrome if indicated
3. Occupational therapy:
   • Supportive devices/splints
4. Physiotherapy:
   • Aid recovery or prevent complications

Disposition

Dependent on:

• Cause
• Severity
• Onset timing

---

Appendix 1

Common Peroneal Nerve Anatomy

---

Appendix 2

---

References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Coni R. Neuro 101: Peripheral Nervous System. LITFL
• Nickson C. Myotomes and Differentiating Nerve Lesions. LITFL