What is the afferent innervation of the medial, lateral, and posterior leg?

Afferent Innervation of the Medial, Lateral, and Posterior Leg

The afferent innervation of the leg is primarily provided by branches of the femoral, sciatic, and saphenous nerves, with the saphenous nerve supplying the medial aspect, the superficial peroneal nerve supplying the lateral aspect, and the posterior femoral cutaneous and tibial nerves supplying the posterior aspect of the leg.

Medial Leg Innervation

Saphenous Nerve

• Primary sensory nerve for the medial aspect of the leg
• Branch of the femoral nerve (derived from L2-L4)
• Course:
  • Descends through the femoral triangle
  • Travels through the adductor canal (Hunter's canal)
  • Emerges between the sartorius and gracilis muscles
  • Continues distally along the medial aspect of the leg
• Provides sensory innervation to:
  • Medial aspect of the leg from knee to ankle
  • Medial malleolus periosteum and joint capsule 1
  • Extends to the medial side of the foot and base of the great toe

Infrapatellar Branch of Saphenous Nerve (IPBSN)

• Important branch of the saphenous nerve
• Supplies sensation to the anterior and medial knee region
• Emerges through or around the sartorius muscle in 62.6% of individuals 2
• Shows significant anatomical variation:
  • 32.7% of knees have redundant innervation
  • 25.2% have contribution from the intermediate femoral cutaneous nerve 2

Medial Femoral Cutaneous Nerve (MFCN)

• Branch of the femoral nerve
• Supplies the skin on the anterior medial aspect of the thigh and knee 3
• Conduction velocity averages 60 ± 5 m/s 3

Lateral Leg Innervation

Superficial Peroneal Nerve

• Primary sensory nerve for the lateral aspect of the leg
• Branch of the common peroneal nerve (derived from L4-S2)
• Course:
  • Originates from the common peroneal nerve at the neck of the fibula
  • Descends in the lateral compartment of the leg
  • Becomes superficial in the distal third of the leg
• Provides sensory innervation to:
  • Anterolateral aspect of the leg
  • Dorsum of the foot (except the first web space)
  • Medial dorsal cutaneous branch may contribute to medial foot sensation 4

Sural Nerve

• Formed by the union of the medial sural cutaneous nerve (from tibial nerve) and the communicating branch of the common peroneal nerve
• Provides sensory innervation to:
  • Posterolateral aspect of the leg
  • Lateral malleolus
  • Lateral aspect of the foot and fifth toe

Posterior Leg Innervation

Posterior Femoral Cutaneous Nerve (PFCN)

• Originates from the sacral plexus (S1-S3)
• Has a much more distal termination than traditionally described:
  • Terminates in the proximal lower leg in 45.7% of cases
  • Terminates in the distal lower leg in 44.6% of cases
  • Ends at the popliteal region in only 9.7% of cases 5
• Often runs in close proximity to the small saphenous vein (90.3% of cases) 5
• May contribute to periosteal innervation of the fibula or calcaneus 5

Tibial Nerve

• Branch of the sciatic nerve (L4-S3)
• Provides sensory innervation to:
  • Posterior aspect of the leg
  • Plantar aspect of the foot
• Gives rise to the medial calcaneal branches that supply the heel

Clinical Implications

Regional Anesthesia Considerations

• Transsartorial approach to saphenous nerve block is most effective for providing sensory anesthesia to both the medial leg and foot 4
• Complete anesthesia of the lower leg and foot requires blocking the posterior femoral cutaneous nerve in addition to sciatic and femoral/saphenous nerves 5
• Supplemental block of the medial dorsal cutaneous branch of the superficial peroneal nerve may be necessary for complete medial foot anesthesia 4

Surgical Considerations

• No safe zone exists for avoiding the infrapatellar branch of the saphenous nerve during knee procedures 2
• Significant innervation redundancy exists in the infrapatellar region, with substantial contribution from the intermediate femoral cutaneous nerve 2
• The saphenous nerve innervates not only skin but also the periosteum of the medial malleolus and joint capsule, which has implications for ankle pain management 1

Neuropathy Prevention

• Avoid prolonged pressure on the peroneal nerve at the fibular head to prevent peroneal neuropathy 6
• Use specific padding to prevent contact of the peroneal nerve with hard surfaces 6
• Consider the anatomical course of nerves when positioning patients for surgery to prevent stretch injuries 6

Understanding the complex and variable afferent innervation of the leg is essential for effective pain management, regional anesthesia, and prevention of iatrogenic nerve injuries during surgical procedures.