Nerves and Vessels of the Lower Limb

Nerves and Vessels of the Lower Limb

Lumbosacral Plexus

The lower limb is innervated by the lumbosacral plexus formed from anterior rami of L1–S4. The lumbar plexus (L1–L4) lies within psoas major; the sacral plexus (L4–S4) lies on the posterior pelvic wall anterior to piriformis.

Key nerves:

• Femoral nerve (L2–L4, posterior divisions): emerges lateral to psoas, passes beneath the inguinal ligament into the femoral triangle. Supplies anterior thigh muscles (iliopsoas, quadriceps, sartorius) and skin of anterior thigh and medial leg (via saphenous nerve). Femoral nerve injury causes inability to extend the knee.
• Obturator nerve (L2–L4, anterior divisions): passes through the obturator foramen into the medial thigh. Supplies medial compartment (adductors, gracilis). Injury causes weakness of adduction.
• Superior gluteal nerve (L4–S1): exits greater sciatic foramen above piriformis. Supplies gluteus medius, minimus, tensor fascia latae.
• Inferior gluteal nerve (L5–S2): exits below piriformis. Supplies gluteus maximus.
• Sciatic nerve (L4–S3): largest nerve in the body; exits below piriformis, descends through posterior thigh deep to gluteus maximus. At the apex of the popliteal fossa it divides into the common fibular nerve (L4–S2) and tibial nerve (L4–S3). The tibial nerve supplies the posterior compartments of the leg and sole; the common fibular wraps around the fibular neck (vulnerable to fracture here) and splits into superficial (lateral compartment) and deep (anterior compartment) fibular nerves.

Topographic Spaces

• Femoral triangle (inguinal ligament / sartorius / adductor longus): contains the femoral nerve, artery, vein (lateral to medial: NAVe), and deep inguinal lymph nodes. The femoral sheath encloses the artery and vein.
• Adductor canal (Hunter's canal): transmits the femoral artery/vein and saphenous nerve from mid-thigh to the adductor hiatus, where the vessels enter the popliteal fossa.
• Popliteal fossa (biceps femoris / semitendinosus and semimembranosus / gastrocnemius heads): contains the popliteal artery (deepest), vein, and tibial + common fibular nerves.

Arterial Supply

The aorta bifurcates at L4 into common iliac arteries → internal iliac (pelvic structures) + external iliac → femoral artery (below inguinal ligament) → profunda femoris (deep femoral, supplies thigh) + continues to popliteal artery → anterior tibial artery (passes through interosseous membrane → dorsalis pedis) + posterior tibial artery (passes behind medial malleolus → medial and lateral plantar arteries). The fibular artery branches from the posterior tibial.

Venous Drainage

The great saphenous vein (GSV) runs from the dorsal venous arch of the foot, anterior to the medial malleolus, up the medial leg and thigh, to drain into the femoral vein at the saphenous opening. The small saphenous vein drains the lateral foot, runs behind the lateral malleolus up the posterior leg, and drains into the popliteal vein. Perforator veins connect the superficial to deep systems; incompetent valves cause varicose veins.