J) Nerves Of The Lower Limb

Lumbar Plexus

The lumbar plexus is the meeting and branching of nerves arising from the ventral roots of L1 to L4. It provides supply to the perineum, lower abdominal wall and the upper thigh. It lies within the posterior part of psoas major.
From superior to inferior, the branches of the lumbar plexus are:

  • The iliohypogastric nerve arises from the upper division of the L1 nerve root. It passes laterally and then anteriorly around the abdominal wall. It supplies the skin of the posterolateral gluteal and suprapubic regions.
  • The ilioinguinal nerve is the other branch of the upper division of the L1 nerve route. It follows a similar route but instead enters the inguinal canal. It supplies the skin of the medial thigh, the root of the penis and upper scrotum (males) or the mons pubis and anterior labia majora (females)
  • The genitofemoral nerve arises from the union of the lower branch of L1 and a separate twig from the ventral branch of L2. It descends beneath the peritoneum an divides into a genital branch (passes through inguinal canal, supplying scrotal skin (men) or mons pubis/labia majora (women)) and femoral branch (accompanies external iliac and supplies skin of medial femoral triangle).
  • The lateral cutaneous nerve of the thigh arises as a small nerve from the dorsal branch of L2. They exit the abdomen beneath the inguinal ligament, about 1 cm medial of the anterior superior iliac spine. It supplies the anterior and lateral skin of the thigh to the knee
  • The femoral nerve arises from the dorsal branches of L2 - L4. It passes inferiorly, initially through the psoas muscle and then between the iliacus and psoas. It exits the abdomen via the retroinguinal space, lateral to the femoral vessels. In the femoral triangle, it divides into anterior and posterior division.
    • The anterior division gives off muscular branch to sartorious as well as the medial and intermediate cutaneous nerves of the thigh, supplying the skin of the medial and anterior thigh to the knee.
    • The posterior division supplies the quadriceps and gives rise to the saphenous nerve. This long nerve accompanies the femoral artery to the adductor canal, before passing inferomedially to the long saphenous vein. It supplies the skin of the medial knee, lower keg and foot to the distal joint of the 1st metatarsal.
  • The obturator nerve is formed by the ventral branches of L2 - L4. It emerges from the psoas at the pelvic brim and descends over obturator internis to the obturator foramen. It then divides into an anterior branch, supplying the adductor muscles except adductor magnus (supplied by the posterior division).
  • The lumbosacral trunk is formed by a dorsal branch of L4 and the dorsal branch of L5. It contributes to the supply of the sciatic and gluteal nerves.

Lumbosacral plexus

The lumbosacral plexus is formed by the ventral nerve roots of L4 to S3 (and sometimes S4). The lumbosacral plexus lies on the piriformis muscle, anterior to the sacrum.

  • The sciatic nerve is the largest peripheral nerve in the body. It is formed by the ventral nerve roots of L4 to S3. It leaves the pelvis through the greater sciatic notch (inferior to piriformis) and descends within the posterior thigh behind adductor magnus. During its descent it supplies the posterior compartment (hamstring muscles) and part of adductor magnus. At about the apex of the popliteal fossa it divides into the common fibular and tibial nerves.
    • The tibial nerve passes inferiorly through the popliteal fossa, initially lateral, then superficial and finally medial to the popliteal vessels. it accompanies the posterior tibial artery, passing posterior to the medial malleolus. It is deep in the proximal lower leg but relatively superficial in the distal lower leg. The tibial nerve supplies branches to the plantar flexors of the heel and flexors of the toes.
    • The sural nerve is a larger branch of the tibial that passes beneath the lateral malleolus, supplying the skin of the posterior lower leg and the lateral side of the foot.
    • The common fibular nerve passes through the lateral popliteal fossa. Winding around the outer surface of the proximal fibula, it divides into deep and superficial fibular nerves. The superficial nerve lies in the lateral compartment of the lower leg, and supplies the compartment and the skin of the dorsum of the foot. The deep nerve accompanies the anterior tibial nerve along the anterior side of the interosseus membrane to enter the dorsum of the foot. It supplies the anterior compartment of muscles.
  • The superior gluteal nerve arises from the dorsal branches of L4 to S1. It leaves the pelvis via the greater sciatic foramen, superior to the piriformis muscle, and supplies gluteus medius and minimus.
  • The inferior gluteal nerve arises from dorsal branches of L5 to S2. It also leaves the pelvis via the greater sciatic foramen, but inferior to the piriformis. It supplies gluteus maximus.
  • The perforating cutaneous nerve arises from the posterior aspect of the ventral division of S2 and S3. It passes through the sacrotuberous ligament, beneath gluteus maximus and supplies the skin of the inferior buttock.
  • The pudendal nerve is the primary nerve of the perineum. It arises from the ventral divisions of S2 to S4, exits through the greater sciatic foramen inferior to piriformis, and then unites with the internal pudendal vessels to enter the perineum through the lesser sciatic notch. It runs in the pudendal canal, between obturator internus and the pelvic wall. It gives off the inferior rectal nerve, perineal nerve and dorsal nerve of the penis/clitoris in this canal.
  • Parasympathetic nerves from S2 to S4 form the inferior splanchnic nerves which carry parasympathetic supply to the prostate, external geniatlia, rectum and bladder.