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Structure

Lumbosacral plexus

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The lumbosacral plexus is formed by the ventral rami of L1-S4 and supplies the lower limb, pelvis and perineum. It is described as the lumbar plexus (L1-L4) and the sacral plexus (L4-S4), which are linked by the lumbosacral trunk.

Terminologia Anatomica (Latin): Plexus lumbosacralis · Open in the 3D atlas

Location

The lumbar plexus lies within or behind the psoas major muscle, in front of the lumbar transverse processes; the sacral plexus lies on the posterior pelvic wall in front of piriformis, behind the internal iliac vessels.

Structure

Lumbar plexus: iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral (L2-L4, posterior divisions) and obturator (L2-L4, anterior divisions). Sacral plexus: superior and inferior gluteal, sciatic (L4-S3, tibial and common fibular parts), posterior femoral cutaneous, pudendal (S2-S4) and nerves to piriformis, obturator internus and quadratus femoris.

Blood supply

Lumbar plexus: lumbar arteries and the iliolumbar artery. Sacral plexus: branches of the internal iliac artery (superior and inferior gluteal, internal pudendal, lateral sacral); the sciatic nerve also has its own companion artery from the inferior gluteal artery.

Innervation

Femoral nerve: hip flexion and knee extension (anterior thigh, quadriceps), skin of the anterior thigh and medial leg (saphenous). Obturator nerve: thigh adductors, medial thigh skin. Sciatic nerve: hamstrings, then via tibial (posterior leg and sole) and common fibular (anterior and lateral leg, foot dorsiflexion and eversion) nerves. Gluteal nerves: gluteus medius, minimus, maximus. Pudendal nerve: perineum.

Function

It provides motor and sensory supply to the anterior, medial and posterior thigh, the leg and foot, the gluteal region, and the pelvic floor and perineum including voluntary anal and urethral sphincters, with autonomic fibres to the pelvic organs (S2-S4 pelvic splanchnic nerves).

Clinical correlations

Femoral neuropathy weakens knee extension; obturator injury impairs adduction. Sciatic injury may follow hip dislocation, posterior acetabular fracture or poorly placed gluteal injection (upper outer quadrant is the safer site). Common fibular nerve injury at the fibular neck gives foot drop. Superior gluteal nerve injury produces a Trendelenburg gait. Lumbar disc herniation causes radiculopathy (for example L5 or S1 sciatica); cauda equina syndrome is an emergency.

Common exam points

  • Lumbar plexus L1-L4 (femoral and obturator: L2-L4); sacral plexus L4-S4 (sciatic L4-S3, pudendal S2-S4).
  • Femoral nerve: quadriceps (knee extension), saphenous nerve to medial leg.
  • Sciatic nerve divides into tibial and common fibular nerves; common fibular injury gives foot drop.
  • Superior gluteal nerve injury: Trendelenburg sign.
  • Gluteal injection in the upper outer quadrant to protect the sciatic nerve.
  • Pudendal nerve (S2-S4) supplies the perineum; it can be blocked near the ischial spine.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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