Sacral Plexus

Sacral plexus is a plexus of nerves that lies on the posterior pelvic wall in front of the piriformis muscle. It provides motor and sensory supply to the posterior part of thigh, most of the lower leg and the entire foot. Part of pelvis is also supplied by branches of this plexus.

Structure:

The sacral plexus is formed by:

  • The lumbosacral trunk (formed by anterior rami of fourth and fifth lumbar nerves)
  • Anterior rami of 1st, 2nd, 3rd, and 4th sacral nerves

All the nerves forming the sacral plexus converge towards the lower part of the greater sciatic foramen and unite to form a flattened band. The branches of the sacral plexus arise from anterior and posterior surfaces of this flattened band.

Important relations:

Anterior:

  • Internal iliac vessels and their branches
  • Rectum

Posterior:

  • Piriformis muscle

Branches:

The branches of the sacral plexus can be divided into two categories: branches that supply the lower limb and branches that supply the pelvis.

Branches to the lower limb:

These branches leave the pelvis through the greater sciatic foramen and follow their course into the lower limb. These include:

  • Sciatic nerve:
    It is the largest branch of the plexus and largest nerve in the body. It supplies nearly the whole of the skin of leg, the muscles of back of thigh and the muscles of leg and foot.
  • Superior gluteal nerve:
    It supplies the gluteus medius, gluteus minimus and tensor fascia lata.
  • Inferior gluteal nerve:
    It supplies the gluteus maximus muscle.
  • Nerve to quadratus femoris:
    It supplies the quadratus femoris and inferior gemellus muscles.
  • Nerve to obturator internus:
    It supplies the obturator internus and superior gemellus muscles.
  • Posterior cutaneous nerve of thigh:
    It supplies the skin of buttock and back of the thigh.

Branches to the pelvis:

These branches supply the pelvic viscera, pelvic muscles and perineum. These include:

  • Pudendal nerve:
    It leaves the pelvis through the greater sciatic foramen but then reenters the perineum through the lesser sciatic foramen. It innervates the external genital and voluntary sphincters of bladder and rectum.
  • Nerve to piriformis muscle:
    It supplies the piriformis muscle.
  • Pelvic splanchnic nerves:
    These constitute the sacral part of the parasympathetic nervous system and are distributed to the pelvic viscera.
  • Perforating cutaneous nerve:
    It supplies the skin of the lower medial part of the buttocks.