Sacral plexus

Last revised by Craig Hacking on 11 Oct 2022

The sacral plexus is formed by anterior rami of L4 to S4 and its branches innervate the pelvis, perineum and lower limb.

Gross anatomy

The sacral plexus forms on the anterior belly of the piriformis muscle and is formed by the lumbosacral trunk (L4-5) of the lumbar plexus, which enters the pelvis coursing medially to psoas major and unites with the ventral rami of the S1 to S4 nerve roots, which emerge from the anterior foramina of the sacrum. It forms a triangular shape with an inferiorly pointing apex. 

The are a total of twelve branches5. The anterior sacral rami give off six branches and then divide into the anterior and posterior divisions, which provide a further three branches each (see below). 

Anterior rami

See: mnemonic.

Anterior division of anterior rami

See: mnemonic.

Posterior division of anterior rami

See: mnemonic.

  • medial 
    • anterior sacral foramina
    • sympathetic trunk
  • posterior
    • piriformis
  • anterior
    • parietal pelvic fascia
    • lateral sacral arteries and veins
    • common iliac vessels on top of lumbrosacral trunk
    • internal iliac vessels
    • ureter (in front of internal iliac vessels) lies well anterior to upper part of plexus 

Variant anatomy

  • common peroneal and tibial parts of the sciatic nerve fail to unite and course into the lower limb separately
  • additional caudal nerve root contribution to the sacral plexus 6

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Cases and figures

  • Figure 1: sacral plexus diagrams
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  • Figure 2: posterior sacral nerves (Gray's illustration)
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  • Figure 3: sacral plexus (Gray's illustrations)
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  • Figure 4: sacral plexus (Gray's illustrations)
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