Sacral plexus
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The sacral plexus is formed by anterior rami of L4 to S5 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 foramen of the sacrum. It forms a triangular shape with an inferiorly pointing apex.
The anterior sacral rami give off six branches and then divide into the anterior and posterior division, each giving off further branches (see below).
Branches
Anterior rami
- nerve to piriformis (S1-S2)
- perforating cutaneous nerve (S2-S3)
- posterior femoral cutaneous nerve (S1-S3)
- parasympathetic pelvic splanchnic nerves (S2-S4)
- pudendal nerve (S2-S4)
- perineal branch (S4)
See: mnemonic.
Anterior division of anterior rami
- nerve to quadratus femoris and inferior gemellus muscles (L4-S1)
- nerve to internal obturator and superior gemellus muscles (L5-S2)
- tibial portion (L4-S3) of the sciatic nerve (L4-S3)
See: mnemonic.
Posterior division of anterior rami
- superior gluteal nerve (L4-S1)
- inferior gluteal nerve (L5-S2)
- common peroneal portion (L4-S2) of the sciatic nerve (L4-S3)
See: mnemonic.
Relations
- anteromedial: common iliac artery and vein; ureter
- anterior: lateral sacral artery and vein
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
-<a href="/articles/pudendal-nerve">pudendal nerve</a> (S2-S4)</li>- +<a href="/articles/pudendal-nerve-1">pudendal nerve</a> (S2-S4)</li>
-<a href="/articles/perineal-branch">perineal branch</a> (S4)</li>- +<a title="Perineal branch of pudendal nerve" href="/articles/perineal-nerve">perineal branch</a> (S4)</li>
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