CorpusHuman Anatomy
NervousPlexus

Sacral plexus

Plexus sacralis

Also known as: lumbosacral plexus, L4–S4 plexus, inferior gluteal nerve, posterior femoral cutaneous nerve

A plexus on the posterior pelvic wall formed by the lumbosacral trunk (L4–L5) and the ventral rami of S1–S4. It supplies the gluteal region, the posterior thigh, the whole leg and foot below the knee (except the saphenous territory), and the perineum.

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Overview

RootsL4–S4
Lies onPiriformis
Largest branchSciatic nerve (L4–S3)
Exit routeGreater sciatic foramen (above/below piriformis)

The sacral plexus lies on the anterior surface of piriformis, deep to the parietal pelvic fascia and behind the internal iliac vessels and ureter. It is formed by the lumbosacral trunk (L4 and L5, descending over the ala of the sacrum) and the ventral rami of S1–S4, which emerge from the anterior sacral foramina. The roots converge toward the greater sciatic foramen, through which most branches leave the pelvis. Branches that pass above piriformis are the superior gluteal nerve and vessels. Branches that pass below piriformis are the sciatic, inferior gluteal, posterior femoral cutaneous and pudendal nerves, the nerves to obturator internus and quadratus femoris, and the inferior gluteal and internal pudendal vessels.

Like the other plexuses, it has anterior (ventral) and posterior (dorsal) divisions. The tibial nerve comes from anterior divisions (flexors). The common fibular nerve and the gluteal nerves come from posterior divisions (extensors and abductors). The pelvic splanchnic nerves (S2–S4, parasympathetic) arise from the plexus roots.

Location

Posterior pelvic wall, on piriformis, converging toward the greater sciatic foramen.

Anatomy

Innervation

- Muscles: the gluteal muscles, the short lateral rotators of the hip, the hamstrings, all the muscles of the leg and foot, and the pelvic floor and perineal muscles.
• Skin: the buttock, the posterior thigh, the leg (except medially) and foot, and the perineum.

Nerve roots

L4, L5 (lumbosacral trunk), S1, S2, S3, S4.

Branches

- Superior gluteal (L4–S1): above piriformis; gluteus medius, gluteus minimus and tensor fasciae latae.
• Inferior gluteal (L5–S2): below piriformis; gluteus maximus.
• Sciatic (L4–S3).
• Posterior femoral cutaneous (S1–S3): skin of the posterior thigh, popliteal fossa, lower buttock and perineum.
• Pudendal (S2–S4).
• Nerve to obturator internus (L5–S2): also superior gemellus.
• Nerve to quadratus femoris (L4–S1): also inferior gemellus.
• Nerve to piriformis (S1–S2).
• Perforating cutaneous nerve (S2–S3).
• Nerves to levator ani and coccygeus (S3–S4).
• Pelvic splanchnic nerves (S2–S4).

Function

  • Hip extension (gluteus maximus), abduction and pelvic stabilisation (gluteus medius and minimus), and lateral rotation (short rotators)
  • Knee flexion (hamstrings) and all movements of the ankle and foot (via the sciatic nerve)
  • Sensation of the buttock, posterior thigh, most of the leg and foot, and the perineum
  • Support of the pelvic floor, continence and sexual function (pudendal and pelvic splanchnic nerves)

Clinical significance

Sacral plexopathy

Pelvic tumours (rectal, cervical and prostate cancer, lymphoma), radiation, pelvic fractures and haematomas can damage the plexus. The result is a painful, multi-nerve deficit: buttock and leg pain, weakness of hip extension and abduction plus a sciatic-pattern weakness, and often bladder and bowel involvement. Compression by the fetal head during labour causes transient cramp-like pain down the back of the leg.

Mnemonics

S2, 3, 4

"S2, 3, 4 keeps the pelvic floor up off the floor." These segments supply levator ani and the external sphincters (pudendal) and the parasympathetic pelvic splanchnics for bladder, bowel and erection.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.