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This article is closely associated with the article on the Lumbar Plexus, as both the lumbar and sacral plexuses supply peripheral nerves to the lower limb (this nerve supply is called innervation).
The sacral plexus is a convergence of spinal nerves that lies on the posterior pelvic wall, in front of the piriformis muscle (a muscle in the buttock). It includes input from six spinal nerves (L4 [lumbar nerve 4], L5, S1 [sacral nerve 1], S2, S3 and S4) and gives rise to several branches. The five major nerves discussed here are superior gluteal, inferior gluteal, sciatic, posterior femoral cutaneous and pudendal.
Each of these peripheral nerves will be discussed individually throughout the article.
The mnemonic “Sassy Irish Sailors Pester Parrots” recalls the order of the five nerves in this teaching list: superior gluteal, inferior gluteal, sciatic, posterior femoral cutaneous and pudendal. These list positions do not describe an invariant anatomical sequence of branch origins, and smaller branches are not included in the mnemonic.
The five major nerves discussed here leave the pelvis through the greater sciatic foramen (a large opening at the back of the pelvis). This is not the route of every sacral plexus branch: the nerve to levator ani (the main muscle of the pelvic floor) goes straight to that muscle within the pelvis.
Schematic - Root contributions to selected branches of the sacral plexus. Superior gluteal: L4, L5 and S1. Inferior gluteal: L5, S1 and S2. Tibial portion: L4, L5, S1, S2 and S3. Common fibular portion: L4, L5, S1 and S2. Posterior femoral cutaneous: S1, S2 and S3. Pudendal: S2, S3 and S4. The tibial and common fibular portions form the sciatic nerve (L4–S3). This schematic shows root contributions, not spatial anatomy or the order in which branches arise.
SimpleMed root-contribution schematic, 2026. Previous diagram by Dr. Maddie Swannack.
Peripheral Nerves of the Sacral Plexus
The superior gluteal nerve is a major branch of the sacral plexus.
It leaves the pelvis through the greater sciatic foramen, superior to the piriformis muscle.
It has three spinal nerve contributions: L4, L5 and S1.
The motor functions of the superior gluteal nerve include the gluteus minimus, gluteus medius and the tensor fascia lata (a muscle on the outer side of the hip).
It has no sensory functions.
The inferior gluteal nerve is listed second in the five-name mnemonic used here.
It leaves the pelvis through the greater sciatic foramen, inferior to the piriformis muscle.
It has three spinal nerve contributions: L5, S1 and S2.
The motor function of the inferior gluteal nerve is the innervation of gluteus maximus.
It has no sensory functions.
The sciatic nerve is the largest nerve in the body, approximately 2 cm wide, and is listed third in the five-name mnemonic used here. It can be considered to be two separate nerves within the same fibrous sheath: the tibial nerve and the common peroneal nerve (also known as the common fibular nerve). In most people, the sciatic nerve separates into the two constituents just superiorly to the popliteal fossa (the hollow behind the knee), but they may separate at any point superior to this.
It leaves the pelvis through the greater sciatic foramen, emerging inferiorly to the piriformis muscle (in most people). It passes over the muscles of the deep gluteal region and enters the posterior thigh by passing deep to the long head of biceps femoris. Within the posterior thigh, it gives off the branches to the hamstring muscles and to the adductor magnus. Only the hamstring part of adductor magnus is supplied by the sciatic nerve: the rest is supplied by the obturator nerve. When the sciatic nerve reaches the superior border of the popliteal fossa, it divides into the tibial and common peroneal nerves.
Spinal Nerve Contributions
- Sciatic - to the sciatic nerve as a whole, the following nerves contribute: L4, L5, S1, S2, and S3.
- Tibial - the tibial portion receives L4, L5, S1, S2 and S3 (every root that contributes to the sciatic nerve).
- Common Peroneal (Common Fibular) - the common fibular portion receives L4, L5, S1 and S2 (L4–S2). The sciatic nerve as a whole remains L4–S3.
- The sciatic, tibial and common peroneal nerves all have individual motor functions. The muscles are described by compartment (a group of muscles that share a nerve supply and a layer of connective tissue):
- Sciatic - posterior compartment of the thigh (biceps femoris, semitendinosus, semimembranosus; the short head of biceps femoris is the exception, as it is supplied by the common peroneal part) and the hamstring portion of adductor magnus.
- Tibial - posterior compartment of the leg (gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor digitorum longus and flexor hallucis longus) and most of the intrinsic muscles of the foot (the small muscles that lie wholly within the foot), including all of those in the sole.
- Common Peroneal - the short head of biceps femoris, the anterior compartment of the leg (tibialis anterior, extensor digitorum longus, extensor hallucis longus) and the lateral compartment of the leg (fibularis longus and fibularis brevis). In the foot it supplies only two small muscles on the top of the foot (extensor digitorum brevis and extensor hallucis brevis).
- In summary, the sciatic nerve and its branches supply the muscles of the posterior thigh and all the muscles of the leg and foot.
- The sciatic nerve itself does not provide any sensory innervation, but the tibial and common peroneal branches do.
- Tibial - sole of the foot.
- Common Fibular - its branches supply the anterolateral lower leg and the dorsum (top) of the foot, including the first interdigital cleft (the skin between the big toe and the second toe) via the deep fibular nerve.
The posterior femoral cutaneous nerve (cutaneous means of the skin) is listed fourth in the five-name mnemonic used here.
It has three spinal nerve contributions: S1, S2, and S3.
It leaves the pelvis via the greater sciatic foramen, inferior to the piriformis. It then travels inferiorly, deep to gluteus maximus, and down the posterior thigh to the knee.
The posterior femoral nerve has no motor functions.
Its sensory innervation includes the posterior surface of the thigh and part of the back of the leg, as well as the perineum (the area between the genitals and the anus).
The pudendal nerve is listed fifth and last in this five-name mnemonic; it is not the final anatomical branch of the entire plexus.
It leaves the pelvis via the greater sciatic foramen, then enters the perineum via the lesser sciatic foramen. It then runs forward along the side wall of the ischioanal fossa (also called the ischiorectal fossa), a fat-filled space beside the anus, between the anal canal and the ischium (the lower part of the hip bone). Here it lies in a tunnel of connective tissue called the pudendal canal (Alcock’s canal).
It has contributions from three spinal nerves: S2, S3, and S4.
The motor functions of the pudendal nerve include the skeletal muscles of the perineum, the external urethral sphincter and the external anal sphincter. This gives rise to the saying ‘S2, S3 and S4 keep sh*t off the floor’ referencing the roots of the pudendal nerve.
The sensory functions of the pudendal nerve include the penis, the clitoris and the skin of the perineum.
Other Branches of the Sacral Plexus
Along with the five major peripheral nerves produced by the sacral plexus, there are a number of smaller branches that are not shown on the diagram. They are generally nerves that are directly supplying muscles:
- Nerve to piriformis
- Nerve to obturator internus (also supplies the gemellus superior, a small muscle of the buttock)
- Nerve to quadratus femoris (also supplies the gemellus inferior, a small muscle of the buttock)
The Pelvic Splanchnic Nerves (splanchnic means to do with the internal organs) are separate from these muscular branches and provide parasympathetic innervation to the hindgut (the last part of the large bowel) and to the pelvic organs.
Pathologies of the Sacral Plexus
Damage to the Lumbosacral Plexuses
Damage to the lumbar or sacral plexuses (or both) can cause substantial disability and is suspected when the symptoms cannot be localised to a single peripheral nerve region.
Plexus damage can present with neuropathic pain (pain caused by nerve damage), numbness, weakness or wasting of muscles.
One of the main causes is diabetic amyotrophy (muscle wasting caused by nerve damage in diabetes), also known as lumbosacral radiculoplexus neuropathy (a disease of the nerve roots and the plexus). It is thought to occur due to an immune mediated inflammatory process affecting the nerves, often in people with diabetes. Immunosuppressive treatments (medicines that dampen the immune system), such as corticosteroids, have been used in some cases, but evidence for their benefit is limited.
Another cause is a nearby tumour growing into or pressing on the plexus. Nerve damage can also happen during or after surgery, or after radiotherapy (treatment with radiation). Management depends on the underlying cause and may include surgery, radiotherapy or other cancer treatments such as chemotherapy, with a risk of further nerve damage.
Piriformis Syndrome
Piriformis syndrome is a clinical syndrome caused by compression of the sciatic nerve by the piriformis muscle, resulting in pain, numbness and muscle weakness. The diagnosis is made from the history and examination, and other conditions can mimic it (lumbar canal stenosis, which is narrowing of the spinal canal in the lower back, disc problems or pelvic causes). Treatment options can range from analgesia (pain relief) and physiotherapy, to corticosteroid injections, to surgery to release the pressure on the nerve.
Edited by: Dr. Ben Appleby
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
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