Clinical Relevance: Piriformis Syndrome Piriformis syndrome refers to compression of the sciatic nerve by the piriformis muscle. After its formation, it leaves the pelvis and enters the gluteal region via greater sciatic foramen. An undivided sciatic nerve exits from behind the top part of the piriformis.
It is also known as deep gluteal syndrome. The patient will often experience paresthesias in a dermatomal distribution, either L5 or S1 depending on where the sciatic nerve is being irritated. The tibial nerve continues down the back of the leg to the heel and sole of the foot.
Embryology At the beginning of the third week after fertilization, a process called neurulation begins. The neural plate leads to the neural tube and neural crest cells.
Origin The sciatic nerve is formed by the combination of 5 nerves in the lumbar lower and sacral spine —L4, L5, S1, S2, and S3.
It is a mixed-function nerve, meaning that it contains both sensory neurons and motor neurons.
Fig 1 — Derivation of the sciatic nerve from the sacral plexus.