Boundaries and contents
Two foramina connect the gluteal region to the pelvis and perineum. The sacrotuberous and sacrospinous ligaments convert the greater and lesser sciatic notches of the hip bone into the greater and lesser sciatic foramina. Piriformis fills most of the greater foramen, dividing it into a space above and a space below.
| Route | Structures |
|---|---|
| Greater sciatic foramen, above piriformis | Superior gluteal nerve, artery and vein |
| Greater sciatic foramen, below piriformis | Sciatic nerve; inferior gluteal nerve, artery and vein; posterior cutaneous nerve of the thigh; nerve to quadratus femoris; pudendal nerve; internal pudendal vessels; nerve to obturator internus |
| Lesser sciatic foramen | Tendon of obturator internus (out); pudendal nerve, internal pudendal vessels and nerve to obturator internus (in, to the perineum) |
Below piriformis lie the short lateral rotators, from above down: superior gemellus, obturator internus, inferior gemellus and quadratus femoris. Obturator internus arises inside the pelvis, turns through a right angle around the lesser sciatic notch and, with the two gemelli on either side (together called triceps coxae), inserts on the medial surface of the greater trochanter. Obturator externus lies deep to quadratus femoris. All these muscles lie directly on the back of the hip joint capsule.
Nerves of the gluteal region
All the deep nerves of the buttock come from the sacral plexus.
- Sciatic nerve (L4–S3): emerges below piriformis, runs down over the gemelli, obturator internus and quadratus femoris, midway between the ischial tuberosity and the greater trochanter, and enters the thigh under gluteus maximus. It supplies no gluteal muscle.
- Superior gluteal nerve (L4–S1): runs forwards between gluteus medius and minimus to supply both and tensor fasciae latae.
- Inferior gluteal nerve (L5–S2): enters the deep surface of gluteus maximus, its only muscle.
- Posterior cutaneous nerve of the thigh (S1–S3): runs down superficial to the sciatic nerve, gives the inferior cluneal nerves around the lower border of gluteus maximus, and supplies the back of the thigh.
- Nerve to obturator internus (superior gemellus too) and nerve to quadratus femoris (inferior gemellus and the hip joint too).
- Pudendal nerve (S2–S4): crosses the ischial spine and re-enters through the lesser sciatic foramen to the perineum. Its inferior rectal branch crosses the ischioanal fossa to the external anal sphincter and perianal skin.
The skin of the buttock is supplied by the superior cluneal nerves, from the dorsal rami of L1–L3 crossing the iliac crest; the middle cluneal nerves from S1–S3 dorsal rami; and the inferior cluneal nerves.
Blood supply and anastomoses
The gluteal region is supplied by the superior and inferior gluteal arteries, both branches of the internal iliac. The superior gluteal artery, the largest branch, comes from the posterior division and emerges above piriformis; its superficial branch supplies gluteus maximus and its deep branch runs between medius and minimus. The inferior gluteal artery, from the anterior division, emerges below piriformis and supplies maximus and the upper hamstrings.
Two anastomoses link these arteries with the femoral system. The trochanteric anastomosis, near the trochanteric fossa, joins the gluteal arteries with both circumflex femoral arteries and sends branches to the femoral head. The cruciate anastomosis, at the level of the lesser trochanter, joins the inferior gluteal, both circumflex femoral and the first perforating arteries, and can bypass a blocked femoral or external iliac artery.
Clinical relevance
The sciatic nerve is the main structure at risk in the buttock.
- Posterior hip dislocation: the femoral head is driven back onto the sciatic nerve, usually in a dashboard injury. The common fibular part is more often damaged, causing foot drop.
- Intramuscular injection: the sciatic nerve runs through the lower inner part of the buttock, so injections go in the upper outer quadrant.
- Posterior approach to the hip: the short rotators are detached from the trochanter and folded back over the sciatic nerve to protect it. Quadratus femoris is often preserved because the medial circumflex femoral artery runs along its upper border.
- Pelvic fractures: the superior gluteal artery can tear at the greater sciatic notch and bleed heavily.
- Superior gluteal nerve injury: causes a Trendelenburg gait.
- Surface marking of the sciatic nerve: a curved line from midway between the posterior superior iliac spine and the ischial tuberosity, through the midpoint between the tuberosity and the greater trochanter, then straight down the back of the thigh.
On the specimen
The station shows the deep gluteal region with gluteus maximus reflected and the neurovascular bundles cleaned. Fix the bony points first: the greater trochanter laterally and the ischial tuberosity medially and below. The large flat nerve running down between them is the sciatic nerve; the thinner nerve lying on it is the posterior cutaneous nerve of the thigh.
The vessels and nerve emerging above piriformis are superior gluteal; those below it, turning into the deep surface of gluteus maximus, are inferior gluteal. The tendon with a small muscle belly above and below it is obturator internus with the gemelli. Deep to the short rotators lies the hip joint capsule. The fine nerve crossing the fat medial to the ischial tuberosity towards the anus is the inferior rectal nerve, and the nerves crossing the iliac crest are the superior cluneal branches of the lumbar dorsal rami.