The Gluteal Region: The Muscles That Made Us Upright
Of all the things that separate a human from every other animal, the most honest one is not the brain — it is the backside. No other creature carries a gluteus maximus like ours. It is the single largest muscle in the body, and it exists because we chose, somewhere deep in our history, to stand up, to climb, and to run. Yet the most important muscles in this region are not the ones you can see. Two flat fans hidden underneath, gluteus medius and minimus, do something so quiet that most people live their whole lives without knowing it happens: every single time you take a step, they stop your pelvis from collapsing towards the leg that is in the air. Walk across a room and you have used them a hundred times. Lose the small nerve that runs them, and everyone in the street can tell.
A physiotherapist asks a man to stand on his right leg and lift the left foot off the floor. It is the simplest request in medicine. He lifts — and his left hip visibly sags, dropping like one end of a see-saw, and his whole trunk lurches sideways to save him from falling. He has no pain. He is not weak in the leg he is standing on; he can push a car with it. What has failed is a fan-shaped muscle on the side of his hip and the small nerve that feeds it, and their only job was to hold the pelvis level over the standing leg for the half-second the other foot is in the air. That half-second is repeated seven thousand times a day. It is the price of walking on two legs instead of four, and the gluteal region is where the body pays it.
The floor plan: a wall of bone, three layers of muscle
Everything here is built on the outer surface of one bone and aimed at one other. The gluteal region is the mass of soft tissue behind and lateral to the hip joint, filling the space between the iliac crest above and the gluteal fold below. Its back wall is the external surface of the ilium, mapped out by the three gluteal lines described in the hip bone and bony pelvis; its target is the proximal femur, and above all the greater trochanter, the great lateral handle of bone that every abductor grips. Arrange the muscles in layers and the region stops being a jumble. Superficially lie the three big movers — gluteus maximus, gluteus medius and gluteus minimus — together with tensor fasciae latae at the front corner. Deep to them lies a second, smaller band of six short muscles running almost horizontally from the pelvis to the trochanter: the lateral rotators. And running out through the middle of that deep layer, from inside the pelvis into the region and then down the back of the thigh, come the nerves and vessels of the whole limb.
Gluteus maximus: the muscle of climbing, not of walking
Gluteus maximus is the largest and coarsest muscle in the human body, and it takes a remarkably wide origin: the outer surface of the ilium behind the posterior gluteal line, the posterior surface of the lower sacrum and the coccyx, and the sacrotuberous ligament. Its fibres run downwards and laterally at about forty-five degrees, and then — surprisingly — most of them do not reach bone at all. Roughly three-quarters of the muscle inserts into the iliotibial tract, the thickened lateral band of the fascia lata that runs all the way down to the lateral tibial condyle; only the deeper quarter reaches the gluteal tuberosity of the femur. Its actions are powerful hip extension and lateral rotation, with the upper fibres assisting abduction. But here is the fact that catches students out: on level ground, at an ordinary walking pace, gluteus maximus is almost silent. Gravity and momentum do that work. It fires when the demand becomes heavy — climbing stairs, running, rising from a deep chair, standing up out of a squat, sprinting out of the blocks. It is a power reserve, not an everyday engine, and it is supplied by the inferior gluteal nerve (L5, S1, S2).
Medius and minimus: the silent partners of every step
They are called abductors, but their real work is done standing still on one leg. Gluteus medius is a broad fan arising from the outer ilium between the posterior and anterior gluteal lines, converging onto the lateral surface of the greater trochanter. Gluteus minimus lies directly underneath it, arising between the anterior and inferior gluteal lines and inserting onto the anterior surface of the same trochanter. Both abduct the hip, and their anterior fibres medially rotate it — a point worth pausing on, because the region's deep layer does the exact opposite. Both are supplied by the superior gluteal nerve (L4, L5, S1). Their headline function, though, is not moving the leg outwards at all; it is stabilising the pelvis. When you lift one foot, the whole weight of the body hangs on the far side of the hip joint on the standing leg, and it would tip the pelvis down towards the swinging leg like a loaded see-saw. Medius and minimus on the STANDING side contract and pull the ilium down towards the trochanter, holding the pelvis level — or even lifting the free side slightly so the swinging foot can clear the floor. Tensor fasciae latae joins the effort from the front, arising from the anterior superior iliac spine and inserting into the iliotibial tract; it too is a superior gluteal nerve muscle, and it stiffens the tract so that gluteus maximus and the abductors pull on a taut cable rather than a slack one.
Picture a construction crane. The tower is your standing leg, the horizontal jib is your pelvis, and the load swinging at the end of the jib is the entire weight of your body plus the leg dangling in the air. A crane cannot hold a load out to one side without a counterweight on the opposite arm — and gluteus medius is that counterweight, pulling down on the near side of the pelvis with just enough force to keep the jib horizontal. Now cut the counterweight cable. The jib does not stay level and swing gently; it drops on the far side, exactly as the pelvis drops on the unsupported side in the Trendelenburg sign. And notice which side fails: the cable that snapped is on the leg you are standing on, but the end that falls is the other one.
The Trendelenburg sign — and the injection quadrant
This is the clinical spine of the whole region, and it is worth stating with painful precision. If the superior gluteal nerve is damaged, or gluteus medius itself fails, then when the patient stands on the AFFECTED leg the pelvis DROPS on the CONTRALATERAL, unsupported side. The lesion is on the standing side; the sag appears on the swinging side. To keep the swinging foot from scraping the floor the patient throws the trunk sideways over the affected hip with each step, and if both sides are involved the result is the rolling, side-to-side waddling gait. From this one piece of anatomy comes one of the most repeated safety rules in clinical practice. The superior gluteal nerve leaves the pelvis into the upper part of the region, and the sciatic nerve — the thickest nerve in the body — runs down through the lower and medial part. An intramuscular injection must therefore be placed in the UPPER OUTER QUADRANT of the buttock, where there is thick muscle and no major nerve. Aim low or medial and the needle finds the sciatic nerve; aim carelessly high and medial and you risk the superior gluteal nerve, and you may hand the patient a permanent Trendelenburg gait in exchange for an injection they could have had elsewhere.
The deep six: the lateral rotators
Small, short, horizontal — the rotator cuff of the hip. Lift gluteus maximus away and a neat row of short muscles appears, running almost horizontally from the pelvis to the greater trochanter. From top to bottom they are: piriformis, arising from the anterior surface of the sacrum and leaving the pelvis through the greater sciatic foramen to insert on the upper border of the greater trochanter; obturator internus, arising from the inner surface of the obturator membrane and its bony margin, turning through ninety degrees around the lesser sciatic notch like a rope over a pulley; the superior and inferior gemelli, two small slips arising from the ischial spine and ischial tuberosity respectively that flank the obturator internus tendon and insert with it into the medial surface of the greater trochanter; quadratus femoris, a flat quadrilateral running from the lateral border of the ischial tuberosity to the quadrate tubercle on the intertrochanteric crest; and, deepest of all, obturator externus, from the outer surface of the obturator membrane to the trochanteric fossa. All of them laterally rotate the extended hip and help hold the femoral head firmly in the acetabulum — which is precisely the role the rotator cuff plays at the shoulder, only here the joint they steady is built for stability rather than range. Their innervation comes from small branches of the sacral plexus (nerve to obturator internus L5–S2, nerve to quadratus femoris L4–S1), except obturator externus, which belongs to the obturator nerve.
Piriformis: the key to the whole region
Anatomists describe the gluteal region the way sailors describe a coastline: by one landmark, with everything else placed above it or below it. That landmark is piriformis. It fills the greater sciatic foramen as it passes out of the pelvis, and every nerve and vessel that uses that doorway is defined by whether it emerges above the muscle or below it. ABOVE piriformis pass only the superior gluteal nerve and the superior gluteal vessels — which is why they lie high in the buttock, and why the upper outer quadrant is safe from the sciatic but not from them. BELOW piriformis pass everything else: the inferior gluteal nerve and vessels to gluteus maximus; the sciatic nerve, as thick as a finger, heading for the back of the thigh and described in full in the sciatic, tibial and common fibular nerves; the posterior cutaneous nerve of the thigh; the nerve to quadratus femoris; and the pudendal nerve with the internal pudendal vessels. Those last two do something unusual — they emerge below piriformis, hook around the ischial spine and the sacrospinous ligament, and immediately re-enter the pelvis through the LESSER sciatic foramen to reach the perineum. All of these are terminal offshoots of the great network described in the lumbosacral plexus, and the greater sciatic foramen is the single door through which the plexus reaches the limb.
There is a beautiful symmetry hiding in this region: the superficial layer medially rotates and the deep layer laterally rotates, and the two are wired by different nerves so that they can be lost independently. Gluteus medius and minimus (superior gluteal nerve) abduct and MEDIALLY rotate; the deep six laterally rotate. Gluteus maximus straddles both worlds — a lateral rotator and the most powerful extensor you own. And here is the wonder of it: because gluteus maximus barely works on level ground, a person can lose the inferior gluteal nerve entirely and still walk across a room looking almost normal. Ask them to climb one flight of stairs, or to stand up from a low sofa without using their hands, and the loss appears instantly. Function reveals what a resting examination hides — the same lesson that runs through all of muscle and movement.
The sprinter: look at the build of any elite 100 m runner and the glutes are enormous. Sprinting is repeated, violent hip extension from a deeply flexed start position — exactly the movement gluteus maximus was built for — which is why a distance runner and a sprinter, both athletes, are shaped so differently. The stairs test: an elderly patient walks into clinic without a limp, then grips the banister with both hands to climb three steps. Level walking hides a weak gluteus maximus; a staircase interrogates it. Deep gluteal (piriformis) syndrome: a taxi driver sits for ten hours a day on a wallet-thick edge of seat and develops a deep, aching buttock pain that radiates down the back of the thigh and worsens with sitting — the sciatic nerve irritated where it passes beneath a tight piriformis, mimicking a disc prolapse but with a normal back. Trochanteric bursitis: a woman who has just increased her running distance develops sharp pain on the point of the hip, worse lying on that side at night — the bursa between the iliotibial tract and the greater trochanter, inflamed by the tract sliding over bone thousands of times a day, and often treated with the NSAIDs that damp that inflammation.
- Gluteus maximus: ilium behind the posterior gluteal line + sacrum + coccyx + sacrotuberous ligament → mostly the ILIOTIBIAL TRACT, partly the gluteal tuberosity.
- Maximus extends and laterally rotates the hip — used for climbing, running and rising from sitting, NOT for level walking; inferior gluteal nerve (L5–S2).
- Gluteus medius and minimus: outer ilium → greater trochanter; abduct and MEDIALLY rotate; superior gluteal nerve (L4–S1).
- Their key role is PELVIC STABILISATION in single-leg stance — they hold the pelvis level while the other foot swings through.
- Tensor fasciae latae: ASIS → iliotibial tract; superior gluteal nerve; tightens the tract so the abductors pull on a taut band.
- TRENDELENBURG: superior gluteal nerve or gluteus medius failure → standing on the AFFECTED leg drops the pelvis on the CONTRALATERAL side.
- The deep lateral rotators, top to bottom: piriformis, obturator internus with superior and inferior gemelli, quadratus femoris, obturator externus.
- PIRIFORMIS is the landmark: it exits the greater sciatic foramen, and everything else in the region is described as above or below it.
- ABOVE piriformis: the superior gluteal nerve and superior gluteal vessels — and nothing else.
- BELOW piriformis: the inferior gluteal nerve and vessels, the SCIATIC nerve, the posterior cutaneous nerve of the thigh, the nerve to quadratus femoris, and the pudendal nerve with the internal pudendal vessels.
- The pudendal nerve and internal pudendal vessels re-enter the pelvis through the LESSER sciatic foramen to reach the perineum.
- Intramuscular injections go in the UPPER OUTER QUADRANT of the buttock — thick muscle, and clear of the sciatic nerve below and medial.
- Getting the side wrong in the Trendelenburg sign. The DAMAGED side is the one being stood on; the pelvis sags on the OPPOSITE, unsupported side. Saying "the hip drops on the injured side" is the single commonest error in this topic.
- Believing gluteus maximus is the muscle of walking. On level ground it is nearly silent — it is the muscle of stairs, hills, sprinting and standing up. The abductors, not the extensor, are what walking really depends on.
- Assuming all the gluteal muscles rotate the hip the same way. The superficial medius and minimus MEDIALLY rotate; the deep six and gluteus maximus LATERALLY rotate. The layers pull in opposite directions.
A patient stands on the right leg and lifts the left foot; the left side of the pelvis drops. Which nerve is most likely damaged, and on which side?
- Gluteus maximus (ilium behind the posterior gluteal line, sacrum, coccyx, sacrotuberous ligament → iliotibial tract and gluteal tuberosity; inferior gluteal nerve) extends and laterally rotates the hip — for stairs, running and standing up, not level walking.
- Gluteus medius, minimus and tensor fasciae latae (superior gluteal nerve) abduct, medially rotate and above all STABILISE THE PELVIS in single-leg stance.
- Trendelenburg sign: with a failed superior gluteal nerve or gluteus medius, standing on the affected leg drops the pelvis on the CONTRALATERAL side — hence the waddling gait, and hence the upper outer quadrant injection rule.
- Piriformis is the landmark of the greater sciatic foramen: above it only the superior gluteal nerve and vessels; below it the inferior gluteal nerve and vessels, the sciatic nerve, the posterior cutaneous nerve of the thigh, the nerve to quadratus femoris and the pudendal neurovascular bundle.
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students — Lower limb: the gluteal region.
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy — Gluteal region, Trendelenburg sign and safe intramuscular injection.
- Netter FH. Atlas of Human Anatomy — Muscles and nerves of the gluteal region.
- Last RJ. Last's Anatomy: Regional and Applied — The gluteal region and the greater sciatic foramen.
- Snell RS. Clinical Anatomy by Regions — The buttock: deep gluteal syndrome and injection safety.
- TeachMeAnatomy — Muscles of the Gluteal Region; The Sciatic Nerve.
