Do Butts Have Bones? The Anatomy of the Gluteal Region

Your butt cheeks themselves contain no bones, but the gluteal region sits directly on top of several important ones. The fleshy roundness you can grab is mostly muscle and fat layered over the pelvis, sacrum, coccyx, and the tops of the femurs. Understanding what is actually in there helps explain everything from why sitting too long hurts to why your glutes matter so much for movement, and why certain medical procedures in the area carry real risks.

The Bones You Are Sitting On

When you sit down, your weight does not rest on muscle or fat alone. It funnels through your skeleton to two bony knobs at the base of each side of the pelvis called the ischial tuberosities. You can feel them if you sit on a hard surface and shift your weight. These are the “sit bones,” and they are the main skeletal landmarks of the gluteal region. Above them, the broad wings of the ilium (the bones you feel when you put your hands on your hips) form the upper border of the buttocks. Behind them, the sacrum and coccyx (tailbone) sit at the midline where the spine meets the pelvis.

The ischial tuberosities matter more than most people realize. When you sit, the soft tissue between these bony prominences and the chair compresses under load. Sustained compression of the tissue beneath the ischial tuberosities is the primary mechanism behind deep tissue injury of the buttocks, the kind that leads to pressure sores in people who sit or lie in one position for extended periods.¹ Research on sitting biomechanics has found that internal muscle tissue loads under the ischial tuberosities are lowest in people with a low-normal body mass index, and elevated at both very high and very low BMIs.² In other words, both being significantly underweight and significantly overweight increases the mechanical stress on buttock tissues when you sit.

The coccyx, though small, is another source of trouble. Tailbone pain, called coccygodynia, is common in women with pelvic pain. A study of 127 women with pelvic pain found that about half had coccygodynia, and those who did were significantly more likely to have muscle spasm in the surrounding pelvic floor, higher pain scores, and impaired coordination of their pelvic floor muscles.³ So while the coccyx is tucked away at the very base of the spine, it can create radiating buttock and pelvic discomfort when it becomes irritated or hypomobile.

The femur also plays a role. The greater trochanter, the bony bump you can feel on the outer side of your upper thigh, is where several gluteal muscles attach. It sits just below and to the side of the buttock proper, and pain around it is one of the most common complaints people describe as “hip pain” when the problem is actually in the gluteal tendons wrapping around it.

The Three Gluteal Muscles

The bulk of your butt is muscle, and three muscles dominate the region. The gluteus maximus is the largest and most powerful muscle in the human body.⁴ It is the one you can feel contracting when you climb stairs, stand up from a chair, or sprint. It covers almost the entire back of the pelvis and gives the buttock its distinctive rounded shape.

Beneath the gluteus maximus lie the gluteus medius and gluteus minimus, which are smaller and fan-shaped. They originate on the outer surface of the ilium and insert on the greater trochanter of the femur. Their primary job is not to push you forward but to keep you from falling sideways. The gluteus medius stabilizes the hip during the first phase of each step you take, while the gluteus minimus takes over stabilization during mid- and late stance.⁵ Without them, your pelvis would drop on the unsupported side every time you lifted a foot off the ground.

An interesting finding from research on healthy adults is that the thickness of the gluteus medius and minimus, as measured by ultrasound, does not correlate well with hip abductor strength or functional performance.⁶ A thicker muscle on imaging does not necessarily mean a stronger one. This is a reminder that muscle architecture, neuromuscular activation patterns, and training all matter as much as raw size.

The Deep Rotators Hidden Underneath

Below the three gluteal muscles lies a group of smaller muscles that most people have never heard of: the deep external rotators of the hip. These include the piriformis, the obturator internus, the superior and inferior gemelli, and the quadratus femoris. They sit in the subgluteal space, essentially wedged between the back of the hip joint and the gluteus maximus above them.

These muscles rotate your thigh outward and help stabilize the hip joint during movement. They are small, but they are clinically significant because major nerves and blood vessels thread through the same cramped space. The sciatic nerve, the largest nerve in the body, passes through or near the piriformis on its way down the back of the thigh. When any of the structures in this region become irritated, scarred, or swollen, the sciatic nerve can get pinched. This condition is called deep gluteal syndrome, an umbrella diagnosis that goes well beyond the old label of “piriformis syndrome.” Deep gluteal syndrome can involve fibrous bands, problems with the obturator internus or gemellus muscles, quadratus femoris pathology, hamstring conditions, and other causes of sciatic nerve entrapment in the subgluteal space.⁷

Ultrasound imaging has shown that the deep rotators can be reliably visualized, which is useful for both diagnosis and guided injections. Studies rating the visibility of these muscles on dynamic ultrasound have found that the piriformis, obturator internus, inferior gemellus, and quadratus femoris are generally well seen, while the superior gemellus can be slightly harder to distinguish.⁸

The Fat Layer and Why It Varies So Much

On top of the muscle sits the subcutaneous fat layer, which is responsible for much of the variation in buttock shape and size between individuals. This fat is not inert padding. It is metabolically active tissue with its own hormonal profile. Research comparing gluteal fat to abdominal fat in premenopausal women found that the two depots express estrogen receptors differently. Gluteal fat had higher levels of estrogen receptor beta (ERβ) protein, while abdominal fat had higher levels of estrogen receptor alpha (ERα) and a higher ERα-to-ERβ ratio.⁹ This hormonal difference helps explain why fat tends to accumulate on the buttocks and thighs in women under the influence of estrogen, creating the characteristic “pear-shaped” fat distribution pattern, and why fat distribution shifts after menopause when estrogen levels fall.

The thickness of the fat layer also influences how comfortable you are when sitting and how vulnerable you are to pressure injuries. People with very little gluteal fat have less cushioning over their ischial tuberosities, which is part of why the biomechanical research mentioned earlier found elevated tissue loads in people at the low end of the BMI range. There is a Goldilocks zone: enough fat to pad the bones, but not so much that the tissue mechanics become unfavorable.

Why Humans Have Uniquely Large Glutes

If you have ever wondered why human buttocks are so much more prominent than those of other primates, the answer has less to do with sitting and more to do with running. The gluteus maximus does surprisingly little work during normal walking. Its primary role activates during running, sprinting, and climbing. Research on the evolutionary biomechanics of the muscle supports the idea that enlargement of the gluteus maximus was likely important in the evolution of hominid running capabilities rather than walking.¹⁰

Comparative anatomy bears this out. In great apes, the gluteus maximus is relatively small and structured differently. A study comparing hindlimb muscle architecture across apes and humans found that ape gluteal anatomy follows a different pattern, with the gluteus maximus often partially separated into distinct portions and a comparatively weaker tensor fascia lata.¹¹ The way the gluteus maximus attaches to the femur also tells an evolutionary story. Research using imaging to compare the musculoskeletal anatomy of the proximal femur in humans and great apes found that chimpanzees and humans share a similar arrangement of where the gluteus maximus inserts relative to other thigh muscles, while gorillas and orangutans show a more primitive configuration.¹²

The upshot is that your large, rounded gluteus maximus is one of the defining anatomical features of being human. It enabled endurance running, which was likely critical for persistence hunting and long-distance travel across open landscapes. Other primates simply do not need that much power at the hip, because they do not run the way we do.

When the Gluteal Region Hurts

Buttock pain has a surprisingly long list of possible causes, and the anatomy of the region explains why. With bones, large muscles, deep rotator muscles, thick fat, major nerves, and several bursae all packed into a relatively small area, there are many structures that can go wrong.

One of the most common culprits is tendinopathy of the gluteus medius and minimus where they attach to the greater trochanter. MRI studies have shown that tears and degeneration of these tendons are a frequent cause of lateral hip and buttock pain, and are probably responsible for much of what has traditionally been called “trochanteric bursitis.”¹³ The anterolateral portion of the gluteus medius tendon is particularly vulnerable to tears because it has a thin tendinous section.¹⁴

Deep gluteal syndrome, as described earlier, is another major source of pain that often goes undiagnosed for years. Patients typically report aching or burning in the buttock that can radiate down the back of the leg, mimicking a herniated disc. And gluteus maximus weakness or inhibition, which can develop from prolonged sitting or injury, contributes to chronic low back pain, hip pain, and reduced athletic performance.⁴

How Your Glutes Connect to Your Back

The gluteal region does not work in isolation. The gluteus maximus connects to the thoracolumbar fascia, a dense sheet of connective tissue that spans the lower and mid back. Through this fascial network, the gluteus maximus on one side of the body has a mechanical link to the latissimus dorsi muscle on the opposite side. This cross-body connection creates a diagonal sling that transfers force between the upper body and the lower body during movements like walking and throwing.

When this connection breaks down, the consequences can show up far from the buttock. A study comparing people with chronic low back pain to healthy controls found that contracting the latissimus dorsi increased lumbar stiffness in both groups. But only in the healthy group did that contraction also change the resting position and passive torque at the opposite hip, indicating force was being transmitted through to the gluteus maximus. In people with chronic low back pain, that transmission was absent: the force stayed local in the lumbar region and did not reach the distant tissues.¹⁵ This is one reason why rehabilitation for chronic back pain often includes gluteal strengthening: restoring the mechanical partnership between the glutes and the trunk matters for how the whole system distributes load.

Injections and Surgical Risks in the Region

The complex anatomy of the gluteal region makes it a consequential area for medical procedures. For decades, the upper outer quadrant of the buttock (the dorsogluteal site) was the default location for intramuscular injections. This practice has fallen out of favor in many clinical guidelines because of the risk of hitting the sciatic nerve or the superior gluteal artery. Research on safe injection sites has highlighted the middle of the vastus lateralis in the thigh as a preferable alternative due to the low risk of vascular or nerve damage in that area.¹⁶ When the gluteal region is used for injections, the ventrogluteal site (further forward on the hip, over the gluteus medius) is now considered safer than the dorsogluteal site.

The stakes are even higher in cosmetic surgery. The Brazilian butt lift, in which fat is harvested from one area of the body and injected into the buttocks, has become one of the most popular cosmetic procedures worldwide, but it also carries a serious risk. Fat emboli, where injected fat enters blood vessels and travels to the lungs, are a potentially fatal complication that has been specifically linked to intramuscular injection of fat into the gluteus maximus.¹⁷ The gluteal region is rich in large veins, and injecting fat deep into the muscle rather than the subcutaneous layer increases the chance that fat globules enter the venous system. This has prompted surgical societies to issue guidelines recommending that fat be placed in the subcutaneous tissue only, avoiding the muscle layer entirely.

The anatomy that makes the buttock look simple on the outside, a rounded mound of soft tissue, actually makes it one of the more treacherous regions for a surgeon or clinician to work in. Large nerves, large blood vessels, multiple muscle layers, and variable fat thickness all create a landscape where precision matters enormously.

What “Dead Butt Syndrome” Actually Is

You may have seen headlines about “dead butt syndrome,” a colloquial name for gluteal amnesia or gluteus medius tendinopathy aggravated by prolonged sitting. The idea is that spending hours in a chair causes the gluteal muscles to stop firing properly, essentially “forgetting” how to activate. While the catchy name overstates the case, the underlying concern has some anatomical basis. Sitting for long periods keeps the hip flexors shortened and the glutes lengthened, which over time can alter neuromuscular activation patterns. The gluteus maximus is known to be prone to inhibition and weakness, which contributes to chronic pain and injury.⁴

The fix is not complicated: regular movement, hip extension exercises like bridges and lunges, and avoiding sitting for hours without a break. The gluteal muscles respond well to targeted strengthening. For people with genuine tendinopathy of the gluteus medius or minimus, rehabilitation programs that progressively load the tendons are typically the first-line treatment before anyone considers imaging or injection.

So while your butt cheeks contain no bones of their own, the region is far from simple. It is a layered stack of bone, deep stabilizers, large power muscles, metabolically active fat, major nerves, and fascial connections that reach all the way up to the opposite shoulder. The bones are hidden underneath, but they shape everything about how the region works, how it can go wrong, and why it deserves more anatomical respect than most people give it.