The pelvis is a basin-shaped group of bones that sits between your lower spine and your legs, forming the structural bridge between your upper and lower body. It carries the weight of everything above it, protects several vital organs, and anchors the muscles that let you walk, run, and stand upright. Despite being talked about as one structure, the pelvis is actually made up of several bones fused and joined together.
Bones That Make Up the Pelvis
The pelvis consists of two hip bones, one on each side, along with the sacrum and coccyx (tailbone) at the back. Each hip bone is itself formed from three smaller bones that fuse together during adolescence: the ilium, ischium, and pubis. The ilium is the broad, wing-shaped bone you can feel at your waist when you put your hands on your hips. The ischium is the lower, rear portion, the bone you’re sitting on right now. The pubis forms the front of the pelvis, where the two hip bones meet at a joint called the pubic symphysis.
The sacrum, a triangular bone at the base of the spine, wedges between the two hip bones at the back. Below it hangs the coccyx, a small set of fused vertebrae. Together, these bones form a ring-like structure that is remarkably strong, designed to handle the constant stress of bearing your body’s weight while still allowing a range of motion at the hip joints.
What the Pelvis Does
The pelvis serves three major roles. First, it is a load-bearing structure. Every time you stand, walk, or run, the weight of your head, torso, and arms transfers through your spine into the sacrum, across the hip bones, and down into your legs. The arrangement of bones and ligaments within the pelvis distributes these forces efficiently enough to handle the repeated impact of activities like running and jumping.
Second, the pelvis protects internal organs. The bony ring acts as a shield around the bladder, rectum, and the lower portion of the large intestine. In women, it also encloses the uterus, fallopian tubes, and ovaries. These organs sit within the pelvic cavity, sometimes called the “true pelvis,” which is the deeper, bowl-shaped space enclosed between the pelvic inlet (the upper rim) and the pelvic outlet (the lower opening).
Third, the pelvis is an anchor point for dozens of muscles. The muscles of your thighs, buttocks, lower back, and abdomen all attach to various surfaces of the pelvic bones. Without these attachment points, movements as basic as walking or bending forward wouldn’t be possible.
The Pelvic Floor
Stretched across the bottom opening of the pelvis is a hammock-like layer of muscles known as the pelvic floor. These muscles are organized into superficial and deep layers. The deeper muscles span from the pubic bone to the tailbone, creating a physical “floor” that holds the bladder, rectum, and (in women) the uterus in place against the pull of gravity.
Beyond support, these muscles also control continence. One key muscle loops around the anal canal, vagina, and urethra, compressing them against the back of the pubic bone when it contracts. This is what allows you to hold your bladder or bowel when you need to. When the pelvic floor weakens, whether from childbirth, aging, or chronic strain, problems like incontinence or organ prolapse can develop.
Differences Between Male and Female Pelves
The pelvis is one of the most sexually dimorphic bones in the human skeleton, meaning its shape differs noticeably between males and females. The male pelvis is generally heavier and thicker, with a narrower overall shape. The female pelvis is wider and shallower, with a larger pelvic inlet and outlet. These proportions create the space needed for childbirth.
One of the clearest differences is the subpubic angle, the V-shaped arch beneath the pubic symphysis. In females, this angle is close to 90 degrees. In males, it is roughly 30 degrees narrower, creating a more acute angle. The notch at the back of each hip bone is also broader in females. These distinctions are reliable enough that forensic scientists routinely use the pelvis to determine sex from skeletal remains.
How the Pelvis Shaped Human Walking
The human pelvis looks dramatically different from that of other great apes, and those differences are directly tied to walking upright. In apes, the ilium is tall and narrow, oriented toward the back. In humans, the ilium became shorter from top to bottom, wider from front to back, and curved along the sides of the body. This reshaped the pelvis into the familiar bowl shape, which does two critical things: it positions the gluteal muscles to stabilize the hip during each step, and it cradles the internal organs that would otherwise press downward against gravity in an upright posture.
This adaptation also created a tradeoff. A wider, bowl-shaped pelvis supports bipedal walking but narrows the birth canal relative to the size of a human infant’s head. This is one reason human childbirth is more difficult than in other primates.
Common Pelvic Injuries
Pelvic ring injuries account for about 3% of all skeletal fractures and occur across all age groups. In younger people, they typically result from high-energy events like car accidents or falls from height. In older adults, even a low-energy fall can fracture the pelvis, especially when bone density has declined.
The severity varies enormously. A small, stable crack in the pubic bone or sacrum may heal with rest and pain management. A high-energy disruption that breaks the pelvic ring in multiple places is a medical emergency, often involving significant internal bleeding. Mortality rates range from 1% to 15% for closed fractures but can reach 50% for open fractures, with hemorrhage being the leading cause of death.
Even after healing, pelvic fractures can have lasting consequences. Roughly 39% of certain sacral fractures managed without surgery shift out of alignment over time, and that number climbs to 68% when fractures occur on both sides. Sexual dysfunction is also common: erectile dysfunction occurs in 46% of males after a pelvic ring injury, and painful intercourse affects 56% of females. Nerve damage involving the lower spinal nerve roots occurs in about half of fractures through a particular zone of the sacrum.