The pelvic girdle is a ring of bones at the base of your trunk that connects your spine to your legs. It’s made up of three fused bones on each side (the ilium, ischium, and pubis) joined at the front by a cartilage joint and at the back by the sacrum. Together, these structures bear your full upper-body weight, anchor some of the strongest muscles in your body, and protect the organs sitting deep inside your lower abdomen.
Bones That Make Up the Pelvic Girdle
Each side of the pelvic girdle starts as three separate bones that gradually fuse together during childhood and adolescence. By adulthood they form a single unit called the hip bone, but each part has a distinct shape and job.
The ilium is the largest of the three. It’s the broad, curved bone you feel when you put your hands on your hips. Its wide surface provides attachment points for the muscles of your core and thighs. The ischium hangs from the bottom of the hip bone in a U-shape and forms the bony part of your buttocks, which is why it’s often called your “sit bone.” The pubis is the smallest piece on each side. Your two pubic bones meet at the front of the pelvis at a joint called the pubic symphysis, completing the ring.
Behind the girdle sits the sacrum, a spade-shaped bone formed by the last five vertebrae of the spine fusing together (a process that isn’t finished until puberty). Below the sacrum is the coccyx, or tailbone. While these two bones are technically part of the spine, they lock into the back of the pelvic ring and are essential to its structure.
Key Joints and How They Hold Together
Three joints keep the pelvic girdle stable while still allowing a small amount of movement. At the front, the pubic symphysis connects the left and right pubic bones with a disc of tough cartilage. This joint absorbs shock during activities like running and walking, and ligaments hold it firmly in place so the two sides of the pelvis can’t shift unevenly.
At the back, two sacroiliac joints link the sacrum to the left and right ilium. These joints carry the full load of your trunk. The surfaces of the sacroiliac joints are oriented along the direction of that downward force, which means they experience significant shear stress. A dense web of ligaments surrounds each joint to keep the sacrum locked in place under load. The hip joints, where each side of the pelvis meets the thigh bone, are technically separate from the pelvic girdle itself, but they depend entirely on the girdle for their socket.
How the Pelvic Girdle Transfers Weight
Every time you stand, walk, or lift something, the weight of your head, arms, and trunk travels down through your spine and into the sacrum. From there it passes through the sacroiliac joints into the hip bones and then down through the hip sockets into your legs. In an upright standing position, roughly 500 newtons of trunk load (the equivalent of about 110 pounds in an average adult) passes through this pathway. Abdominal muscles, pelvic ligaments, and the vertical shear forces at the sacroiliac joints all work together to balance that load so no single structure is overwhelmed.
This weight-transfer role is the reason the pelvic girdle is so much thicker and more rigid than the shoulder girdle. Your shoulder blades can glide freely because your arms don’t bear your body weight. Your pelvis can’t afford that kind of mobility, so it trades range of motion for strength.
Muscles Anchored to the Pelvis
Some of the most powerful muscles in the body originate on the pelvic girdle. The gluteal group (gluteus maximus, medius, and minimus) attaches across the outer surface of the ilium and drives hip extension, the motion that propels you forward when you walk or push you upright from a squat. The gluteus maximus is one of the largest muscles in the human body.
On the inner side, the iliopsoas group (the psoas major and iliacus) connects the pelvis and lower spine to the thigh bone and acts as the primary hip flexor, pulling your knee upward. The adductor group lines the inner thigh and draws the leg inward, while a set of six small deep rotators, including the piriformis, sit beneath the glutes and rotate the thigh outward. Nearly every muscle that moves the thigh bone originates somewhere on the pelvic girdle.
At the bottom of the pelvic ring, the pelvic floor muscles (primarily the levator ani and coccygeus) stretch like a hammock from the pubis to the coccyx. These muscles support the bladder, intestines, and reproductive organs from below and play a central role in continence and core stability.
Organs the Pelvis Protects
The bony ring of the pelvis creates a sheltered cavity for organs that would otherwise be vulnerable. The bladder sits just behind the pubic symphysis. The lower portion of the large intestine, including the rectum, passes through the pelvic cavity on its way to the anal canal. In people with female anatomy, the uterus, ovaries, and fallopian tubes occupy the center of the pelvic space, and the birth canal passes directly through the pelvic opening. In people with male anatomy, the prostate gland sits at the base of the bladder within the same protected space.
Differences Between Male and Female Pelves
The pelvis is one of the most sexually dimorphic bones in the skeleton, meaning its shape differs noticeably between males and females. A female pelvis is generally wider and shallower, with a broader pelvic inlet (the opening at the top of the pelvic cavity) to accommodate childbirth. The subpubic angle, the angle formed where the two pubic bones meet at the front, is wider in females (typically around 80 to 85 degrees or more) compared to the narrower, more V-shaped angle in males (closer to 50 to 60 degrees). The sacrum also tends to be shorter and less curved in females. These differences emerge during puberty as hormonal changes reshape the growing bone.
Pelvic Girdle Pain
Pelvic girdle pain is most commonly associated with pregnancy, affecting somewhere between 23% and 65% of pregnant women depending on how the condition is measured. It typically shows up as deep aching near the sacroiliac joints, across the back of the pelvis, or around the pubic symphysis. The cause is multifactorial: hormonal changes that loosen ligaments, increased mechanical load, and shifts in posture all contribute.
The good news is that about 78% of women recover spontaneously within six weeks after delivery. However, roughly one-third still have symptoms at three months postpartum, and about 8.5% report significant pain two years later. Outside of pregnancy, pelvic girdle pain can also result from trauma, arthritis, or degenerative joint changes at the sacroiliac joints.
Pubic symphysis dysfunction is a related condition in which the joint at the front of the pelvis becomes too mobile or inflamed. The ligaments that normally hold it in place loosen, allowing the pelvic bones to shift unevenly. This creates a grinding or clicking sensation and sharp pain with activities like walking, climbing stairs, or rolling over in bed.