Pelvis: Anatomy, Bones, Function, Shapes and Common Conditions

Medically reviewed by *Dr. Baraa Alnahhal, MD* · Last reviewed: October 2026

Quick Answer

The pelvis is a bony basin at the base of the spine. It sits inside the hips, buttocks and pubic region, supports the trunk and connects the upper body to the legs. Its cavity holds urinary and reproductive organs, and its central opening serves as the birth canal during vaginal delivery. [1]

Core idea	Plain-language meaning
Structure	A bony basin at the base of the spine.
Location	Inside the hips, buttocks and pubic region.
Main support role	Helps carry the upper body when sitting, standing or walking.
Connection	Links the trunk with the legs.
Pelvic cavity	Space that holds urinary and reproductive organs.
Opening	Serves as the birth canal during vaginal delivery.

The pelvis supports the trunk and connects the upper body with the legs.

What the research says

• Pelvic shape varies a great deal. A review of birth-canal variation found that the human birth canal is highly variable within and among populations, and that the common obstetric model of “normal” labour reflects a pelvic shape that is common in European women. As a result, pelvic shape and labour patterns in other women are more likely to be judged abnormal (Betti, Philos Trans R Soc Lond B Biol Sci, 2021). [2]

• Evidence for rehabilitation after pelvic fragility fractures is limited. A scoping review of 17 studies in adults aged 60 and over found that 13 described only mobilisation strategies (9 cited unrestricted mobilisation first), that 31 outcome domains (such as pain, mobility, activities of daily living, quality of life and mortality) were reported, and that there was no consensus on which patient-reported outcome instruments to use (Carter et al., Osteoporos Int, 2025). [3]

What does the pelvis do?

The pelvic bones support the weight of the upper body together with the muscles of the pelvic floor. This support matters when you sit, stand or walk. [1]

The pelvic cavity, the space between the pelvis and abdomen, holds urinary and reproductive organs. The opening in the pelvis serves as the birth canal during vaginal delivery. [1]

The word “pelvis” can also describe the broader pelvic region between the abdomen and thighs. Pain in this region may involve organs inside the space, including the urinary system, reproductive system, rectum or anus. A pelvic exam generally examines these organs. Read more in our guide to chronic pelvic pain.

Pelvic role	What it involves
Weight bearing	Supports the upper body with help from the pelvic-floor muscles.
Movement	Connects the trunk with the legs and contributes to sitting, standing and walking.
Protection and containment	The pelvic cavity holds urinary and reproductive organs.
Childbirth	The central opening serves as the birth canal during vaginal delivery.

Which bones make up the pelvis?

Five separate bones combine to form the bony pelvis: the sacrum, coccyx, ilium, ischium and pubis. The ilium, ischium and pubis form the pelvic girdle around the pelvic spine. [1]

Sacrum

The sacrum is a spade-shaped bone at the base of the spine. It forms when five vertebrae at the base of the spine fuse together, a process that is usually complete by early adulthood.

Coccyx

The coccyx is the tailbone, the small final bone at the tip of the spine and sacrum. The sacrum and coccyx together may be called the pelvic spine. [1]

Ilium

The ilium is the largest pelvic-girdle bone. It is broad and concave, and it wraps around the sides of the hips. [1]

Ischium

The ischium, or ischia when referring to both sides, forms the two “sit bones.” These U-shaped bones hang from the base of the pelvic girdle and form the bony part of the buttocks. [1]

Pubis

The pubis, or pubic bone, is the smallest bone on each side of the pelvis. The two pubic bones meet at the front and center at a joint called the pubic symphysis. [1]

The five bones of the bony pelvis and their relationship to the pelvic spine and pelvic girdle.

Bone	Description
Sacrum	Spade-shaped bone at the base of the spine, formed as five vertebrae fuse.
Coccyx	Tailbone and final small bone at the tip of the spine and sacrum.
Ilium	Largest pelvic-girdle bone; broad, concave and wrapped around the hips.
Ischium	The paired “sit bones” forming the bony buttocks.
Pubis	Smallest bone on each side; the two sides meet at the pubic symphysis.

The ilium, ischium and pubis are separate bones during childhood and fuse during puberty. [1]

What are the important pelvic joints?

A joint is where two bones meet. Small joints between the vertebrae of the pelvic spine help the spine move. Other joints connect the pelvic-girdle bones to each other and to the rest of the body. Cartilage and ligaments help hold the joints together. [1]

Joint	Where it is or what it connects
Sacrococcygeal joint	Connects the sacrum to the coccyx below.
Lumbosacral joints	Connect the lumbar spine with the sacrum.
Pubic symphysis	Joint between the two pubic bones at the front of the pelvis.
Sacroiliac joints	Connect each ilium to the sacrum.
Hip joints	Connect the thigh bones to the pelvis at sockets called the acetabula, formed where the ilium, ischium and pubis meet.

What are the four traditional pelvis shapes?

Historically, healthcare professionals described four basic pelvis shapes: android, anthropoid, gynecoid and platypelloid. Current understanding recognizes pelvic shapes as a spectrum rather than four rigid categories. The traditional types mainly differ in the shape of the pelvic opening at the top, called the inlet. [1]

Traditional term	Description
Android	Roughly heart-shaped, with a conical or wedge-shaped opening; wider at the inlet and narrower toward the outlet.
Anthropoid	Narrower than some other types and deeper than wide, with an oval opening.
Gynecoid	Rounder, with wide hips and a wide, round opening; associated with the easiest vaginal delivery.
Platypelloid	Least common of the four; wide and shallow, with pronounced hips and a flat front and back.

Pelvic shape descriptions are reference categories, not a complete account of every person’s anatomy. Pelvic shapes vary widely, and all types can deliver healthy babies.

How can pelvic anatomy differ by reproductive anatomy?

The pelvis continues to grow and change through puberty. By adulthood, pelvic anatomy differs in some ways according to the reproductive organs a person has. These differences relate to childbirth and to walking or running on two feet. [1]

A pelvis associated with a female reproductive system is described as broader and shallower, with a larger inlet. The ischia are farther apart, the outlet and pubic arch are wider, the acetabula are farther apart and angled inward, the sacrum is shorter and wider, and the coccyx is movable. [1]

A pelvis associated with a male reproductive system is described as taller, narrower and more compact. It narrows from top to bottom, has a narrower pubic arch, acetabula that are closer together and angled outward, a longer and narrower sacrum, and a coccyx angled inward that does not move. [1]

These are described patterns, not rules that define every individual. A healthcare professional can explain anatomy in an individualized and respectful way.

What conditions can affect the pelvis?

The bones and joints of the pelvis can have the same broad types of injuries that affect other parts of the body, including fractures, dislocations and repetitive strain injuries. Pelvic joints can also develop arthritis. Pregnancy and childbirth can cause temporary pelvic-joint pain. [1]

Category	Conditions named
Bone and joint conditions	Cephalopelvic disproportion, pelvic fractures, sacroiliitis, spondyloarthritis and symphysis pubis dysfunction.
Tailbone-related condition	Coccydynia.
Connective-tissue-related conditions	Ischial bursitis, pelvic congestion syndrome, piriformis syndrome, pudendal neuralgia and round-ligament pain.
Other broad problems	Dislocations, repetitive strain injuries, arthritis and temporary pelvic-joint pain associated with pregnancy or childbirth.

This list is educational, not a diagnosis. Pelvic pain can involve bones, joints, connective tissues or organs in the pelvic region, so persistent or concerning symptoms should be discussed with a healthcare professional.

How is pelvic health checked?

Three types of exams or tests can check the health of the pelvis: a pelvic physical exam, pelvic ultrasound and pelvis X-ray. The appropriate evaluation depends on the symptoms and the clinician’s assessment. [1]

Evaluation	What it is
Pelvic physical exam	An exam of the pelvis.
Pelvic ultrasound	A test that can check the pelvis.
Pelvis X-ray	A test that can check the pelvis.

Do not assume that one test is appropriate for every symptom. A qualified healthcare professional can explain what an evaluation is intended to assess.

An overview of pelvic evaluation and care navigation.

How does the pelvis change during pregnancy and childbirth?

The pelvic opening serves as the birth canal during vaginal delivery. During pregnancy, pelvic joints relax and prepare to expand for childbirth, which can cause discomfort. [1]

People may worry about pelvic shape and delivery. Pelvic shapes vary widely, and all types deliver healthy babies. Pelvic shape alone should not be treated as a prediction of an individual pregnancy or delivery outcome.

When should pelvic symptoms be assessed?

Pelvic symptoms should be assessed by a qualified professional if they persist, interfere with daily activities, follow an injury or cause concern. Because pelvic pain may involve bones, joints, connective tissues or organs, contact a qualified healthcare professional if symptoms persist, interfere with daily activities, follow an injury or cause concern.

Conclusion: the pelvis is a support structure and a region of the body

The pelvis is both a bony structure and, in everyday clinical language, a broader body region. Its bones and joints support the upper body, connect the trunk to the legs and help the body sit, stand and walk. Its cavity holds urinary and reproductive organs, and its central opening serves as the birth canal during vaginal delivery.

Pelvic anatomy includes five bones, several important joints and a wide spectrum of shapes. Pelvic conditions range from fractures and arthritis to connective-tissue problems and temporary pregnancy-related joint pain. A pelvic physical exam, ultrasound or X-ray may be used as part of an evaluation.

Use this guide to prepare questions for a qualified healthcare professional. Clear anatomy information is a starting point for better care—not a diagnosis.

Frequently Asked Questions

What is the pelvis?

The pelvis is a bony structure inside the hips, buttocks and pubic region. It forms a basin at the base of the spine, supports the trunk and connects the upper body with the legs.

How many bones make up the bony pelvis?

Five separate bones combine to form it: the sacrum, coccyx, ilium, ischium and pubis.

What are the “sit bones”?

The ischia, or paired ischium bones, are the U-shaped bones that form the bony part of the buttocks.

What is the pubic symphysis?

The pubic symphysis is the joint where the two pubic bones meet at the front and center of the pelvis.

What are the sacroiliac joints?

The sacroiliac joints are the joints that connect each ilium bone to the sacrum.

What is the acetabulum?

The acetabulum is the hip socket, formed where the ilium, ischium and pubis meet, where the thigh bone connects to form the hip joint.

Does everyone have one of four pelvis shapes?

No. Four traditional shape categories—android, anthropoid, gynecoid and platypelloid—are still used as reference points, but current understanding recognizes pelvic shapes as a spectrum.

Can pelvic shape affect childbirth?

The pelvic opening serves as the birth canal during vaginal delivery. Pelvic shapes vary widely, and all types deliver healthy babies. Individual pregnancy and delivery questions should be discussed with a qualified healthcare professional.

What conditions can affect the pelvis?

Examples include fractures, dislocations, repetitive strain injuries, arthritis, sacroiliitis, spondyloarthritis, coccydynia and symphysis pubis dysfunction. Other pelvic-region conditions include ischial bursitis, pelvic congestion syndrome, piriformis syndrome, pudendal neuralgia and round-ligament pain.

What tests can check the pelvis?

A pelvic physical exam, pelvic ultrasound and pelvis X-ray.

Can pregnancy cause pelvic pain?

Yes. Pregnancy and childbirth can cause temporary pelvic-joint pain, and pelvic joints relax and prepare to expand during pregnancy.

Related Reading

Pelvis X-Ray: What It Shows, What to Expect and When You Need More Imaging explains the X-ray of the pelvic bones used for fractures and arthritis.

References

1. Cleveland Clinic. Pelvis: What It Is, Where It Is, Types & Anatomy. Cleveland Clinic. Updated September 24, 2024. https://my.clevelandclinic.org/health/body/pelvis

2. Betti L. Shaping birth: variation in the birth canal and the importance of inclusive obstetric care. Philos Trans R Soc Lond B Biol Sci. 2021;376(1827):20200024. PMID 33938285. https://doi.org/10.1098/rstb.2020.0024

3. Carter C, Guerra S, Clothier L, et al. Rehabilitation after pelvic fragility fracture in older adults: a scoping review. Osteoporos Int. 2025;36(7):1143-1154. PMID 40522395. https://doi.org/10.1007/s00198-025-07552-8

Disclaimer

This article is for general educational purposes and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified healthcare professional with any questions about a medical condition or treatment.