What Is a Coxal Bone?

The sacrum and the coxal bone combine to form the pelvis.
A coxal bone is also known as a hipbone or innominate bone.
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  • Written By: Heather Phillips
  • Edited By: Michelle Arevalo
  • Last Modified Date: 11 September 2014
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A coxal bone is also known as a hipbone or innominate bone. The Latin name for the coxal bones is ossa coxae. The two coxal bones make the receiving sockets of the hip and leg joints, creating a cup-like space called the acetabulum. This space receives the ball end of the femur, which is the main upper bone in the leg.

The coxal bone is actually three separate bones that fuse together as a person grows from childhood into adulthood. These three pieces are called the ilium, ishium, and pubis. They all typically fuse, or join, into one larger bone by the time a person reaches between 20 and 25 years of age.

The ilium forms the upper element of the coxal bone, with a crest-like structure at the uppermost part. A person putting his or her hands on his or her hips can actually feel the crest part of the ilium. The ishium is the back part of the acetabulum, and is one of the bones a person sits on. The pubis is located in the front, and forms the frontal part of the acetabulum opening, as well as offering protective coverage to the organs in the pubic area.


The shape of the coxal bone is irregular and flattened. It is wider at the top and bottom than in the center. It supports the upper body’s weight and prvides structural integrity of the vertebral, or spinal, column. In addition to offering support to the upper body, another primary function of the coxal bones is the protection and support of the bladder and reproductive organs.

Along with the sacrum and coccyx, the coxal bones make up the structure called the pelvic girdle, or pelvis, and form the pelvic cavity. On each side of the human body a coxal bone joins the sacrum in the back. In the front, a muscle known as the pubic synthesis joins the coxal bones.

The shape of these bones differs between men and women. This is primarily because of the role they play in human reproduction. Male coxal bones are bigger and closer together. Females have more delicate coxal bones that are also more widely spaced.

In a pregnant woman, the coxal bones are also responsible for supporting the fetus inside the uterus. The bones have the ability to loosen a bit as the pregnancy progresses. This allows for the delivery of the baby at the end of the pregnancy.


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Post 3

My sister experienced pelvic girdle pain while pregnant with her daughter. She said it hurt to turn over in bed, to walk, and especially to climb stairs.

Her doctor told her that the pain was caused by one pelvic joint becoming stiff. This irritates the other joints. He told her if she got treatment for the stiff joint, then all the joints should start moving normally once more, and the pain would go away.

We rarely think about our coxal bones until they cause us pain. My sister was surprised to learn that there were several pelvic joints, but she’s glad that the treatment was so simple.

Post 2

@cloudel - Ouch! That must have been incredibly painful for her. I can’t imagine breaking the bone that attaches the lower body to the upper body! She must have felt very disconnected.

I don’t know how you could even sit down if you crushed that bone. She must have had to lie flat for months!

I bruised the area around the left side of my coxal bone badly, and I couldn’t walk right just from that. It took about a week before I could walk regularly. I am glad that your cousin is recovering! It’s nice to know that it is possible to get back to life after such an event.

Post 1

The coxal bone would be a very bad bone to break. My younger cousin broke hers in an automobile accident, and her doctor told her she would probably never walk again.

The wreck was so bad that she was unconscious for a couple of days afterward. While she was out, the doctor x-rayed her entire body to check for broken bones. He saw that her coxal bone had been crushed.

Two years later, she has proven the doctor wrong. She is walking with the aid of a special crutch. She is going back to college, which she was in at the time of the wreck. She has had to wait quite awhile to get her life going again.

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