Anatomy and Physiology

Anatomy is the study of the different bits of the body, and physiology is the study of how those bits work.

It is tough to add any unique or new information about the human body, since so much is already known. Still, a new ligament was found in the knee in 2013. So anatomy is more or less fixed information, and there are many excellent books and websites devoted to those things.  I most strongly recommend Blandine Callais-Germaine’s Anatomy of Movement and Andrew Biel’s excellent book Trail Guide to the Human Body. Both understand that anatomy is about movement, and that knowledge is about interacting with the environment: touching, exploring, moving.

Still our understanding of how the bits of the body work is evolving. We are developing new ways of assessing function, and rethinking old ideas. This is a great place to ask those questions, and learn about those things.

A question so hip, it gets to start the discussion:

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Hi Blake,
Would you refer to the hip bone or os coxae as the ilium bone? In this book that I am reading “Preparing for a Gentle Birth” by Blandaine Calais-Germain and Nuria Vives Pares – that is what she calls it and I thought it was the ilium a the top…. I get that there are different names and I guess I just want the most common for the students taking our MamaNurture 100-hour prenatal yoga teacher training.

Also can you let me know if the below statement is the best way to really simplify the pelvis? Is it correct?

“The pelvis is made up of four bones arranged in a ring. These bones are the left and right os coxae (hip bones), the sacrum (five fused vertebrae at the bottom of the spine) and the coccyx (tailbone). The hip bones or os coxa are comprised of three fused bones: the ilium, ishium and the pubis.”

Shannon Crow


Hi Shannon:

 So here is a way to look at it. The ‘hip’ is an indistinct region.  It is kind of like referring to ‘the west’ when talking about nations that are not Europe, Africa or Asia. You could say ‘the west country’, but that would be kind of strange. Saying ‘the hip bone’ is the same. It is a very non-specific nomenclature, and is not useful for any meaningful anatomical discussion.
The ‘pelvis’ is more distinct, but still largely a region. It is like saying ‘North America’ It denotes a discrete and definable region. But of course, you would not say ‘the country of North America’. You might say ‘the countries of North America’. So, you could say ‘the bones of the pelvis’, but you wouldn’t say ‘the pelvis bone’. As a group of bones, the pelvis has a unique structure and function, making a ring that distributes forces from the legs up through the spine, and also supporting the viscera and allowing for attachment of various muscles and structures for powerful movements of the legs. The ring of the pelvis allows for the continuation of the alimentary canal for waste elimination, but in females also provides an opening for sexual fertilization of a zygote, and the subsequent parturition of the fetus.
Each of the bones: the ilia (ilium, singular) the ischia (ischium, singular) pubes (pubis, singular) sacrum (5 vertebrae) and coccyx, are like the individual countries, like Canada, the United States, Mexico, Barbuda, Cuba, Guatemala, Jamaica and other nations. The ‘os coxae’ (os coxa, singular) are the specific united bones of the ischium, ilium and pubis. The sacrum and coccyx are NOT part of the os coxae, in the same way that Barbuda, Cuba and Jamaica are NOT continental countries.
So in direct response to your question, I would say the ilium is a part of the os coxa, which is part of the pelvis, which people sometimes refer to as ‘the hip’. I would say this in same way I would say Canada is part of continental North America, which some people refer to as ‘the west’. The ilium is the broad top part of the os coxae, closest to the ribs. I would argue there is no such thing as ‘the hip bone’.
I don’t like equating the ‘hip bone’ and the ‘os coxae’. I just do not like the term ‘hip’, because people mean so many things when they say it. Some people actually mean the greater trochanter of the femur when they say ‘hip bone’.  I try to teach my students to refer to very specific bones and structures.  I might say ‘hip joint’ to refer to the coxo-femoral joint, but it is generally understood: people typically do not refer to the sacro-iliac joint as ‘the hip joint’. When I teach my students, I typically will give them the term I would like them to use, and then I just let them know that other authors will refer to it as ‘x’ or ‘y’. So while your quoted paragraph is not ‘wrong’ it is not as right as possible. You could say what she says, but personally I never would.
Most people say ‘pelvis’ which I think is pretty clear, so long as you define which bones are part of it.  In that way, I like that term best.  I usually say ‘the bones of the pelvis are the united bones of the ilium, ischium and pubis on the left and right sides, as well as the sacrum and coccyx. The ilium, ischium and pubis are already fused in the fetus’. I might then say ‘many authors refer to the fused bones of the ilium, ischium and  pubis as the os coxae‘. Some authors define the pelvis as ONLY the bones of the os coxae, while others define the pelvis as the os coxae AND the sacrum.
Personally, I rarely talk about the os coxae: I refer to ilia, ischia, pubic bones and sacrum and coccyx specifically, since I like to help people become familiar with the respective structures.
Hip:Region>Pelvis:Structural group of bones in hip region>os coxa: unified bone in pelvis, but NOT the sacrum> ilium: superior portion of os coxa.
I hope that is clear and helpful.

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