Anatomy Moment: A Trip Around the Hip

As we get into the summer months, I thought, what better time to write about the hip?  Just kidding -there’s no seasonal reason for my post, but I am inspired to spend some time breaking down the anatomy of the hip and pelvis, as I find in my classes and sessions that is it an often misunderstood (or not-well-understood) area.  As you know if you’ve been reading these posts for awhile, we are anatomy nerds here at Corpo Kinetic, and we love sharing.  Here we go!

What exactly is the hip?  In everyday language, it tends to reference a very broad area of the body including the boney points in the front where we would rest a belt, the musculature on the sides of the pelvis, and occasionally the glutes (butt muscles) as well.  Somewhere in that broad structure of bones and muscle we know there’s a joint called the hip socket or hip joint.  Are the muscles on the insides of our legs part of the hip?  What about the boney structure slightly above the glutes, in the center?  Is that low back or hip?

The general amorphous quality of the word “hip” explains why, if someone comes into our studio complaining of hip pain, our first question will likely be, “where in the hip?”  Outside of the Pilates studio, there may be no need to be so specific, but inside the studio, knowing specifically what part of your anatomy is bothering you can help us to better treat the cause of your discomfort.  When my anatomy brain starts to break down and explain the colloquial term “hip,” the first thing I go to is:

It’s actually many parts.

Look at that!  Look at how many labels there are!  And those are just the bones!  Those labels are just some of the many smaller parts which make up what we think of as the “hip.”  Labels and names are a fun thing to think about if you’re an anatomy nerd.  However, whether you’re ready to dive deep into learning anatomy or not, some basic knowledge about the function of our hip is useful in understanding why we have all those labeled parts.  When I think function of the hip, two things come to mind:

  • The hip is responsible for transferring the load of the upper body to the lower body.  (And that load includes the weight of the upper body as well as everything the upper body is carrying, from grocery bags to backpacks.)
  • Fluid mobility of the hip is crucial for keeping stress out of our knees, feet, and lower back as we bend, get up from sitting, go down stairs, and more.

Pilates works on creating stability in parts which are too mobile and mobility in parts which are too sticky.  When we look at core function, hip musculature which is not mobile enough can decrease the ability of your core to fire correctly.  On the flip side, hips which are too mobile can transfer unwanted movement up into the lower back, potentially causing pain and injury.  It’s all about balance, and luckily that’s something we thrive at in Pilates – creating balanced support for the body.

Let’s get down to business.  Here is our picture from before, a side view of the right hip.

If we were to have this person take a quarter turn and face us, we would see something like this, a picture of the right and left hips, connected by the pelvis:

Let’s break it down!  My first matter of business is a small clarification from the perspective of anatomical language.  “Hip” is a vague term, as discussed above, so for clarity I prefer to talk about the “hip sockets and pelvis.”  Remember all that other stuff from my initial question, “What is the hip?”  We had:

  1. boney points in the front where we would rest a belt
  2. the musculature on the sides of the pelvis
  3. the glutes (butt muscles)
  4. a joint called the hip socket or hip joint
  5. the muscles on the insides of our legs
  6. the boney structure slightly above the glutes, in the center

Number 4 from above is the hip socket.  The rest of the bones listed above (1 & 6), are part of the pelvis.  Numbers 2, 3 and 5 I would call muscles which move the hip socket.  Are all of these part of the hip?  Yes because that’s how we tend to talk about it in everyday language, and no because the hip socket is actually a very small component of the area we tend to refer to when we say hip, and the rest of our boney structure is the pelvis.

Starting with the pelvis, if you were to sassily put your hands on your hips, they would most likely land on a ridge of bone which wraps around the sides of your body, including the back and the front.  That ridge is part of one of the most easily felt bones of the pelvis called the ilium (actually, you have two, a right and left ilium).  Your hands are resting on a part of the bone called the iliac crest.  It’s easily felt because it’s not densely covered in muscle, as is the majority of the rest of the ilium.  The ilium bones serve several important functions, including housing and protecting our pelvic organs (those are important!), and providing large surface areas for muscles which move the hip socket to attach.

If you follow that ridge to the front and down a couple inches or so from the top, you’ll find a more pointy part which sticks out to the front.  This point is called the “anterior superior iliac spine.”  (Got that?  Anatomists often call it ASIS for short, so let’s follow their lead.)

The parts of bones which are easily felt and sort of “stick out” are often referred to as “boney landmarks” because they give us information on the placement of things we can’t as easily feel or see beneath the surface.  The ASISs are an important boney landmark for looking at the levelness of your pelvis.  Your Pilates instructor might check the levelness of your right and left ASISs to determine if your pelvis is level side to side.  We can also use the ASIS with other boney landmarks to determine if your pelvis is level front to back.

If you walk your hands back up to the top of your iliac crests (where you put your hands sassily on your hips earlier) and then follow the crest towards your back, they will slope down and together.  As you follow those slopes, you might feel two little dimples.  These are your sacroiliac joints, or SI joints for short.  In very close proximity to the SI joints are the posterior superior iliac spines (PSISs).  When you are standing and the PSIS and ASIS are level, then your pelvis is level front to back.

Did you have a hard time feeling the dimples or PSISs?  Don’t worry.  They are far less prominent than the ASISs.  When I was a new instructor, it took me quite some time and checking multiple different pelvises before I felt confident that I was on the right spot.  We use the PSISs as instructors because it is more precise, however a far easier way to check where your pelvis is on your own (and for everyday use precise enough) is to use a different boney landmark.

So – come back to your sassy hands on hips position.  Follow that boney ridge, your iliac crest down to your ASISs.  Keep walking your hands down and together.  We have more muscle here, so you may loose track of the iliac crest – you can use the crease in your pants where the leg meets the pelvis as a guide.  When your hands meet in the center, you’ll be on what we often refer to in the Pilates studio as the pubic bone.  If you look back at our front-facing picture above, they’ve labeled the point in the center as the “pubic symphysis.”  We actually have two pubic bones, a right and a left, which are connected by a dense and fibrous tissue called the pubic symphysis.  This connection is mostly immobile (and should be).  Fun fact, during pregnancy the body releases a hormone which relaxes all ligaments in preparation for birth, including the fibrous pubic symphysis.  This is why we modify certain leg exercises for momma’s-to-be.  Mommas need to be strong, and in most cases can work out hard, but we want to promote that strength without creating shearing at the pubic symphysis.

So – you know where your pubic bone is and where your ASISs are.  If you put the heels of your hands on your ASIS’s and your fingertips on your pubic bone, you can now line up your ASISs and your pubic bones in a vertical plane.  This is another way to tell if your pelvis is level front/back, and usually fairly easy for us to check on our own.

Let’s land on the iliac crests again (sassy hips), then take our trip back around to the PSISs and SI joints.  Walk your hands one more time down and together along the iliac crests and eventually land on those dimples.  Remember that the name of those dimples is the Sacro-Iliac Joint.  Iliac stands from the ilium part of the joint, which we’ve already visited.  Sacro stands for the sacrum, which is the broad flat part in the center back of your pelvis.  Here’s a view of the pelvis and hip joints from the back, as if the person were facing away from us.

It provides a good view of the slope down from the iliac crest (sassy hips!) to the sacroiliac joints, and the sacrum nestled in between the right and left iliums.   At the base of the sacrum lies the tail bone, or coccyx.  There is actually also a joint between the sacrum and coccyx, and the tailbone can move, occasionally being displaced.  The name of this joint is kind of fun:  sacrococcygeal.

At this point, we’ve visited three joints of the hips and pelvis which we often don’t think of as joints: the pubic symphysis (front, down, and center), the sacroiliac joint (on the back, the dimples at the top of the sacrum), and the sacrococcygeal joint (between the sacrum and tailbone).  These three are joints because they do move, but key to their health is that they actually don’t move very much.  Most of the movement in our hips and pelvis should come from the true hip joint – where the thigh bone meets the pelvis.  This joint is a classic “ball in socket” joint, and it’s mobility allows us to squat to the floor, climb mountains, ride horses, and much more.  This is the joint that we want to keep mobile, in all planes of motion, so that our smaller, less mobile joints are not overly stressed.

Phew!  I hope you’ve enjoyed this trip around the hip.  Now take your newfound knowledge and move it!  If you’re not coming to the Pilates studio today, taking a walk up some serious hills is a great way to get mobility and strength in your hips.  See you soon!