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Pelvic Girdle: Ilium

Time To Read

3–5 minutes

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When you put your hands on your hips to show someone disdain, you are putting your hands on this bone.  The ilium, ischium, and pubis are all fused together to form the coxal bones.

  • Iliac crest
  • Iliac fossa
  • Anterior superior iliac spine
  • Posterior superior iliac spine
  • Anterior inferior iliac spine
  • Posterior inferior iliac spine
  • Greater sciatic notch
  • Acetabulum
Hip Bone Study Sheet

Put your hands on your hips.  What you are feeling is the iliac crest.  This is the superior part of the ilium bone.  You have lots of difficult to stretch muscles like the pisiform that runs over this area. The area below this, which is a curved area is called the iliac fossa.

The big depression in the hip bone is what you might want to call the hip socket. However, it has a more complicated name: acetabulum.  This word means vinegar cup.  The acetabulum reveals that the hip bone is actually three different bones. These are the illium, ischium, and the pubis, or the pubic bone, which are fused together.  These three bones come together at the acetabulum, giving it its strength. 

When you’re presented with just a hip bone, it’s easy to find the acetabulum or the obturator foramen.  But, it’s really easy to get mixed up and not be able to tell anterior from posterior.  There’s a trick to this.  Do you know someone with back pain?  Whenever they have back pain, they mention a big nerve. This nerve runs from the back and down the leg. They might say: My sciatica is acting up.  Yes!  The sciatic nerve runs down the posterior of your legs. There are notches in the hip bone to allow its passage.  There are two notches. The greater sciatic notch is in the ilium. The lesser sciatic notch is in the ischium.  I use the greater sciatic notch to tell which is the posterior side of the bone.  See how it is this big indentation where a nerve could run. Notice how there isn’t an indentation as deep as this on the anterior side of the bone. 

There are four other structures on the ilium. These can be troublesome. This issue arises especially if you don’t know which is anterior and which is posterior. But we know to look for the sciatic notch to help us with identifying posterior.   Look at what are labeled as spines.  To me, these are like slight bumps of the outer border of the bone.  These are attachment points for ligaments and large muscles of the hips.  In fact, misalignment of these attachments that can lead to sciatic problems.  Let me just point out to you here that there are four spines.  Two are at the back, and two are at the front.  Or, you could say that two are at the top and two are at the bottom.  Each of these spines is named based on its position. It could be at the front or back, known as anterior or posterior. It could also be up or down, referred to as superior or inferior. I’m good at finding the posterior inferior iliac spine, which is sometimes abbreviated as the PIIS.  It’s right above the greater sciatic notch, which is easy for me to find.  I feel like the posterior spines are like these two nubbly fingers that come off the back of the hip. 

The anterior spines are not so easy to find sometimes. The simplicity in the naming is the same. Both are anterior, but one is superior and one is inferior.  I guess I use the iliac crest to locate the anterior superior iliac spine.  It is the very curved ending of the iliac crest at the edge of the ala.  You’re on your own with the anterior inferior iliac spine.

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FOR THE PELVIC GIRDLE
A 3D diagram of the human ilium, viewed from a lateral perspective. Key anatomical features are labeled with green lines and text: the iliac crest (the upper border of the ilium), the anterior superior iliac spine, the greater sciatic notch, the lesser sciatic notch, and the ischial tuberosity. These labels point to their respective locations on the gray scale 3D anatomical model. The position of the femur is also present, as well as a bit of the spine. The context is educational, likely showing a user the location of anatomical features.
Ilium Anatomy: 3D diagram of the ilium, with labels for the iliac crest, sciatic notch, and ischial tuberosity.
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An anterior view of a stylized pelvis, rendered in grey. The image focuses on the bony structures of the hip region and includes labels with green lines pointing to different anatomical features. Visible features include the iliac fossa, anterior inferior iliac spine, obturator foramen, and sacral foramina. Part of the head of one femur is also in view.
Anterior view of the pelvis, showing the iliac fossa, anterior inferior iliac spine, obturator foramen, and sacral foramina.
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An illustration of the human pelvis, viewed from the front, showing the bones and their anatomical relationships. Key features are labeled with green lines and text: the anterior superior iliac spine, the anterior inferior iliac spine, the pubic symphysis, and the pubic crest. The image focuses on the anterior portion of the pelvic girdle.
Anatomical view of the pelvis, highlighting the pubis, pubic crest, and pubic symphysis.
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3D gray-scale illustration of a posterior view of the hip bones. Key structures are labeled with green lines, including the posterior superior iliac spine, posterior inferior iliac spine, greater sciatic notch, and ischial tuberosity. Part of the femur is visible on the left.
Posterior view of the hip bones labeled with structures like the ischial tuberosity and the posterior superior iliac spine
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