The pelvic girdle or the bony pelvis is a bony ring, formed by the left and right hip bones and the sacrum, and it surrounds the pelvic cavity, and connects the vertebral column to the lower limbs.

The main functions of the pelvic girdle are to transfer the weight of the upper body to the lower limbs when sitting or standing, and provide attachment points for muscles that help with locomotion and posture.

It also provides support and protection for the abdominopelvic structures. So let’s start with the hip bones.

The right and left hip bones are irregular shaped bones located at the sides of the pelvic cavity, which bound and form the lateral walls of the pelvis.

Each one of these hip bones develop from the fusion of three bones, the ilium, ischium, and pubis. Now, let’s start with the upper part of the hip bone, the ilium. You can think of the ilium as a fan.

It has an upper expanded part representing the spread of the fan called the ala, and a lower narrow part representing the handle of the fan called the body.

Now, there are 4 bumps coming off the ilium called spines. Let’s talk about them!

If we look anteriorly to the ilium, we can see two of the spines. One of them is superior and the other one is inferior. The naming is easy because it follows the rule of (Anterior or Posterior) + (Superior or Inferior).

The superior one is called the anterior superior iliac spine, and the inferior one is called, you guessed it, the anterior inferior iliac spine.

Now, looking at the ilium from a posterior view, we can see the remaining two spines, one superior and again, one inferior. If we follow the rule just mentioned, we can name them easily.

The superior one is called the posterior superior iliac spine, and the inferior one is called, wait for it, posterior inferior iliac spine.