Osteology of the Pelvic Girdle: An Overview

Today I decided to write about the bones that make up the pelvis. This is one of the first things I learnt this year, so it is probably time to go over them again before I forget. I won’t go into detail about the different articulations as that will not help you or me. Ideally, it is best to learn the specifics whilst handling a model or using an app that visualises anatomy in 3D. However, I will aim to provide a basic overview.

Function of the strong and stable pelvis

  • To provide structural support for the vertebral column, as well as aid movement
  • To protect lower abdominal organs
    • True and false pelves protect different organs, check my diagram below for further information.
  • To provide attachment for various muscles and tendons
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False vs true pelvis [Larger image]

The basics

Pelvic girdle contains two hip bones (each has three parts: ischium, ilium and pubis), sacrum and coccyx. Hip bones join anteriorly via the pubic symphysis (hyaline cartilage). Bilateral posterior attachment of the hip bones to the sacrum is through sacroiliac joints. There is also a sacrococcygeal symphysis between the sacrum and the coccyx.

What makes a hip bone?

  • Ilium (Latin meaning: flank) – largest component, most superior.
  • Ischium (Latin meaning: hip joint) – the posterior and inferior part of the pelvic bone.
  • Pubis (Latin meaning: groin) – the anterior and inferior part of the pelvic bone. Contains a body and two rami (arms)

Acetabulum (Latin meaning: vinegar cup – how cute) – the point where ilium, ischium and pubis meet and produce a socket for the head of the femur (forming the hip joint).

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Pelvis from the side [Larger image]

Male vs Female pelvis

Bones in males (compared to females of same age) are generally larger and posses a larger surface area. Pelvic girdle is not an exception. Most differences between the sexes are due to adaptations for pregnancy and childbirth.

Women naturally have a wider, shallower pelvis. This means that there is more space in the pelvic inlet and outlet, making the passage of the foetal head during childbirth possible.

Other differences:

  • Females
    • inlet is circular
    • pubic arch is around 80-85 degrees
    • ischial spines project less into the pelvic cavity
  • Males
    • inlet is heart shaped
    • pubic arch is around 50-60 degrees
    • ischial spines project more into the pelvic cavity.

There are many others and I would strongly suggest that you would go and check them out. Most anatomy textbooks should have a section related to this (Principles of Anatomy & Physiology by Tortora and Derrickson has a very detailed table).

Many articulations, many names

Anatomy becomes so much easier to learn when you know the meanings behind the latin names. Here are a few examples (definitions in bold):

  • Obturator foramen – opening, hole
  • Ischial tuberosity – big protrusion for muscle/ligament attachment
  • Pubic tuberclesmall protrusion for muscle/ligament attachment
  • Anterior superior iliac spinepointy protrusion for muscle/ligament attachment

Until next time!

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Pelvic girdle [Larger image]

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