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Ischium

Adapted from Wikipedia · Adventurer experience

Illustration showing the anatomy of human muscles and how they help us move.

The ischium (/ˈɪski.əm/; pl.: ischia) is a bone that forms the lower and back part of the hip bone. It helps us move and stand.

It sits below the ilium and behind the pubis. Together with these bones, it forms one of the three main parts that make the coxal bone.

The top part of the ischium helps create part of the acetabulum, a socket in the hip that lets our legs move smoothly. This makes the ischium important for walking, sitting, and standing.

Structure

The ischium has three parts: the body, the superior ramus, and the inferior ramus. The body has a spine where muscles start, and a bump called the ischial tuberosity that you feel when sitting, especially on hard surfaces. This area also helps muscles attach.

The superior ramus goes down and back and has places where more muscles attach. The inferior ramus is a thin part that connects to another bone called the pubis and helps form part of the pelvis. It also has areas where muscles and tissues attach.

Clinical significance

Sometimes, a part of the hip bone called the ischial tuberosity can break off during sports. This can happen when a person makes sudden movements, like sprinting or kicking a ball.

Another condition is called ischial bursitis. This happens when a small fluid-filled sac near the hip gets irritated. This often occurs from sitting on hard surfaces for long periods.

History

The word ischium started being used in English medical writing around 1640. It comes from the Greek word iskhion, meaning "hip joint." An ancient doctor named Galen was the first to separate the hip area into ischium and ilium, but he did not talk about the pubis as a separate bone.

Main article: Galen

Other animals

Dinosaurs

Dinosaurs are split into two groups, Saurischia and Ornithischia, based on their hip structure. This structure includes the ischium bone. In most dinosaurs, the ischium bone goes down from the ilium bone toward the animal's tail. The acetabulum, or "hip-socket", is a cup-shaped hole on each side of the pelvic area. Here, the ischium, ilium, and pubis bones meet. This socket holds the top part of the leg bone. The position of the acetabulum helped dinosaurs stand upright with their legs under their bodies.

Additional images

  • Right hip bone. External surface.

  • Right hip bone. Internal surface.

  • Plan of ossification of the hip bone.

  • The obturator externus.

  • Pelvis

Images

Anatomical drawing showing the structure of the male pelvis, including bones like the pubis and ischium.
Anatomical diagram showing the structure of the hip bone and attached muscles.
Anatomical diagram showing the structure of the human hip joint, including bones and ligaments.
Illustration of a human hip bone showing its internal surface and key features.
Diagram showing how the hip bone forms and grows in the human body.
Anatomical illustration showing the bones and muscles of the human pelvis and leg, from Gray's Anatomy.

This article is a child-friendly adaptation of the Wikipedia article on Ischium, available under CC BY-SA 4.0.

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