Ischium

The ischium (/ˈɪski.əm/; pl.: ischia) is a paired bone that forms the lower and back part of the hip bone. It is an important part of the body that 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 come together to make the coxal bone.

The top part of the ischium helps create about one-third of the acetabulum, which is a deep socket in the hip that allows our legs to move smoothly. This makes the ischium essential for our ability to walk, sit, and stand.

Structure

The ischium is made up of three parts: the body, the superior ramus, and the inferior ramus. The body has a spine where certain muscles begin, 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 projects downward and backward and has surfaces 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 happens when a person makes sudden movements, like sprinting or kicking a ball. The break occurs where muscles are connected to the bone.

Another condition is called ischial bursitis, which 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 was first used in English medical writing around the year 1640. It comes from the Greek word iskhion, which means "hip joint." A famous ancient doctor named Galen was the first to separate the hip area into ischium and ilium, though 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, which includes the ischium bone. In most dinosaurs, the ischium bone stretches 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 where the ischium, ilium, and pubis bones meet. This socket holds the top part of the leg bone. The way the acetabulum is positioned helped dinosaurs stand upright with their legs right under their bodies.