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Ischium

Other Terms: Os ischii

Type

irregular

Description

It is an arched or U-shaped element with its concave notched margin contributing to the posterior two-thirds of the obturator foramen. It is divisible into two parts, a more posterior positioned body forming the thickest part of the os coxa and a slender anterior ramus. The superior portion of the body is the greatest contributor of the three bones of the os coxa to the acetabulum. It forms the posterior portion of the lunar articular surface for the femur and forms almost the entire rough acetabular fossa. The ischium ossifies from a primary center that appears during the fourth month in the body of the ischium. Around the seventh year the pubis and ischium join to form an ossified ramus inferior to the obturator foramen. At puberty a secondary center appears in the ischial tuberosity. This secondary center joins with the primary center anywhere between the fifteenth and twenty-fifth year.

Etymology

The term ischium has a varied and ancient origin. Hippocrates used ischion to designate both the hip joint and the hip region. More recently, Rufus used the term to mean strictly the hip socket. When Galen described this region he divided the bone into three parts and he applied the Greek name ischion to the lower part. The term eventually became the Latin term ischium.

Articulations

The ischium articulates with one bone: the femur. The ischium forms the greatest part of the bowl-like acetabulum articulates which articulates with the rounded head of the femur.

Ossification

The ischium ossifies from a primary center that appears during the fourth month in the body of the ischium. Around the seventh year the pubis and ischium join to form an ossified ramus inferior to the obturator foramen. At puberty a secondary center appears in the ischial tuberosity. This secondary center joins with the primary center anywhere between the fifteenth and twenty-fifth year.

Latin

Os ischii

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