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Introduction[edit | edit source]

Ischium posterior view.png

The ischium (Latin: os ischii) is a paired bone of the pelvis that forms the lower and back part of the hip bone, as well as the posterior and inferior boundary of the obturator foramen.

Image 1: Ischium posterior view, Image 2: anterior view

The ischium consists of two main parts:

  1. Body of the ischium - the portion that forms the posterior one-third of the acetabulum.
  2. Ramus of the ischium[1].

Ramus of Ischium[edit | edit source]

Ischium anterior view.png

The ramus of the ischium is the part of the bone that extends downwards from the body, then turns anteriorly and unites with the inferior ramus of the pubic bone. The ramus of the ischium presents the following landmarks:

  1. Ischial tuberosity - a bony process on the ramus of the ischium at the lower end of the lesser sciatic notch.
  2. Ischial spine - a bony prominence found on the ramus of the ischium between the greater and lesser sciatic notches.
  3. Lesser sciatic notch - a notch on the ramus between the ischial spine and the ischial tuberosity.
  4. Greater sciatic notch - a larger notch located between the posterior inferior iliac spine and the ischial spine[1].

Ischial Tuberosity[edit | edit source]

Ischial tuberosity lateral view.png

The ischial tuberosity (sit bone) is divided transversely into upper and lower areas, upper subdivided by an oblique bony ridge separating the various muscle attachments.

Image 3: lateral view of Ischial Tuberosity

  • Three tendons connect the hamstring to the ischial tuberosity.
  • The gluteus maximus muscle covers the ischial tuberosity when your leg is straight and your thigh is extended. When your knee is bent and your thigh is flexed, the gluteus maximus moves and leaves the ischial tuberosity uncovered, exposing the ischial tuberosity when you sit down.[2]
  • Prolonged pressure on the ischial tuberosity can lead to Ischial Bursitis

Image 4: Bony Landmarks of the pelvis

Pelvis landmarks.jpeg

Muscle Origins from the Ischium[edit | edit source]

Ligamentous Attachments[edit | edit source]

  • Pelvis anatomy.jpg
    sacrospinous ligament attaches to the ischial spine
  • sacrotuberous ligament attaches to the posterior iliac spine and medial ischial tuberosity and part of it extends as the falciform ligament along the inferior ramus of ischium
  • ischiofemoral ligament which forms the capsular reinforcement of hip joint[3].

Associated Conditions[edit | edit source]



  1. The ischium is associated with hip osteoarthritis, a common ailment characterized by erosion of necessary cartilage and wear and tear of the hip joint.
  2. Ischial Tuberosity bursitis
  3. Fracture or injury to the pelvis, including the ischium, can vary greatly in severity, with surgery sometimes being necessary to correct the problem.[1]

Image 6: Acetabulum of hip

References[edit | edit source]

  1. 1.0 1.1 1.2 Anatomy net Ischium Available: (accessed 6.11.2021)
  2. Health Line Everything You Need to Know About Your Ischial Tuberosity Available: (accessed 6.11.2021)
  3. 3.0 3.1 Radiopedia Ischium Available: 6.11.2021)