Ischium
Original Editor - Lucinda hampton
Top Contributors - Lucinda hampton
Introduction[edit | edit source]
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:
- Body of the ischium - the portion that forms the posterior one-third of the acetabulum.
- Ramus of the ischium[1].
Ramus of Ischium[edit | edit source]
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:
- Ischial tuberosity - a bony process on the ramus of the ischium at the lower end of the lesser sciatic notch.
- Ischial spine - a bony prominence found on the ramus of the ischium between the greater and lesser sciatic notches.
- Lesser sciatic notch - a notch on the ramus between the ischial spine and the ischial tuberosity.
- Greater sciatic notch - a larger notch located between the posterior inferior iliac spine and the ischial spine[1].
Ischial Tuberosity[edit | edit source]
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
Muscle Origins from the Ischium[edit | edit source]
- superior gemellus from the ischial spine
- inferior gemellus from the upper border of ischial tuberosity
- semimembranosus from the superolateral impression of ischial tuberosity
- biceps femoris long head and semitendinosus from the inferomedial impression of ischial tuberosity
- quadratus femoris originates between the origins of inferior gemellus and adductor magnus
- adductor magnus starts from the ischiopubic ramus and the inferolateral aspect of the ischial tuberosity
- gracilis muscle (a smaller part) originates from the inferior part of ramus and adjoining conjoined ischiopubic ramus
- deep and superficial transverse perineal muscles originate from the body of ischium
- obturator internus and obturator externus muscles have part origins from the superior part of the ramus
- piriformis muscle arises from the superior aspect of the greater sciatic notch[3].
Ligamentous Attachments[edit | edit source]
- 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]
Include:
- The ischium is associated with hip osteoarthritis, a common ailment characterized by erosion of necessary cartilage and wear and tear of the hip joint.
- Ischial Tuberosity bursitis
- 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]
- ↑ 1.0 1.1 1.2 Anatomy net Ischium Available:https://anatomy.net/ischium (accessed 6.11.2021)
- ↑ Health Line Everything You Need to Know About Your Ischial Tuberosity Available: https://www.healthline.com/health/ischial-tuberosity (accessed 6.11.2021)
- ↑ 3.0 3.1 Radiopedia Ischium Available: https://radiopaedia.org/articles/ischium?lang=gb(accessed 6.11.2021)