The ischium (Os ischii) is a flat bone of the human pelvis. It borders the pubic bone (Pubis) and the iliac bone (Os ilium) and together with these forms the so-called hip bone (Os coxae). This closes the complete pelvic ring with the sacrum and thus forms the basis of the bony pelvis.


The structure of the ischium can be divided into 3 parts, the ischial body and an upper and lower ischial branch, which merge into one another. The Body of the ischium forms the largest part the acetabulum and its posterior limitation. It has two characteristic notches on its back (Incisura ischiadica major / minor). The larger of the two ends in a sharp bone spine, which serves as the starting point for the sacrum-ischial spine ligament (Sacrospinal ligament) acts. This is part of the Sacrum-iliac joint and contributes to its stabilization. Together with another band, it also forms the boundary of the small ischial hole at the small notch, which is an important one Entry point for ducts from the pelvis to the thigh and groin region.

Together with the upper branch of the pubic bone, the upper ischial branch (Ramus superior ossis ischii) the overhead limitation of the hip hole (Obturate foramen), through which several ducts run from the pelvis to the leg.

A prominent bone edge delimits the outside of the branch from the back and serves as the point of origin of various thigh muscles. The inside is part of the bony wall of the small pelvis and also has a sharp edge in its lower part. This forms the starting point for another tether of the sacrum-iliac joint. It also serves as the point of origin for part of the pelvic floor muscles.

The lower ischial branch knows on its outside an uneven surface from which the Obturator muscle externus arises. The inside is part of the bony front wall of the small pelvis and, with its bone edges, forms the starting point for connective tissue parts of the pelvic floor.

On of their At the back, the two ischial branches run together into the large ischial tuberosity (Sciatic tuberosity) out.

Sciatic tuberosity

The ischial tuberosity is a prominent bone protrusion, which forms the lower end of the bony pelvis. It has a rough surface and essentially fulfills two functions.

On the one hand, he makes that Origin point for a whole group of Muscles of the thigh and gluteus muscles, the so-called thigh flexors. These pull from there over the back of the thigh to below the knee, where they attach to the lower leg bone. Above all, they serve to flex the knee joint and stretch the hips, which is crucial, for example, in movements such as climbing stairs.

On the other hand, the ischial tuberosity serves as a Support point when sitting and is superimposed on this by an extensive pad of fat.


Due to its anatomical location, the ischium has three main functions.

On the one hand, as the name suggests, it serves with its large ischial tuberosity as the lowest point of the bony pelvis and thus for the Support point when sitting.

On the other hand, with its numerous bone edges and tips, it functions as a Point of origin of several muscles of the thigh and the pelvic floor.

However, its main role is mainly to Stabilization of the bony pelvic ring. It fulfills this on the one hand through its firm connection with the pubic and iliac bone, on the other hand through its function as the starting point of several ligaments of the sacrum-iliac joint. These are stretched very tightly between the bones and thus provide the necessary stability in the pelvis.

Pain in the ischium

Pain in the ischium can have a variety of causes. These can best be classified according to the group of structures that are affected.

On the one hand, processes on the bone itself can be the cause of the pain. The main causes here are fractures caused by falls or accidents, inflammation of the bone tissue and tumors. In adolescents, jerky leg movements or excessive strain, e.g. through hurdles, as well as long and high jumps, can also lead to so-called Apophysiolysis come. These are tears in the ossification centers, which play a crucial role in bone growth.

Another reason for pain in the ischium area can be injuries to the connective or muscle tissue. These are mainly bruises, e.g. from falls, as well as strains and muscle fiber tears from overuse. There is also frequent irritation and inflammation of the muscle tendons on the ischial tuberosity due to friction between the tendons and the bones. Inflammation of the muscles themselves is less common.

The os ischii and its adjacent structures form several passageways for nerves that run from the pelvis to the leg. These can also cause irritation and, in particular, entrapment, which can cause severe pain as a result.

Also read on this topic: Ischial tuberosity pain

Inflammation of the ischium

In principle, inflammation can develop in any of the structures on the ischium. Inflammation of the bones is rather rare. They usually arise as a result of other inflammations in the area, e.g. inflammation of the bladder, which then spreads to the ischium. Essential inflammation of the muscles or especially their tendons of origin. These usually arise as a result of excessive strain on the muscles due to excessive training or an unfamiliar load. Furthermore it can be too Inflammation of the so-called Bursa come. These are structures that mainly occur on joints. They are filled with liquid and serve to dampen pressure and thus relieve the joints. Bursitis is also often caused by excessive stress, but also by bacterial infections, arthritis, osteoarthritis, gout, tuberculosis or gonorrhea.

Irrespective of its location, inflammations are usually expressed in the so-called cardinal symptoms: Swelling, redness, overheating, pain and impaired function the affected structure.

They are usually treated with nonsteroidal anti-inflammatory drugssuch as Ibuprofen® or Voltaren®, as well as immobilization and cooling. Painkillers can also be given, depending on the severity of the pain. In addition, physiotherapeutic exercises are recommended, which primarily serve to strengthen the trunk and pelvic floor muscles, as well as to stretch the thigh muscles attached to the ischium. This is to prevent future inflammation and injury from overuse.

Ischial fracture

Fractures of the ischium go mostly with injuries to the pubic bone and are also called anterior pelvic ring fractures designated. They can exist as stable or unstable fractures.

As stable are fractures that are either unilateral or bilateral but without shifting the break lines. Unstable Accordingly, fractures are accompanied by a shift in the break lines.

Since the entire pelvic ring is a very robust and strong bony structure, fractures are in this area almost always the result of massive violence, e.g. due to accidents or serious falls. It manifests itself in very severe pain and the loss of mobility of the leg on the affected side.

An X-ray or CT scan will be taken to confirm the fracture. The therapy usually consists of 1-2 days of strict bed rest and subsequent stress, as is possible in the context of pain. If necessary, a belt or bandage is used to stabilize the pelvis. Painkillers and drugs are used to prevent inflammation. Surgical intervention may be necessary depending on the type and severity of the fracture. This is the case, for example, if the break lines have to be straightened again or damage to neighboring organs, e.g. the kidneys or the urinary tract, the liver, spleen, the intestine or nerves running in the pelvis has occurred.

With adequate treatment, the fractures usually heal without permanent damage.