ISG - The sacroiliac joint

Synonyms in a broader sense


  • Articulatio sacroiliaca
  • Sacroiliac joint
  • Sacrum and iliac joint
  • SIG (sacroiliac joint)


  • ISG blocking
  • Scroiliitis


The ISG (medical: Articulatio sacroiliaca) is the articulated connection between the sacrum (Os sacrum) and the iliac bone (Os Ilium).
The joint surfaces (facies auricularis) between these two bones are boomerang-shaped to c-shaped and are located between the 1st and 3rd sacral vertebrae.
They consist of an upper and lower pole, the transition point of which is approximately at the level of the 2nd sacral vertebra (part of the sacrum). There is a kink between the upper and lower pole, the angle of which is 100-120 °.

Figure ISG - joint

Figure pelvis from the front: sacrum-iliac joint (red)
  1. Sacrum-iliac joint
    (Sacroiliac joint, abbreviated ISG)
    Articulatio sacroiliaca
  2. Iliac bone -
    Os ilium
  3. Sacrum -
  4. Anterior sacrum-iliac bone
    -Tape -
    Lig. Sacroiliacum anterius
  5. Fifth lumbar vertebra -
    Vertebra lumbalis V
  6. Fourth lumbar vertebra -
    Vertebra lumbalis IV
  7. Tailbone -
    Os coccyxis
  8. Pubic bone -
  9. Femoral shaft -
    Corpus femoris
  10. Lumbar cruciate ligament kink -

You can find an overview of all Dr-Gumpert images at: medical illustrations

Gender-specific differences in the articular surfaces

In women, the joint surface is much more even, so that there is much greater freedom of movement than in the ISG of the man exists.
The stabilizing factors of the joint in women are on the one hand the position of the sacrum in the pelvic ring, on the other hand the muscular and ligamentous apparatus. One speaks of the so-called Frictional connection of the joint.

The surfaces of the joint surfaces in men are characterized by numerous grooves and elevations, so that a great deal of force has to be used to achieve a displacement of the joint surfaces against each other. The result is great stability but only little mobility of the joint. One speaks of the so-called Form fit of the joint.

Stabilizing factors of the ISG

In addition to the surface properties of the joint surfaces and the position of the sacrum in the Pelvic ring A number of ligaments are responsible for the stability of the SI joint.

The most important bands are briefly described below.

  • Posterior sacroiliac ligament (ligg.sacroiliaca dorsalia)
    These are fiber strands that connect the iliac bone with the Sacrum connect.
  • Anterior sacroiliac ligaments (ligg.sacroiliaca ventralia)
    These ligament structures also connect the iliac bone with the sacrum, are rather thin and have a connection with the capsule. In their upper fiber course they form a connection with the iliolumbar ligament.
  • Ligg. sacroiliaca interossea
    These ligaments, the fiber strands of which are very dense and short, also connect with the joint capsule and fill the sacral sulcus. Due to their direct positional relationship to the capsule and by filling the sacral sulcus, they play an important role in stabilizing the SI joint.
  • Ligg. sacrospinale
    This ligament has its origin on the lower outer surface of the sacrum and the base of the coccyx, runs in front of the ligamentum sacrotuberale with which it is closely connected and starts in the area of ​​the spina ischiadica.
  • Sacrotuberous ligament
    This triangular ligament arises on the side areas of the sacrum / coccyx and iliac bone (spina iliaca posterior superior (SIP)) and begins at the ischial tuberosity.
    This ligament also plays an important role in stabilizing and moving the ISG. Together with the sacrospinal ligament, it is the strongest ligament for stabilizing the nutation movement.
    The sacrospinal ligament and the sacrotuberous ligament
    make a major and minor sciatic notch Foramen isciadicum major and minor. These are important passageways for vessels, annoy and Muscles represent.
  • Iliolumbar ligament
    They continue up the posterior sacroiliac ligaments and extend from the iliac to the 4th and 5th Lumbar vertebrae . These ligaments are responsible for stabilizing the anterior SI joint area.

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Function of the ligaments as a whole

The ligaments described are the most important structures for stabilizing the SI joint and preventing unphysiological movements in this joint.

If there are malfunctions in the SI joint with incorrect posture or malpositions of the intestinal or sacrum, the affected ligaments are put under increased strain, resulting in an increase in tension in the ligaments, which can lead to a movement disorder of the SI joint.

Provocation tests for the ligaments

The ligaments are tested and provoked in the supine position. Here you bend the patient's leg and stretch the ligaments in different positions of the Hip joint exerts a thrust along the longitudinal axis of the thigh.

  • To test the iliolumbar ligament, guide the knee towards the opposite hip joint
  • To test the sacrotuberous ligament, bring the knee to the shoulder on the same side
  • To test the Ligg. sacroiliaca dorsalia and sacrospinale, the knee is brought to the opposite shoulder.

As a practical tip, it has proven to be beneficial that the Stretching of the ligaments hold it for a while and feel it (palpate).

Innervation of the SI joint (nerve supply)

The sacroiliac joint is mainly supplied from the nerve root S1 (nerve from the sacrum). The Ligg are an exception. sacrotuberals and sarospinals that are supplied from segments S3-4.

Axes of motion

Sacroiliac joint

In the ISG, movements take place around different axes of movement, the intersection of which is at the level of the second sacral vertebra.

  1. Frontal axis
    The flexion and extension movements (bending and stretching) of the SI joint take place around this axis. It is an imaginary line that runs horizontally through the second sacral vertebra.
    The flexion and extension movements are also called nutation and counter-nutation.
  2. Longitudinal axes
    The sacrum rotates around this axis when walking and thus allows slight rotational movements.
    It is a vertical line that divides the sacrum into right and left halves.
  3. Diagonal axes
    These are two axes that run diagonally through the sacrum. The right one runs from the upper right to the lower left pole, the left one from the upper left to the lower right pole.
    Since the torsional movements take place around these axes when walking, they are also referred to as torsion axes.
  4. Sagittal axis
    It is the intersection of most of the axes and runs from the front and back through the second sacral vertebra.
    The sagittal axis is very important for the balance of the sacrum.

Range of motion

The degree of mobility is very low. Active movement is not possible.

Movements while walking

During the Walking there are minimal but changing movements in the SIGs. The movements in the ISG should be made clear by the step with the right leg.

  • At one step with that right leg the right ilium (iliac bone) moves backwards. The ilium rotates around the longitudinal axis to the left, while the left one moves forward. An additional torsional movement (turning movement) around the left torsion axis causes the sacrum base to tilt to the left.
  • From the transition to the middle standing leg phase, the right coxae rotates forwards and the left one backwards. As a result, it turns Sacrum to the right and its base descends on this side.

Practical tip

Testing of joint play and the muscles
In the case of malfunctions in the ISG, it is important whether the cause is a malfunction of the Joint play or the Musculature lies.
Usually both disorders are coupled to each other. Various tests are carried out to examine the joint play. For general understanding, one joint partner is fixed and the other is moved (mobilized). If there is a side difference, it is a matter of reduced joint play on the poorly sliding side. In addition, the associated muscles must be checked for their flexibility.

Muscle training for SIG instability
In the event of joint instability, the SI joint should not be mobilized or manipulated, but rather the corresponding muscles should be trained for stabilization. Of particular importance are the M.erector spinae and the M. piriformis.
Since muscle building usually involves ongoing movement in the ISG, an attempt must be made to prevent this. It is therefore important to first passively stabilize the pelvic ring and only then to train the muscles.

ISG blockage / ISG blockage

One wrong movement can cause very severe pain.

A sacroiliac joint blockage refers to decreased mobility of the sacroiliac joint. SI joint blockade, SI joint blockage (sometimes the joint is also abbreviated as SIG) and hypomobility of the sacroiliac joint are used synonymously. Physiologically, the SI joint has very little mobility and cannot be moved consciously. This joint is held in place by tight ligaments.

Changes to the joint surface (for example, due to wear and tear or diseases associated with inflammation of the SI joint) and the surrounding soft tissues including the ligaments can lead to a blockage of the joint. Often it comes to sudden onset pain in the lower back (lower lumbar vertebrae) and the buttocks. The pain is movement-dependent and can be aggravated by some movements. Some people wake up in pain at night and need to lie down in a different position to relieve the pain. The pain can range from short-term, stabbing pain to dull, permanent pain.
Reasons for a blockage of the ISG can be heavy lifting, overuse during sport, overstretching of the ligaments or unusual movements such as an unwanted "step into the void" when stumbling on the stairs. Monotonous work or unfavorable postures can also lead to an ISG blockage.

Some spinal conditions have a higher risk of blockage of the SIJ. These can be diseases that lead to improper stress on the hip or those that directly affect the sacroiliac joint, such as ankylosing spondylitis, which is very often associated with inflammation of the sacroiliac joint. Inflammatory bowel disease (Crohn's disease, ulcerative colitis) also occurs in some people with inflammation of the sacroiliac joint.
Diagnostically, the so-called pseudoradicular complaints in an ISG blockage must be distinguished from the radicular pattern in herniated discs in the lower lumbar spine. (In the case of a herniated disc, the nerve roots are squeezed as they exit the spinal canal.)
In the case of a herniated disc of the lumbar spine, the SI joint is often blocked. Therefore, if there is a herniated disc of the lumbar spine and an ISG blockage at the same time, the question arises about the hen and the egg!

The exact course of the pain serves as a distinguishing feature. In the case of a herniated disc, these run along a dermatome, that is, along the supply line to the affected nerve root. The pain associated with an SI joint does not adhere to these limits. In addition, the reflexes are not weakened and there is no muscle weakness on the affected side.

From a therapeutic point of view, pain medication to reduce the pain symptoms are initially useful. So-called non-steroidal anti-inflammatory drugs such as ibuprofen or diclofenac are used for this. Muscle relaxants can also help to counteract pain-related tension. Local heat can also help relax muscles. Movement should not be avoided in general. There are some exercises that can help release the blockage by moving the sacroiliac joint. It can happen that you hear a "cracking" sound while moving and the pain subsides a little. The exercise should then not be interrupted, but repeated a few more times. Different exercises can be done alone (see exercises). There are also a few handles that a therapist (e.g. a physiotherapist) can use to release an ISG blockage. This usually reduces the pain, but it may take a few days for it to go away completely.

Read more about these topics at:

  • ISG blockage
  • ISG blocking

Figure ISG - blockage

Figure ISG - blockade: groin pain (left) and back pain (right)

ISG - blockade - conduction symptoms

  1. Sacrum-iliac joint
    (Sacroiliac joint,
    abbreviated ISG)
    Articulatio sacroiliaca
  2. Front Sacrum-iliac ligament
    Lig. Sacroiliacum anterius
  3. Iliac bone - Os ilium
  4. Sacrum - Sacrum
  5. Lumbar and sacrum kink -
  6. Fifth lumbar vertebra -
    Vertebra lumbalis V
  7. First lumbar vertebra -
    Vertebra lumbalis I
  8. Thoracolumbar junction
  9. Twelfth thoracic vertebra -
    Vertebra thoracica XII
  10. Hip joint - Articulatio coxae

    Pain radiation areas:
    A - lumbar spine (lumbar spine)
    B - buttock region - Gluteal region
    C - Groin - Inguinal region
    D - front and back leg
    E - knee

You can find an overview of all Dr-Gumpert images at: medical illustrations

Inflammation of the SI joint / sacroiliitis

An inflammation in the sacroiliac joint is called sacroiliitis in medical parlance. The inflammation in the sacroiliac joint (sacroiliitis) can lead to destruction of the joint with severe pain and the possible consequence of irreversible postural damage. In the last stage of the disease, there is complete osseous stiffening of the joint (so-called ankylosis). An inflammation of the SI joint can be proven by various imaging methods. Magnetic resonance imaging (MRI) is the method that detects changes in the very early stages. More advanced stages can also be seen in classic X-rays and in computed tomography (CT) examinations.

An inflammation of the sacroiliac joint (sacroiliitis) is usually not found as a single disease, but as a symptom of an underlying disease.
Typical underlying diseases associated with sacroiliitis are:

  • the ankylosing spondylitis
  • Behçet's disease
  • Reactive arthritis
  • especially Reiter's disease
  • Psoriatic arthritis
  • inflammatory bowel disease such as Crohn's disease
  • ulcerative colitis.

Bechterew's disease is a rheumatic disease. More men are affected. In addition to inflammation in the sacroiliac joint (sacroiliitis), changes in the spine often occur with increasing stiffening. In addition, inflammation of various joints and the insertion tendons of muscles (for example the Achilles tendon) are typical.

Behcet's disease is particularly common in the Mediterranean region and, in addition to inflammation of the SI joint (sacroiliitis), often has canker sores in the mouth and genital area, various skin rashes, inflammations in the joints and eye diseases as symptoms.
You can find out more about this disease at: Behçet's disease

Reactive arthritis is inflammation of the joint that occurs a few days after the upper respiratory tract becomes infected with the bacterium Streptococcus.

Reiter's syndrome describes the simultaneous occurrence of conjunctivitis, joint inflammation and inflammation of the urinary tract.

Psoriatic arthritis is a special form of psoriasis that is associated with joint inflammation.

In general, the treatment of the underlying disease is in the foreground. Cortisone or other immunosuppressants (such as methotrexate (MTX)) are often used.

Read more on this topic at: Sacroiliitis

ISG syndrome

The ISG syndrome is not uniformly defined. It includes various conditions associated with sacroiliac joint pain. It can therefore be used as a Collective term can be seen, which includes various diseases of the sacroiliac joint. Sometimes the term sacroiliac joint syndrome refers to diseases that lead to chronic complaints. Typical pains are included Back pain, especially in the pelvic area (also Lower back pain). There is also pain in the area of ​​the Buttocks and lateral pelvis and in the Groin in front.

Typical causes of an ISG syndrome are arthrosis as a sign of wear and tear, overstressing and overstressing of the ligament apparatus, inflammation in other underlying diseases (e.g. in ankylosing spondylitis) and by loosening the ligamentous apparatus in women in the pregnancy and after childbirth.
During pregnancy, the loosening of the ligamentous apparatus is a desired and necessary process, as it makes the birth process possible through a somewhat greater mobility within the sacroiliac joint.

Various clinical tests can be carried out as diagnostics if an ISG syndrome is suspected. That is typical Forward phenomenon, in which the examiner on both sides of the standing patient Bony prominence of the pelvis (so-called Spinae iliacae posteriores superiores: you can feel these on the back if you follow the iliac blades from above towards the buttocks). At these points there is also a typical one Tenderness in ISG syndrome. When the patient slowly bends over, an assessment is made as to whether these protruding bones are moving forward evenly on both sides. If this is not the case, this indicates a blockage within the sacroiliac joints. There are a few other clinical tests that induce movement within the sacroiliac joint and the painfulness of these tests suggests SI joint syndrome. The diagnosis can be made in conjunction with typical triggers, such as one-sided posture when sitting or exercising.

Imaging procedures such as roentgen-, CT- or MRI- Examinations are usually not necessary. In the case of complicated processes or the suspicion of chronic inflammation of the SI joint (sacroiliitis) as the cause of the complaints, however, they can be useful in individual cases.

Therapeutically, come first with ISG syndrome conservative Measures under consideration. This includes combating pain with classic Painkillers (for example Ibuprofen). In addition, physiotherapeutic measures and avoiding special stressful situations can help. In severe cases (possibly also CT-controlled) the painful Joint With Local anesthetics and cortisone-like substances are offered. One is also very rare operational Therapy with stiffening of the ISG considered.

Arthrosis of the SI joint

A arthrosis in the sacroiliac joint arises from the heavy load on this joint over years.The sacroiliac joint (also known as the sacrum-iliac joint) connects the spine with the pelvis and is therefore a central point of transmission of the force from the back, head and arms to the pool and the legs. Due to the upright gait, very strong forces are transmitted here. In order to deal with these forces, the joint is secured by very strong and tight ligaments and allows only minimal movements.

The tapes are going through now heavy loads For example, if you are stressed by heavy physical work for years and there is a little more mobility in the joint, rubbing the joint surfaces can lead to osteoarthritis. There the joint surfaces wear out, of the Cartilage becomes thinner, the surface is no longer smooth but rough. With every movement, the rubbing of these rough surfaces creates pain stimuli. In the case of high stress situations, a locally limited inflammation arise, which intensifies the pain (so-called activated osteoarthritis).

Typical symptoms of sacroiliac joint arthrosis are deep back pain, Pain in the buttocks and partially Radiation of pain into the leg. Also Paresthesia in the affected skin area are possible. The symptoms are similar to and can be confused with irritation of the sciatic nerve.

Sacroiliac joint arthrosis is diagnosed by the typical symptoms and a corresponding history. Many too Births can be a risk factor for SI joint osteoarthritis due to the loosening of the ligaments. In addition, a clinical examination is carried out by an experienced examiner. The diagnosis can be supplemented by x-rays.

In the early stages, treatment of pain and controlled movements under physiotherapeutic guidance come into play. Also other conservative treatments like Osteopathy, Stimulation current and acupuncture can help. So-called local infiltration can be used for severe pain. This is done (possibly under imaging control using CT or roentgenFluoroscopy) on and into the joint Local anesthetic often together with one cortisone-like drug injected. In this way, relief can be achieved, especially in phases with particular pain peaks.

As last chance becomes a surgery viewed. This is where the joint Stiffened with screwswhich prevents further rubbing of the two articular surfaces against each other, but to one Loss of function leads.


There are a variety of exercises that can help with sacroiliac joint obstruction. These should be explained in detail by a physiotherapist or orthopedic surgeon and applied after a thorough examination. These exercises help to move the sacroiliac joint and thus to release blockages.

A simple exercise that can be done at home is a pendulum motion in the pelvis. To do this, stand on an elevation (e.g. a thick book) and swing the other leg slightly back and forth. If you move the pelvis of the supporting leg a little forward with one hand while swinging back, you can increase the movement in the ISG. If you have balance problems, you should do this exercise on a wall that you can support yourself with with both hands.

Another exercise in the supine position is, for example, careful cycling. The legs in the knee joint and hip joint are bent at right angles and you make careful circular movements with the legs as when cycling. You can also put both hands under the sacrum while lying on your back and slowly circle your pelvis in all directions.

In the 4-footed stance (kneel supported on knees and hands) the legs are alternately stretched out so that they form a straight line with the back. You can also do the exercise from time to time as a precaution, while at the same time stretching the other arm (i.e. diagonally left leg, right arm) forward.

As a prophylactic measure, you should avoid unfavorable sitting positions, heavy lifting and carrying, and jerky movements in the hip joint. In general, light sporting activity is beneficial to strengthen muscles and tendons and to prevent an ISG blockage.