The cross iliac joint is the connecting link between the pelvis and the spine. Due to the everyday heavy use of this body region he has an important function. The high load on the joint, however, also favors the easy emergence of painful complaints.

What is the cross iliac joint?

With cross iliac joint (also called sacral iliac joint,

The sacroiliac joint - short: ISG, sacro-iliac joint) is the bilateral articulation of the sacrum and the ilium.

The joint is between the 1st and 3rd sacral vertebrae. Since it is surrounded by tight bands that limit the range of motion, it is a so-called "amphiarthrosis" (Greek: amphi = around, and arthros = joint). Occasionally, due to its minimal mobility, the ISG is also referred to as an "unreal" joint.

In addition to the cross-iliac joint, the joints between the foot and carpal bones are also among the amphiarthroses. Despite its limited internal flexibility, the sacroiliac joint plays an important role in the entire musculoskeletal system of humans. Here, ultimately, the power transmission of upper body and legs takes place.

Anatomy & Construction

The sacral bone consists of five inter-vertebrae and forms the stable base of the spine. It is located above the coccyx, below the lumbar vertebrae. The ilium makes up a large part of the pelvis, extending from the iliac crest to the hip joint. The L-shaped cross iliac joint connects the two bony surfaces ( facies auricularis ) of these bones. As with all joints, they are each covered with articular cartilage ( sacroiliac ligament ) and connective tissue fibers and are surrounded by firm, supporting ligaments. The sacroiliac joint lies in a narrow joint cavity and has only a small joint space. It is designed only for the transmission of low forces, the surrounding bands must compensate strong strong forces and pressure accordingly, so as not to overload the joint.

The nature of the cross-iliac joint changes in the course of life depending on the sex. In men, the flexibility of the joint decreases with advancing age - up to the joint blockade. The reason for this is an increasing irregularity of the still smooth texture of the bony surfaces in young people. In women, the sacroiliac joint remains relatively more mobile, but even here it comes to age-related signs of wear.

Function & Tasks

The ilium and sacrum support the entire load of the upper body and are thus heavily used parts of the human musculoskeletal system. The cross iliac joint as its junction thus also plays an important role. It helps to transfer the weight of the upper body to the lower limbs and is part of the elastic stabilization of the trunk.

Supported by tight fibers and ligaments, the sacroiliac joint, despite its joint function, has almost no room to move, as it mainly has force-transmitting functions. The flexibility of the joint is limited to only 1-2 ° rotary movement or 2-4 mm movement in each direction (so-called nutation and Gegennutation). The heavy use of the lower back requires this tight fixation. Especially in a sedentary posture, the joint is heavily stressed in everyday life.

In some circumstances, a sacroiliac joint may be more mobile than the opposite half of the body. In addition to anatomical causes, this functional asymmetry may also be due to one-sided movement stress. Basically, female cross-iliac joints have a higher mobility, since the nature and location of the colliding articular surfaces are more functional than in men.

This circumstance plays an important role, especially at birth. As a result of hormonal effects during birth, the ligaments that fix the joint soften and thus allow stretching of the joint zone. This increases the diameter of the pelvis and facilitates the passage of the child.

Diseases & complaints

According to research, pathological changes in the region of the iliac crest are responsible for up to 25 percent of lower back pain. People with a predisposition to weak ligaments are particularly at risk of developing diseases in the area of ​​the joint.

Overstretched ligaments can lead to an over-mobility of the joint due to a lack of support function. This promotes degenerative changes, such as bony hardening, which is a countermeasure of the body to stabilize the joint.

Also rheumatic complaints are common in the area of ​​the sacroiliac joint and can sometimes cause severe pain. In particular, complaints related to ankylosing spondylitis often occur in this body region.

Finally, abrupt movements during physical activity or in the event of accidents can lead to lesions or painful discomfort on the sacrum and iliac joint. Often, incorrect lifting of heavy loads or "kicking into the void" will result in injury to the joint and may result in so-called ISG blockages.

Long periods of sitting in the workplace, lack of exercise and untreated foot, knee and hip deformities can permanently damage the joint. Inflammations, strains and other diseases of the sacroiliac joint are characterized by sometimes severe, often unilateral and local pain in the buttocks area. The pain can radiate into the inguinal and lumbar region.

Accompanying it may come to tingling and other discomfort. Often, the symptoms occur mainly in a sedentary posture, while walking and standing are painless possible. Targeted training of the surrounding muscles can help relieve the cross-iliac joint and thus relieve the symptoms. In addition, pain-relieving syringes and possibly also surgical interventions may be appropriate.

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