SI joint

The SI joint (sacroiliac joint) lies between the sacrum and the pelvic half (ilium). The body has two SI joints, both left and right of the sacrum. These joints ensure that forces from the legs are transferred to the back and vice versa.

Anatomy of the SI joint

The two SI joints are part of the pelvic girdle. The pelvis is therefore important for the stability and mobility of the SI joints. The shape of the bones, the ligaments, and the muscles provide stability for the SI joint. The mobility of the SI joint is only 2 to 4 mm in all directions, which is very little.

Various sheets of connective tissue (fasciae) run over the pelvis. Together with the muscles attached to the pelvis, they provide even more strength.

SI joint pain

SI joint pain is mainly felt on the pelvic rim and in the buttock region. The pain can radiate towards the thigh or the groin. The symptoms are very similar to low back pain. SI problems are therefore often mistakenly considered to be low back pain.

Causes of SI joint pain

The pain is usually caused by instability in the entire pelvis. The best-known form is pelvic instability during pregnancy. Causes of SI joint pain are:

• Hard fall on the buttocks.
• Deterioration in the quality of the cartilage.
• Joint inflammation.
• Pregnancy.
• Reduced stability in the pelvis.
• Leg length discrepancy.
• A scoliosis (sideways curvature) in the spine, which the pelvis has to correct.
• Previous back surgery in which vertebrae were fused.

SI joint complaints or low back pain?

It is sometimes very difficult to determine whether the pain comes from the SI joint. This is often not detectable by X-ray, ultrasound imaging, or MRI scan. The patient's story and various physical tests give the best clues.

An injection can optionally be placed in the SI joint. If this provides relief, it is clear that the symptoms come from the SI joint. If the injection does not relieve the pain, the cause lies elsewhere.

Treatment for SI joint complaints

There are many different treatments for SI problems. Treatment by the physiotherapist mainly consists of exercises aimed at restoring movement and stabilising the entire pelvis.

There are also other treatment options, such as:

• A pelvic belt. This provides extra stability to the pelvis and is mainly used in pelvic instability during or after pregnancy.
• Injection into the SI joint. This mainly helps in cases of osteoarthritis and inflammation of the SI joint.
• iFuse surgery. In this procedure, one or both pelvic halves are fixed to the sacrum with a pin.