The most common cause of SI joint pain is Sacroiliitis.
Sacroiliitis is an inflammation of one, or both, of the sacro-iliac joints located where the lower spine connects with the pelvis. Though it rarely requires surgery, Sacroiliitis can cause pain in the buttocks or lower back that can extend down into the legs. Often, patients suffering from this condition will experience pain after extended periods of standing, walking or climbing.
Since sacroiliitis is a condition caused by inflammation, there are a number of issues that can cause it. These include:
Wear and tear arthritis, also known as osteoarthritis, can occur within the sacro-iliac joints as can ankylosing spondylitis, an inflammatory form of arthritis that affects the spine.
Traumatic injury such as a fall or car crash that affects the buttocks, lower back or hips.
Pregnancy can cause inflammation as a result of the widening and stretching of the sacro-iliac joints to prepare for childbirth. On top of this, the weight gained during pregnancy can put excessive amount of stress on the joints and lead to abnormal wear.
In rare occasions, infection can occur in the sacro-iliac joints or an infection in a separate part of the body can cause inflammation in the joints.
Patients can experience the symptoms of sacroiliitis in a number of different ways, however it commonly is related to the amount of pressure or stress that is put on the sacro-iliac joint. Common causes include:
Standing for long periods of time
Transitioning from sitting to standing