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Sacro Iliac Instability

Illustration showing the location of the sacroiliac joints, anterior and posterior views. © Louise Carrier 2007.

Between 1 and 3 patients out of every 10 with chronic low back pain is likely to have the sacro iliac joint as the source of their pain. In health the joint helps to provide stability to the low back and pelvis whilst buffeting some of the forces during weight bearing and walking. To this end, small movements of the joint are necessary but excessive movements are usually prevented by a relatively rugged contour of the joint surfaces and strong supporting ligaments.

In youth the joint surfaces are relatively smooth and with age the surfaces become more rugged and more immobile. In some instances, over the age of about 60 years, the joint surfaces are bridged by new bone formation and the joint stiffens.

On occasion the joint may cause pain because of the development of osteoarthrosis (degenerative change of the joint surfaces).

On other occasions the joint may become painful because of active inflammation of the joint. In the majority of cases, however, no definite cause for the pain can be proven through investigations but it is likely that pain arises due to a breakdown in the supporting structures that keep the joint stable. This may occur if the ligaments supporting the joint become relatively lax. Lax ligaments are the hallmark of the latter stages of pregnancy, so it is not uncommon for this to develop in females during or after pregnancy. In such instances, however, the ligaments tend to regain their strength gradually several months after the birth of the baby. In a proportion of patients, however, the ligaments remain lax and symptoms remain.

Another group of people who seem to suffer more than their fair share of musculoskeletal problems and who commonly suffer with sacroiliac pain are those who are hypermobile. See Benign Joint Hypermobility Syndrome.In these people, there is a tendency for a number of joints to be “loose” and unstable due to a generalised laxity of the supporting ligaments.

Other possible causes of sacro iliac joint instability may arise from a direct fall onto the buttock with resulting sprain and stretching of the ligaments or the problem can develop gradually due to repetitive movements such as bending and lifting.

Clinical Features

Pain is often felt overlying the sacroiliac joint but can radiate into the groin or anywhere into the lower leg. Pain is seldom felt in the midline of the low back or above the level of the pelvis. Pain tends to be worse when in one position for any length of time and there may be frequent, or infrequent exacerbations of more severe pain, when it may be difficult to take weight through the sacro iliac joint such as when sitting or walking. On occasion this may be associated with a feeling of the leg giving way.


Sacroiliac joint instability may be treated through exercise, manipulation and bracing of the joint. Injections into the ligaments using sclerosing solutions (prolotherapy) may be of benefit when usual treatments are not working.