Located between the sacrum (tailbone) and ilium (hip bone) in the pelvis, the sacroiliac (SI) joint (Fig. above and below) is a common but frequently overlooked source of low back pain. SI joint pain is not specific to any particular age group, occupation, or sporting activity.

Establishing the diagnosis
Diagnosing SI joint dysfunction can be difficult because the symptoms and physical findings of this condition are also seen in other well-recognized causes of low back pain (including a herniated, or slipped, disc). Your physician can diagnose SI joint dysfunction by carefully reviewing your clinical history and performing a thorough physical examination. Plain x-rays, CT, and MRI are not usually helpful in establishing the SI joint as a source of low back pain, other than ruling out back pain that may be caused by a disc herniation, pinched nerve, inflammation, or infection.

Symptoms
The main symptom is a sharp or aching pain in the lower back, usually to one side. This pain is frequently felt in the groin (Fig. 2A) and usually extends down the back of the thigh and occasionally as far as below the knee (Fig. 2B). SI joint pain is increased when you are sitting for long periods of time (such as in an automobile or during a long plane ride) and is frequently alleviated by standing or walking. Rarely are there associated neurologic problems in the lower extremities (knee, leg, foot), such as numbness, tingling, or weakness.

Physical findings
Although there is no direct method for isolating SI joint dysfunction during a physical examination, there are several tests that can help your physician localize the pain in the SI joint during examination (Click on Figs. 3, 4, & 5 for details on these examinations).

Treatment
Most patients can be successfully treated by SI joint manipulation, mobilization, and a prescribed exercise routine to maintain joint mobility (see Rehabilitation of the Sacroiliac Joint). Temporary use of nonsteroidal anti-inflammatory drugs (such as ibuprofen) or occasional joint injection may be helpful. Studies are now being conducted to discover the advantages of surgically fusing a sacroiliac joint that has not benefited from conventional treatment, but surgery is generally a last resort for patients who continue to have pain.

If you have any current back problems, such as sharp pains or constant stiffness, don't hesitate to see your physician. With proper treatment, you can get "back" to a normal, healthy lifestyle.