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    For 15% to 30% of people with long-term lower back pain, one of the sacroiliac (SI) joints, which connect the pelvis with the spine, is the source.

    But it’s not always easy for people or their doctors to identify the SI joint as the problem. Although the sacroiliac is one of the largest joints in your body, it’s buried deep inside your pelvis. Its location makes it hard for doctors to spot any issues during a physical exam. It can also be tough for imaging tests to capture the high-quality pictures that can show it.

    SI joint problems can be confused with other painful conditions, like sciatica and hip arthritis, and routine exams can't always pinpoint what’s really going on.

    Doctors usually rely on the results of three or more tests to diagnose SI joint dysfunction. You can have most of them in your doctor's office.

    Tests in Your Doctor's Office

    Your doctor will start by asking you about your medical history and doing a physical exam, including checking your posture and how well you walk. Then he’ll do some tests to see where the pain may be coming from and how well your SI joint moves.

    Some of the more common tests include:

    Cranial shear test: While you lie on your stomach on an exam table, the doctor puts pressure on your tailbone to check for pain.

    Flamingo test: The doctor asks you to stand on the leg where you have pain and hop.

    Gaenslen's test: While you lie face up, your doctor bends and presses one knee toward your chest while pressing the other leg, outstretched, off the side of the table.

    Gillet test (one-leg stork test): You stand with your feet about 12 inches apart, one leg raised and bent. The doctor stands behind you and pushes on each side of your tailbone with his thumbs, checking for correct movement.

    Pelvic compression test: While you lie on your side, the doctor presses down on your upper hip.

    Pelvic distraction test: While you lie face up on the table, the doctor presses down on both sides of your pelvis at the same time.