The 4-character test is positive if there is pain in the posterior lumbosacral region, which is located at the area between the lowermost edge of the lumbar region and the uppermost edge of the buttocks. 4-character test is also called the cross-leg test and sacroiliac joint separation test, which is a test to check whether there is a lesion in the sacroiliac joint. Specifically, the patient should lie on his or her back with one ankle joint on top of the knee joint of the other leg in a cross-legged or crossed-legged motion, while the doctor presses the immobile hip with one hand and the knee joint of the crossed leg with the other hand, using both hands simultaneously. If there is pain in the above location, the 4-character test is positive, which means that the patient has damage or lesions in the sacroiliac joint, such as joint damage, rheumatoid arthritis, bone tuberculosis and other diseases. However, in some patients, the 4-character test will show pain in the crotch, indicating that the femoral head or hip joint is diseased.