The 4-character test is a clinical test commonly used to examine the hip and sacroiliac joints. When the test is performed, the limbs of the body form a shape similar to the 4 in the Arabic numeral, which is called the 4-character test. The person should be placed in a lying supine position with the head, torso and limbs in a horizontal line. The ankle of one lower limb is placed on top of the knee of the other limb, and the examiner uses one hand to press on the anterior superior iliac spine on one side and the other hand to press on the knee of the lower limb on the examining side, with both hands pressing simultaneously. If the patient describes pain in the lumbosacral or hip joints, the four-letter test is positive, suggesting a lesion or injury to the hip or sacroiliac joint.