A positive 4-character test means that the patient lies in a supine position, with the limbs relaxed and the upper limbs on both sides against the body, bending one knee at an angle of 90° or even greater, letting the ankle joint of the bent side of the knee rest on top of the knee joint of the unbent side and near the thigh, doing a movement similar to crossing the legs. Then the examiner presses the bent knee and the unbent hip with both hands, pressing down at the same time, and if there is pain in the hip or the posterior lumbosacral area, it is called a unilateral 4-character test; if both limbs have pain during the examination, it is called a bilateral 4-character test. a positive 4-character test may indicate hip synovitis, femoral head necrosis or sacral The 4-character test is an examination method used by doctors to determine whether a patient has a sacroiliac joint lesion or a hip lesion.