The Trendelenberg sign is used to detect Gluteus Medius and Minimus muscle weakness. To perform this test, ask the patient to stand with her feet shoulder width apart. Place each of your thumbs on the patient’s posterior superior iliac spines. Next, ask the patient to stand on one leg and observe the motion of the pelvis. If your thumbs do not change position, there is adequate Gluteus Medius and Minimus function. If one of your thumbs drops, indicating that one side of the pelvis is sagging, the test is positive and the Gluteus Medius and Minimus are weak on the opposite side.