Duck gait or wobble gait is a common sign of congenital medullary dislocation. In unilateral dislocation, lameness appears, and in bilateral dislocation, the pelvis is tilted forward when standing, the hips are shrugged back, the waist is convex, and the abdomen is bulged, so it is called duck gait or wobble gait when walking from side to side, and it is easy to fall down when walking slightly fast. The clinical examination methods in early childhood are as follows. 1.Nelaton line: the line between the anterior superior iliac spine and the sciatic tuberosity passes through the apex of the greater trochanter when normal, called the Nelaton line, and the greater trochanter is above this line when the hip joint is dislocated. 2.Trendelenburg test: ask the child to stand on one leg and bend the other leg as far as possible, so that the foot is off the ground. When standing normally, the contralateral pelvis rises; after hip dislocation, the femoral head cannot hold the acetabulum and the gluteus medius muscle is weak, causing the contralateral pelvis to fall, which is especially clear when observed from behind, which is called a positive Trendelenburg test and is a sign of hip instability.