Preparation and portal making. (A) Place the patient supine on the traction table. (B) Position the hip to be operated on in extension, approximately neutral abduction, and 15° of internal rotation. (C) Landmarks outlined: femoral artery (FA); greater trochanter (GT); and anterior superior iliac spine (ASIS); optimal needling line (ONL). (D) Apply traction to the operative extremity, and confirm the correct position of the Kirschner wire as a metal marker for the optimal needling line. (E) Fluoroscopically, a vacuum sign, seen as a crescent-shaped area of radiolucency, appeared in the distracted affected hip and the Kirschner wire centered between the acetabulum-femoral head space. (F) The ONL was depicted along the Kirschner wire course on the skin with a marker pen. (G) Three modified portals were referenced from the optimal needling line - the anterior, anterolateral (AL), and posterolateral (PL) portals. (H) Establish the anterolateral portal first, and further distention is achieved by forcibly injecting 30 to 50 ml normal saline into the joint space.