Fig. 2

a Locater (A1) is fixed to the obturator crest entry point of acetabular anterior column b Locater (A2) is fixed to the posterior column of ilium outside entry point. c The X-ray of the guide apparatus form the rectangle structure and the guiding needle enters the opposite locater (the guiding needle enters the opposite locater by passing through the obturator crest entry point (E) and the posterior column of the ilium outside the entry point (D))