Abstract: Objective To explore the entering spot, the length , the diameter and the direction of the iliac screw in the lumbopelvic fixation operations and provide anatomic basis for implanting correctly the iliac screw. Methods A total of 35 side hipbone specimens of native adults were studied.There were 30 side male specimens and 5 side female,16 left sides and 19 right sides.One line from the arc of the notch between posterior superior iliac spine and posterior inferior iliac spine was difined as the baseline(a).It was extended to acetabulum edge.Another line(b) was marked through the ischial spine and anterior superior iliac spine.It was intersected with baseline(a) in C spot. The C spot was located on the surface of ilium body behind the acetabulum and determinated.The fan-shaped lines were described in the posterior part of iliac through the C spot and the baseline.Five oblique sections were obtained through there fan-shaped lines. Various oblique sections were observed and correlation data above the 10°-30° oblique sections were measured.At the same time,the medial lip, lateral lip and intermediate line in the behind part of iliac were observed.After definiting the entering spot, the length, the diameter and the direction of the iliac screw,these data were verificated in 2 native adut cadavers . Results It was found that 35° oblique section arrivals to the iliac fossa and 5° oblique section clings to the arc of the greater sciatic notch. The diameter of the iliac screw based on f line which was the shortest distance between the gluteal surface and pelvic surface. The intermediate line on posterior part of the iliac spine could be distinguished clearly,which was like a regular arc and the most raised part. The minimum distances(K) from entering spots to the cartilage of the acetabulum roof was 109.38mm.  Conclusion Iliac screws can be implanted accurately and safely by the C spot,the baseline and the outer plate in 10°-30° posterior part of the iliac. The most entering spots are located in the points of the fanshaped lines intersecting with the

Key words: Lumbopelvic fixation, Iliac screw, Applied anatomy, Human