Applied anatomy of percutaneous fixation using sacroiliac screw

Objective: To provide anatomic basis for percutaneous fixation using sacroiliac screw. Methods: 50 adult dry sacrum and 30 pelvic specimens were used. The contour of sacrum and relationship between axis of pedicle and auricular surface of sacroiliac joint were observed. The height and thickness of S1,S2 pedicle, and other operation parameters were determined. The inserting point for the screw on ilium was ascertained, and the neighbour structures around the point were observed. Optimal angle and distance for the screw through the S1, S2 pedicles were also determined on 50 cases of CT film. Results: The height and thickness of S1 pedicle was(22.1±4.6)mm and(27.8±3.1)mm, the height and thickness of S2 pedicle was(13.4±3.6)mm and(20.9±2.2)mm respectively. The S1 inserting point on out lamellar of ilium lay(3.1±1.2)mm around the point which was on the crossing point of posterior-middle third of the line from anterior superior iliac spine to posterior superior iliac spine. The S2 inserting point lay(4.2±1.7)mm around the point which was on the crossing point of anterior four-fifths and posterior one-fifths of the line from iliac tubercle to posterior inferior iliac spine. The optimal angle of S1 pedicle axis with sagittal plane was 55°, for S2 was 80°, with coronary plane for S1 was 36°, for S2 was 15°. Conclusions: (1)S1 pedicle could hold 2 sacroiliac screws whose diameter is around 6.5～7.0 mm, while S2 pedicle could only hold one. (2) The angle of screw with sagittal plane for S1 was 55°, for S2 was 80°, with coronary plane for S1 was 36°, for S2 was 15°. The optimal depth of screw for S1 was 68mm, for S2 was 55mm. (3) The operation of percutaneous fixation using sacroiliac screw should be strictly defined on the condition when iliosacral dislocation was completely reducted.