Applied Anatomic Study Of The Parameters Of Screw Fixation For The Sacroiliac Joint

1. BackgroundIn the majority of cases, The pelvic fracture was due to a road traffic accident and falls. The most frequent dorsal pelvic ring fractures associated with fracture of the ischiopubic bones were injuries to the iliosacral joints and sacral fractures. Anatomical reduction and rigid stabilisation are the keys to satisfactory functional and radiological outcomes. In vertically unstable pelvic disruptions, fixation of both the anterior and posterior lesions give more stability and decrease the chance of reduction lossIn vertically unstable pelvic fractures, a variety of procedures have been published for the treatment of pelvic ring fractures including anterior plate fixation, spring plate, sacral bar, lumbopelvic distraction pondylodesis, TSRH, and triangular osteosynthesis. Matta and Saucedo introduced screw fixation for thetreatment of sacroiliac dislocations or sacral fractures. His technique consists of open reduction through a posterior approach and fixation with two screws placed through the iliosacral joint into the body of the SI vertebra. The highest fixation strength is achieved when the screws are positioned in the vertebral body. In recent years, the use of iliosacral screws in managing vertically unstable fractures has been popularised and the early results are quite promising have been reported by Matta and Saucedo. Correct positioning of the screws is technically demanding and relies on identification of anatomic landmarks. Misplacement of the screws may reduce the strength of fixation and additionally lead to neurologic "or vascular complications. Failure rates from 2% to 13% have been reported. To enhance the safety of iliosacral screw fixation, applied anatomic study of the parameters of screw fixation for the sacroiliac joint were done in this laboratory study2. Objective:(1) To provide anatomic basis for iliosacral screw fixation at the level of the pedicle of the first sacral vertebra (SI).(2) To provide anatomic basis for iliosacral screw fixation at the level of the pedicle of the second sacral vertebra (S2).3. Methods(1) Slide gaud and the universal bevel protractors were used inthis laboratory. 22 pelvis specimens of native adults were studied, for a total of 44 sacroiliac joint Anthropometric measurement were performed on 22 cadaveric pelvises to determine the shape of S1 pedicle transverse section, the optimal entry point for iliosacral screw on the outer table of the posterolateral ilium, the direction of screw, and the distance from entry point to contrary anterior cortex of S1 vertebral body.(2) Anthropometric measurement were performed on 22 cadaveric pelvis to determine the optimal entry point for sacroiliac screw on the outer table of ilium, the direction of sacroiliac screw, the diameter of the sacroiliac screw path, the distance from entry point to the center of S2 vertebral body, the distance from entry point to the center of S2 pedicle, and the shape of the S2 pedicle transverse section.(3) After confirming the optimal entry point, verify the different methods for inserting iliosacral screw on 5 fresh pelvises specimens. 4. Results(1) The average entry point for screw fixation on the outer table of ilium located 28. 7mm(15. 0~34. 5)mm anterior to posterior inferior iliac spine and 15. 3mm(10. 0~22. 0)mm superior to the sciatic notch. The results of anatomic measurement of the diameter of the sacroiliac screw path, the distance from entry point to the center of S2 vertebralbody and the distance from the entry point to the center of S2 pedicle were 11. 5mm(8. 5~14. 0)mm, 64.7mm (55. 3~77. 6)mm and 53. lmm(45. 3~ 64. 8)mm respectively. The direction of screw perpendicular to midsagittal plane. The angle between the direction of screw and the outer table of ilium is 62.4 (55~72) in transverse section. Theshape of S2 pedicle transverse section is triangle. (2) The shape of S2 pedicle transverse section is almost ellipse.The broad and height of the pedicle of S1 were 27.7 2.0mm and 20. 2 2. 3mm respectively. The optim...