The Measurement Of The Screwing Trajectory's Parameters Of The Sacroiliac Screw For Iliosacral Joint Disruption By The Computed Tomography

Objectives: To explore a more accurate and simple method which measures the screwing trajectory's parameters of the sacroiliac screw by the computed tomography,so as to provide the related theoretical basis for the safty of the sacroiliac screw path during the iliosacral screw fixation for iliosacral joint disruption.Method: 20 pelvis specimens(40 sacroiliac joint)of native adults were studied.The iliosacral screw fixation had been taken on all pelvis specimens,and then the CT scans were done.The screwing trajectory's parameters of the sacroiliac screw were measured,including the distances from the inserting point of to various structures of pelvis,such as the inserting direction of the guidewire,the length from the inserting point and the safty angle.Results:1 The diameter of the deal screw was(20.54±1.41)mm,and the length was(86.92±1.81)mm.2 The diatance from the entry point to the crista glutea,the greater sciatic notch,the posterior superior iliac spinethe,posterior inferior iliac spine,the contrary anterior cortex of vertebral body,the central part of vertebral body,and the most narrow part of pedicle of vertebral arch were(20.12±2.98)mm,(40.42±2.01)mm,(36.98±1.59)mm,(37.41±1.32)mm,(86.96±4.21)mm,(71.61±3.93)mm,and(52.42±2.98)mm,respectively.3 The angles of the ideal screw was(25.06±1.12)° to coronal plane,and(20.01±1.52)° to the horizontal plane.4 The angles between guidewire and iliac surface in axial CT scans and in coronal CT scans were(90.62±3.67)° and(90.47±2.99)°.5 The safe angle of the screw trajectory was(24.51±1.67)°to the axial plane,and(19.62±1.61)to the coronal plane.Conclusion:1 The techinque of the sacroiliac screw fixation for iliosacral joint disruption has the advantage of small trauma,quickly recovery and little cost,which was a simple and accurate method.2 For the effective internal fixation obtained after using S1 screw,a sacroiliac screw with a diameter of 6-7mm and a length of 65-70 mm was more efficient for the fixation.The angle modulation decreased with the increase of the length and the diameter of the screw.The angle formed between the screw and the coronal plane was 25.06°,and he angle formed between the screw and the horizontal plane was 20.01°.3 The screw parameters varied according to the individual anatomy.The measurement of the screwing trajectory's parameters of thesacroiliac screw through the computed tomography before the operation of internal fixtion,could provide a safe,simple and accurate method for the percutaneous placement of sacroiliac screw fixation for iliosacral joint disruption.