The significance of individual measuring by preoperatively application of helical computed tomography in the placement of screw on the sacroiliac joint

Objective To explore the feasibility of individual measuring the parameters of the screwing trajectory of the screw on the uninjured side by application of helical computed tomography before open reduction and internal fixation using sacroiliac screw to guide the placement of screw on the injured side.Methods(1) Ten frozen pelvic specimens of normal Chinese adults were scanned and multiplanarly reconstructed by helical computed tomography in order to measure the entrance direction of the S1 screw,the distance from the entry point to the posterior superior iliac spine and the posterior inferior iliac spine,the length,and safe angle of the screwing trajectory as well.(2) The left and right sacroiliac joints of eight pelvic specimens were made into vertical unstable model.Then,the left sacroiliac joints were individually validated by the iliosacral screws according to the measurement result of the screw trajectory scanned by CT on the right sacroiliac joints,and the right sacroiliac joints by the measurement results of the screw trajectory on the left side.Results(1)The direction of screw was(25.95±1.39)° to the coronal plane,and(19.61±2.97)° to the horizontal plane.The distance from the entry point was(37.17±2.90) mm to posterior superior iliac spine,and(38.23±1.69) mm to the posterior inferior iliac spine.The safe angle of the screw trajectory was(19.87±1.61)° to the coronal plane,and(23.84±2.08)° to the axial plane.(2)All of the ten inserted iliosacral screws of the left sacroiliac joints inserted were entirely within the pedicle;In the right side,except one deviated out of the bone,other nine cases were entirely within the pedicle.Conclusions The method through individual measuring the parameters of the screwing trajectory of the screw on the uninjured side by application of helical computed tomography before open reduction and internal fixation using sacroiliac screw to guide the placement of screw on the injured side has been proved a reliable method.