Objective To introduce an efficient way to orientate S1 iliosacral screw guide-pin verified by CT.Methods The pelvic axial CT data in DICOM format of 180 adults between July 2017 and June 2018 were retrieved from the database of Imaging Center,Luoyang Orthopaedic Hospital of Henan Province.The data were input into the software Mimics 20.0 to display the axial,coronal and sagittal sectional views of the pelvis.On the axial CT sectional view displaying the largest osseous pathway in the S1 segment,a virtual iliosacral screw and its virtual guide-pin were accurately placed into the sacral body in an oblique fashion.In the design of ideal insertion,the virtual screw and guide-pin were truly in the pelvic transverse plane when they were located exactly in the pelvic axial CT sectional view,and they intersected the outer iliac table at the start-point which restricted the guide-pin's location,and angulated with the pelvic coronal plane (represented by a line connecting the most dorsal points of bilateral ilia) at an angle (α) which limited the guide-pin's orientation.After three-dimensional pelvic models of the standard lateral sacral view and the pelvic outlet and inlet views in each patient were calculated,they were displayed in a transparent manner using the software,followed by the virtual insertion of the screw and guide-pin.After the start-point was established on the standard lateral sacral view,the guide-pin was orientated into the pelvic transverse plane and at the guide-pin's α angle relative to the pelvic coronal plane,and subsequently inserted into the ilium shallowly for stabilization.The pelvic outlet and inlet views were taken to judge the guide-pin's orientation.If fine orientation was verified,the guide-pin was advanced to its final position,followed by virtual insertion of an iliosacral screw over the guide-pin.After the virtual insertion was completed,the axial,coronal and sagittal CT sectional views of the pelvis were scrutinized to evaluate the accuracy of insertion.Results After all the guide-pins were orientated in the 180 adults (360 sides) on the true sacral lateral view according to the above way,their orientations on the pelvic outlet and inlet views were 100％ fine,leaving further adjustment unnecessary.The intraosseous insertions of the virtual screws and guide-pins were 100％ accurate and safe on the CT sectional images.Conclusion The way introduced here can theoretically guarantee accurate orientations of the guide-pin on the pelvic outlet and inlet views with no more complex guide-pin adjustments,assuring insertion accuracy and enhancing surgical efficiency.

Objective To evaluate the safety and accuracy of modified percutaneous retrograde intramedullary screwing into the superior pubic ramus or anterior acetabular column for pelvic and acetabular injury.Methods A retrospective analysis was conducted of the 23 patients with pelvic and acetabular injury who had been treated with modified percutaneous retrograde intramedullary screwing into the superior pubis ramus or anterior acetabular column from June 2015 to June 2017 in Luoyang Orthopaedic Hospital of Henan Province.They were 12 men and 11 women,aged from 22 to 88 years (mean,53 years).The injury included 17 pelvic fractures,4 acetabular fractures,and 2 acetabular plus pelvic fractures.The safety and accuracy of screwing were assessed by postoperative physical and imaging examinations.The number of fluoroscopy and operative time were documented for each retrograde intramedullary screwing into the pubic symphysis or acetabular anterior column.The quality of fracture reduction was evaluated by the Mata criteria postoperatively.The Majeed and the Harris scores were used to evaluate the functional recovery of the pelvis and acetabulum at the last follow-ups.Results A total of 31 intramedullary screws were placed in the 23 patients.For insertion of one screw,the operative time ranged from 15 to 50 min (average,35 min) and the number of fluoroseopy from 32 to 55 times (average,45 times).Postoperative physical examinations revealed no iatrogenic neurovascular lesion and uneventful healing of incisions in all the patients.Postoperative imaging examinations showed that 29 screws were located completely in the bone and 2 ones protruded the cortical bone of the pubic anterior border;all the screws did not protrude into the acetabulum or broke through the pubic symphysis or the pubic cortex.By the Matta criteria,the postoperative fracture reduction was rated as excellent in 17 cases,good in 5 and fair in one,giving an excellent to good rate of 95.7％.Of this series,19 were followed up for 6 to 24 months (mean,13 months).All the fractures healed after 3 months.The Majeed scores at the last follow-up for the 13 patients with pelvic fracture were excellent in 12 and good in one.The Harris scores at the last follow-up for the 6 patients with acetabular fracture (including the 2 with pelvic fracture) were excellent in 5 and fair in one.Conclusion The modified percutaneous retrograde intramedullary screwing into the superior pubic ramus or anterior acetabular column is safe,convenient and precise,effectiyely reducing radiation and operative time.