Optimal insertion point of reverse sacral alar-iliac screws in sacroiliac joint fixation for Tile type C pelvic fracture and its preliminary clinical application
Objective To explore the optimal insertion point of reverse sacral alar-iliac screws(RSAIS)in sacroiliac joint fixation for Tile type C pelvic fracture and the effectiveness of its preliminary clinical application.Methods CT data from 90 patients with no abnormal pelvic structures in the Radiology Department database of Liyang People's Hospital from January 2022 to January 2023 were selected.There were 45 males and 45 females,aged 21-69 years[(45.5±6.4)years].With CT digital reconstruction technology,the RSAIS fixation was simulated and the anterior insertable area was measured.Five insertion points were at the ilium-acetabular recess in the area superior posterior to the acetabulum(A1),at 1 cm(A2)and 2 cm(A3)posterior transversal to A1,at 1 cm(A4)and 2 cm(A5)inferior longitudinal to A1.With the entry point of S,pedicle screw as the exit point,the transverse and sagittal CT scans were conducted on 5 screw trajectories of anterior posterior lines(corresponding to five groups).The anatomical parameters of the screw trajectories,including the length,width and height of the screw trajectories were measured by two observers independently and the intraclass correlation coefficient(ICC)between the observers was analyzed.Tile type C pelvic fracture models were established from 20 3D-printed L5-pelvis-femur specimens and divided into 5 groups,with 4 specimens in each group.The anterior rings were fixed with cross screws while the posterior rings with one RSAIS in each group using one of the aforementioned 5 screw trajectories.The overall displacement and local displacement of the sacroiliac space under 300 N vertical load in all the groups were measured with a biomechanical machine.The screw trajectory was designed according to the optimal insertion point shown in the above anatomical measurements and mechanical experiments.An RSAIS with a diameter of 7.3 mm was inserted percutaneously to treat a patient with Tile type C1 pelvic fracture.The fluoroscopy time of screw insertion and screw position were recorded as well as bone reunion,numerical rating scale for pain,Oswestry dysfunction index(ODI)and Majeed functional score of pelvic fracture at the last follow-up.Results The anterior insertable area was(1236.64±12.04)mm2.The trajectory lengths for the three transversal insertion points gradually decreased from front to back,with A1 being the longest(104.9±10.4)mm,followed by A2(98.5±9.8)mm and A3 the shortest(92.7±9.7)mm(P＜0.01),while there were no significant differences in the widths or heights(P＞0.05).There were no significant differences in the length,width or height of the screw trajectories of the three longitudinal insertion points(groups A1,A4 and A5)(P＞0.05).Compared with A4 and A5,A1 was farther from the margin of the acetabulum.The range of ICC of the anatomical parameters of the 3 screw trajectories measured by the two observers was 0.88-0.98,95％CI 0.90,0.96,and 95％CI 0.95,0.99,indicating high consistency.After the screws were placed and fixed at the 3 transversal insertion points,the overall displacement and local displacement of the sacroiliac space of groups A1,A2 and A3 gradually increased from front to back.They were(2.93±0.09)mm and(1.49±0.14)mm in group A1,(3.14±0.12)mm and(1.63±0.54)mm in group A2 and(3.23±0.12)mm and(1.67±0.67)mm in group A3 respectively.There was a significant difference in the overall displacement among three groups(P＜0.01),while the local displacement of the sacroiliac space in group A1 was decreased compared with that of group A2 and A3(P＜0.01).After the screws were placed and fixed at the 3 longitudinal insertion points,there were no significant differences in the overall displacement and local displacement of the sacroiliac space of group A1,A4 and A5(P＞0.05).The fluoroscopy time of RSAIS inserted from A1 for the treatment of patients with Tile C1 pelvic fracture was 66 seconds,with fine screw position.At the last follow-up,the fracture was healed,with numerical rating scale for pain decreased from 6 points preoperatively to 1.ODI improved from 41 preoperatively to 18,and the Majeed functional score of 81 points.Conclusions For Tile type C pelvic fracture,the screw trajectory from the iliac-acetabular recess located in the superior anterior part of the insertable area is the longest,with the best stability and relatively good safety of the screw,making it the optimal insertion point for RSAIS.The effect of preliminary clinical application of RSAIS from the optimal insertion point is satisfactory.
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