| ObjectiveThe S2-alar-iliac(S2AI)screws have been described as an alternative method for lumbosacropelvic fixation in place of iliac screws.Although the S2AI screw technique has been widely used in spine surgery,its application in pelvic fractures is still poorly understood and lacks relevant mechanical theoretical guidance.The purpose of this study was to evaluate the biomechanical stability of S2AI screw and S1 pedicle screw fixation(S2AI-S1)in the treatment of sacral fractures through finite element analysis and biomechanical research methods.In addition,preliminary clinical results of S2AI-S1 in the treatment of unstable posterior pelvic ring injuries are reported.MethodsThe Denis type Ⅰ and Ⅱ pelvic fracture models were constructed in the finite element analysis study.The anterior pelvic ring was fixed with five-hole plate,and the posterior pelvic ring was fixed with unilateral lumbopelvic fixation(LPF),transiliac internal fixator(TIFI),sacroiliac screw(SIS)fixation,S2AI-S1 fixation and S2AI screw and contralateral S1 pedicle screw fixation(S2AI-CS1).Four different loading methods were implemented in sequence to simulate the force in standing,flexion,right bending and left twisting,respectively.Vertical stiffness and relative displacement were recorded and analyzed;In the biomechanical study,28 intact artificial pelvis models were randomly divided into four groups(N=7),and then made into Denis Ⅱ sacral fracture and pubic symphysis injury models.The posterior pelvic ring was fixed with LPF,SIS,S2AI-S1 and S2AI-CS1,respectively.Each model was cyclically tested under increasing axial compression.Optical motion-tracking was used to assess relative displacement and the number of failure cycles;In a clinical study,25 patients with unstable posterior pelvic ring injuries received S2AI-S1 fixation.The length of incision,operation time,blood loss,intraoperative fluoroscopy times,reduction quality,postoperative complications and functional outcomes were recorded and analyzed.ResultsIn Denis type Ⅰ and type Ⅱ sacral fractures,the vertical stiffness predicted by the finite element model in the five groups were S2AI-S1,SIS,S2AI-CS1,LPF and TIFI from large to small.The overall average relative displacement of the five groups of models is TIFI,LPF,SIS,S2AI-CS1 and S2AI-S1 groups from large to small in Denis Ⅰ model.In the Denis Ⅱ model,the overall average relative displacement from large to small were LPF,TIFI,S2AI-CS1,SIS and S2AI-S1 groups;In the biomechanical study,in terms of relative displacement at the 4800th cycle,the mean values of the LPF,SIS,S2AI-S1 and S2AI-CS1 groups were 22.85 mm,4.80 mm,3.73 mm and 14.74 mm,respectively.In terms of the number of failure cycles,the LPF,SIS,S2AI-S1 and S2AI-CS1 group averages were 5561,8677,8310 and 5768,respectively.In the pairwise comparison,there was no statistical significance between the S2AI-S1 group and the SIS group,and there was a statistical significance between the S2AI-S1 group and the LPF group and between the S2AI-S1 group and the S2AI-CS1 group;In the clinical study,a total of 29 groups of S2AI-S1 fixation were used in 25 patients.The average incision length was 8.3 cm,the average operation time was 86.4 minutes,the average number of intraoperative fluoroscopy was 7.9,and the average blood loss was 148 ml.The mean postoperative follow-up time was 17.8 months.Satisfaction with the quality of pelvic reduction was 25/29,and the average Majeed score at the last follow-up was 81.5.At the last follow-up,all patients’ fractures healed,and there were no obvious signs of screw protrusion,screw loosening,or internal fixation failure.ConclusionsCompared with SIS,LPF and TIFI groups,S2AI-S1 group has better mechanical stability in Denis type Ⅰ and Ⅱ sacral fracture models.The S2AI-S1 fixation,not including the lumbar spine in the fixation range,is a simple,safe,and effective fixation method.When the S1 pedicle screw insertion point on the affected side is damaged,S2AI-CS1 can be used as an appropriate alternative to S2AI-S1. |
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