Biomechanical Study Of Tow Kinds Of Crescent Fracture-dislocation Of The Sacroiliac Joint Fixation

Objective:To research the biomechanics of the different fixations of crescent fracture-dislocation of the sacroiliac joint in cadaveric specimens,We compared the biomechanical stability between the internal fixation by means of interfragmentary screw and reconstruction plate fixation and iliosacral screw fixation,and analyzed biomechanical transmission of tow kinds of fixations round fracture line and sacroiliac joint.Methods:Four normal adult cadaver specimens were selected,removing the redundant soft tissue and retaining the structure of the surrounding ligaments of the sacroiliac joint.Osteoporosis,deformity,tumor and trauma and other abnormalities were exclued by the naked eye and X-ray.Transecting cadaveric specimens from the junction of L4、 5 and the middle part of the double thighs to get experimental pelvic specimens.The specimens was fixed on the electronic testing machine with anatomieal standing position.10 strain units were pasted on proximity of the fracture line and the sacroiliac joint and the values of strain were recorded with digital strain measuring instrument.Electronic testing machine provided 0-500 N of the vertical load to the specimen at the speed of 2mm/min.After making the crescent fracture-dislocation of the sacroiliac joint model,the specimens were fixed successively with the iliosacral screws(two screws at the level of S1)and interfragmentary screw and reconstruction plate fixation(a long cancellous screw and 6 Hole pelvic reconstruction plate and several cortical bone screws).Applying methods above with vertical loading,recorded the vertical displacement and the strain values of different pressure between the two internal fixations.SPSS 22.0 statistical software was used for statistical analysis of the data and the calculation of axial stiffness.We used t test and ANOVA test to analysis results,there was no significant difference when P < 0.05.Results:The biomechanical test showed that: under the same condition of 500 N loads,the mean vertical displacement of interfragmentary screw and reconstruction plate fixation group was less which was 3.765±1.140 mm,when the mean vertical displacement of iliosacral screw group was more which was 3.961±1.180 mm,and two groups did not have statistical differences(P ﹥ 0.05).With different loads,the axial stiffness of iliosacral screw group were entirely greater than interfragmentary screw and reconstruction plate fixation group,the mean axial stiffness of iliosacral screw group was 124.643±46.309N/mm,the mean axial stiffness of interfragmentary screw and reconstruction plate fixation group was 117.036±41.879 N/mm,and the t test showed that they did not have statistical differences(P﹥0.05).Applying vertical load to original pelvic specimens,stress concentration points round fracture line and sacroiliac joint in the main positions: Superior of S1 side of sacroiliac joint 3,4sites;The fracture line and anterior sacroiliac joint lateral intersection 8site;lateral midpoint of midpoint of sacroiliac joint and lineae arcuata 9site.After making the crescent fracture-dislocation of the sacroiliac joint model,fixing the specimens with different fixations and applying vertical load in turn to get the change of biomechanical transmission.Compared to original pelvic specimens group,The change of biomechanical transmission of iliosacral screw group showed: 2,4sites slightly increased,4,7,10 sites were no obviously changes,and they did not have statistical differences(P ﹥ 0.05);1site slightly decreased,3,8,9sites obviously decreased,5site obviously increased,and they had statistical differences(P﹤0.05).the change of biomechanical transmission of interfragmentary screw and reconstruction plate fixation group showed:2,6sites slightly decreased,10 site notablely increased,and they did not have statistical differences(P ﹥ 0.05);1,4sites slightly decreased,3site notablely decreased,9site slightly increased,5,7,8sites notablely increased,and they had statistical differences(P﹤0.05).Conclusions:The biomechanical study made the crescent fracture-dislocation of the sacroiliac joint model and fixed with internal fixation by means of interfragmentary screw and reconstruction plate fixation and iliosacral screw fixation.The results of vertical displacement and axial stiffness showed that tow kinds of fixations had no significant differences.Compared the influence of biomechanical transmission of tow kinds of fixations round fracture line and sacroiliac joint,iliosacral screw fixation was superior to interfragmentary screw and reconstruction plate fixation with vertical loading in biomechanical transmission.