| Objective: Pelvic fracture is usually caused by high-energy injury,it makes the pelvic vertically and rotationally unstable.There has been so many reports on this kind of fracture,especially the TileC1 pelvic fracture is vertically and rotationally unstable by reason of semi-pelvic injury,so the key of treatment is anterior and posterior pelvic fixation.Reconstruction plate is applied to the superior surface of the symphysis will afford excellent stability.In a sacroiliac dislocation, iliosacral screws inserted offer excellent fixation and damage to soft tissues is minimal.But it is controversial for the stability of one or two iliosacral screws fixation.The purpose of this experiment is to compare the stability of one or two iliosacral screws in sacroiliac dislocation,provide a theoretical basis for clinical treatment.Methods: Selected 12 embalmed cadaveric specimens,including 10 males,2 females,aged 30-58 years with a mean (44.67±10.76) years of age;muscle and soft tissue were removed,the sacrotuberous ligament, sacrospinous ligament and one side of sacroiliac joint ligament were preserved.None of pelvics had any gross strustural or radiological abnormalities.No osteoporosis were found through Osteocore3-EXA-type absorptiometry (Medileink,Inc,FRA) line of bone mineral density measurements.All specimens were cutted between the lower lumbar vertebrae of 4 and 5,and bilateral femurs were cutted off on the middle-lower 1/3.All specimens were sealed with double layer plastic film,cryoprotected at -20oC and thaw at room temperature for 24 hours before the experiment. The experimental sacroiliac joint were distributed by random number table,8 specimens were chosen the right sacroiliac joint and 4 specimens were chosen the life sacroiliac joint.Every specimen was sectioned the symphysis and one side of sacroiliac joint as TileC1 pelvic fracture.12 specimens were divided into 4 groups.Group A: A four-hole reconstruction plate was applied to the superior surface of the symphysis,one iliosacral screw was inserted into the vertebral body of S1.Group B: A four-hole reconstruction plate was applied to the superior surface of the symphysis,two iliosacral screws were inserted into the vertebral body of S1.GroupC: The pubic symphysis was not stabilized, one iliosacral screw was inserted into the vertebral body of S1.GroupD: The pubic symphysis was not stabilized, two iliosacral screws were inserted into the vertebral body of S1.The sacroiliac joint displacement was measured in the 4 groups. The lumbar vertebrae of 5 and the bilateral distal femurs was fixed on the self-made fixture by the mixing appropriate type II denture base polymers,then installed in the CSS-44020 biomechanical testing machine for axial compression test.100 N vertical preload was carried out for 3 times,in order to eliminate the creep effects of specimens.The YJY-17-type extensometer was installed on the both sides of sacroiliac joint.The experiment was loaded to 400 N(upper body weight generally),the rate was 10N/s,recorded the extensometer data.Increasing the load to 800 N,the rate was 10N/s, recorded the extensometer data again.SPSS13.0 statistical sofeware were used for statistical analysis,with t-test and P value was set at 0.05 for the statistical significance.Result: A reconstruction plate was applied to the superior surface of the symphysis. At a load of 400N,the sacroiliac joint displacement of group A was (4.532±0.211) mm and group B was (4.490±0.251) mm, P=0.837>0.05,no statistical significant difference was shown between the two groups. At a load of 800N,the sacroiliac joint displacement of group A was (9.328±0.389) mm and group B was (7.352±0.589) mm, P=0.008<0.05, statistical significant difference was shown between the two groups.The pubic symphysis was not stabilized, At a load of 400N,the sacroiliac joint displacement of group C was (7.552±0.174) mm and group D was (6.648±0.147) mm, P=0.002<0.05,statistical significant difference was shown between the two groups. At a load of 800N,the sacroiliac joint displacement of group C was (13.939±0.560) mm and group D was (11.029±0.551) mm, P=0.003<0.05, statistical significant difference was shown between the two groups.Compared with the sacroiliac joint displacement of group A and group C, one iliosacral screw was inserted into the vertebral body of S1. At a load of 400N, statistical significant difference was shown between the group RP (reconstruction plate) and the group NRP (no reconstruction plate)(P=0.000<0.05);At a load of 800N, the statistical significant difference was also shown between the two groups(P=0.000<0.05).Compared with the sacroiliac joint displacement of group B and group D, two iliosacral screws was inserted into the vertebral body of S1. At a load of 400N, statistical significant difference was shown between the group RP (reconstruction plate) and the group NRP (no reconstruction plate)(P=0.000<0.05);At a load of 800N, the statistical significant difference was also shown between the two groups(P=0.000<0.05).Conclusion: Based on the results of this study for TileC1 pelvic fracture,at a load of 400N,we can conclude that when a reconstruction plate is applied to the symphysis,no significant difference is shown with one or two iliosacral screws,but at a load of 800N,two iliosacral screws increase the stability than one.When the pubic symphysis is not fixed, two iliosacral screws can increase the stability of TileC1 pelvic fracture.No matter one or two iliosacral screws fixation,it can increase the stability by use of anterior and posterior fixation together.
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