Biomechanical Analysis Of External Fixation For Unstable Pelvic Fracture With Pin Purchased In The Anterior-inferior Iliac

Objective: Pelvic fracture is usually caused by high-energy injury,itmakes the pelvic vertically and rotationally unstable. High-energy injuries tothe pelvic ring are frequently associated with significant soft tissue injury andblood loss with hemodynamic instability. Immediate pelvic external fixation isan effective component of resuscitation of these patients, and it may work bydecreasing pelvic volume, minimizing motion between disrupted fracturesurfaces or joints, allowing for tamponade of ongoing venous bleeding anddecreasing the mortality rate. Traditional frames are constructed withanterosuperior pin placement into the iliac crest, it could provide sufficientstability to the anterior ring of the pelvic. However, anterior external fixatoralone is unlikely to adequately stabilize the disrupted posterior pelvic ring. Inunstable vertical shear fractures, the external fixator is not sufficient to resistthe longitudinal force applied on the posterior pelvic ring without excessivedisplacement. Recently external fixation of the pelvic ring with pin placementinto the dense supraacetabular bone in the region of the anterior inferior iliacspine has gained popularity. Anterior inferior pin placement wasbiomechanically superior to conventional anterior-superior pin placement invertically unstable fractures. But it is controversial for the pin fixing directionin the treatment of unstable pelvic fracture. Our aim is to provide thetheoretical basis on selecting optimal fixing direction in the treatment ofunstable pelvic fracture according to biomechanical comparison in differentfixing direction of the pelvic external fixator which pin purchased in theanterior-inferior iliac spine of supraacetabular area. The another purpose ofour experiment is to discuss stability of the posterior pelvic ring when theAIIS-AIIS distance is closer than anatomic positioning of the AIISs. Methods: Slected3embalmed cadaveric specimens.The spacimen allwere from men, along with their spine intact from the forth lumbar vertebra tothe sacrum. The proximal2/3of femora,the intact najore pelvic ligaments, andintact hip joint were obtained. All of the three specimens were visuallyexamined and then X-rayed、CT scan to exclude the disease of pelvic bonesuch as obvious osteoporosis、tuberculosis、tumor and other pathologicabnormality. The pelvis was cleaned off soft tissues and muscles, retained theintegrriyy of the symphysis pubis and bilateral SI joint、 hipjoints、sacrotuberous ligament and sacrospinous ligament,removaled intervertebraldiscs of forth lumbar vertebra with mixed denture base resin. Thus, A Type C1injury was created. Our test divides into four groups: GroupA: The pinperchased in the anterior inferior iliac spine to the area within the SupraSciatic great Notch1.0cm. GroupB: The pin perchased in the anterior inferioriliac spine to the area above the Supra Sciatic great Notch1.0-2.0cm. GroupC:The pin perchased in the anterior inferior iliac spine to the area above theSupra Sciatic great Notch2.0-3.0cm. GroupD: The pin perchased in theanterior inferior iliac spine to the area above the Supra Sciatic great Notch3.0-4.0cm. Four displacement would be measured. S1: displacement of thepubic symphysis in all the groups. S2: displacement of the SI joint in all thegroups. S3: displacement of the SI joint in all the groups when the AIIS-AIISdistance0.5cm closer than anatomic positioning of the AIISs. S4:displacement of the SI joint in all the groups when the AIIS-AIIS distance1.0cm closer than anatomic positioning of the AIISs. During the testingprocedure，the specimens were kept moist with saline solution to decrease theorganism denaturation owing to the test,so that the experimental result wereprecise and commeasurable. After each test,let the specimen revert to theinitial state by taking a5minute rest in order to eliminate the effect because ofthe creep.Results: With the load pressure gradually increased, the movement ofsacroiliac joint and symphysis pubis ara gradually increasing.1Didplacemenr of the pubic symphysis between all the groups(S1) The data shows that there was no significantly different between thegroup A、B、C、D in controling pubic symphysis separation, but the pubicsymphysis displacement of groupB (The pin perchased in the anterior inferioriliac spine to the area which above the Supra Sciatic great Notch1.0-2.0cm)issmaller than those of other groups under the different load in our test.Didplacement of the SIjoint between all the groups(S2)Compared with the sacroiliac joint displacement of group B and groupD, statistical significant difference was shown between them. But there wasno significantly different between the group A、B、C in controling SI jointseparation.That means the SI joint displacement of groupB (The pinperchased in the anterior inferior iliac spine to the area which above the SupraSciatic great Notch1.0-2.0cm)is smaller than those of other groups under thedifferent load in our test.Displacement of the SI joint in each four groups（S2,S3,S4）When the AIIS-AIIS distance0.5cm closer than anatomic positioning ofthe AIISs, there was significantly different in the group D in controling SIjoint separation.S2and S3). When the AIIS-AIIS distance1.0cm closer thananatomic positioning of the AIISs, there was significantly different in all thegroup in controling SI joint separation（S2and S4）. In all the groups,Compared with the displacement of the SI joint in all the groups when theAIIS-AIIS distance0.5cm closer than anatomic positioning of the AIISs(S3)and the displacement of the SI joint in all the groups when the AIIS-AIISdistance1.0cm closer than anatomic positioning of the AIISs(S4), statisticalsignificant difference was shown between them.Conclusion: Based on the results of this study for TileC1pelvicfracture, there was no significant diffrences between four fixing directions incontrolling the pubic symphysis separation. In controling SI joint separation,there was no significantly different between the group A. B.C Between thefour fixing direction, there was significant diffrences between the groupB andgroup D. When the pin perchased in the area within the Supra Sciatic greatNotch1.0cm, it is very likely to penetrate the iliac bone into the pelvic cavity. So,we suggest that the best fixing direction is above the Sciatic great Notch1.0-3.0cm. In our test, When the AIIS-AIIS distance0.5cm closer thananatomic positioning of the AIISs, there was significantly different in thegroup D in controling SI joint separation.(S2与S3). When the AIIS-AIISdistance1.0cm closer than anatomic positioning of the AIISs, there wassignificantly different in all the group in controling SI joint separation(S2与S4).So, the pelvic external fixator with the pin perchased in theanterior-inferior iliac spine was not always provide greater stability. If weover compressed to the pelvic ring, it may even aggravate unstable of thepelvic ring posteriorly. So, it is better to use the external fixator for thetemporary fixation, once the patient conditions allowed, we should useinternal fixation to stabilize the pelvic ring.