Biomechanical Comparison Of Four Kinds Of Posterior Pelvic Ring Fixation Methods

Backgrounds and Objectives: The purpose of this study is to compare four kinds of fixation method(TIILS, ISS, TIFI and TBLP) for posterior pelvic ring by biomechanical test.Methods:(1)6(3 male, 3 female) frozen normal adult body specimens of the pelvic were selected to the experiment. Retaining the major ligaments and embedding them with fixation instruments.(2) Intact specimens of the pelvis were firstly taken on material testing machine((MTS 858 Mini Bionix Ⅱ, MTS Systems, Inc, Eden Prarie, MN) for vertical condensation and torsinal mechanics, stress-strain and spin-torque data was collected.(3) Tile C type of pelvic fracture models were made by the method as follow: separate pubic joint by using pendulum saw, and fix it with a 5 hole locking plate, then the pelvic specimen was made a left Denis II type fracture of sacra, followed by taking ISS, TBLP, TIFI, TIILS fixed. Each fixiation method was followed by loading test and torsional test, at the same time the stress-strain and the and the torsion-torque data were recorded.(4) Data were analysed by using R language. The continuous data were curve fitted and required r quare value >99.5%. The data which predicted from the fitted curves according to multiple vertical strain under pressure and torsion angles were taken to Kruskal-Wallis test and multiple comparison between groups.Results: All 6 specimens met the expected requirments and successfully passed the test. In statistical analysis, all the r quares of the curve fitting have met the expectation of >99.5%. The analysis of the 161 pressure points’ prediction of vertical strain value indicated that TBLP and TIFI showed significant difference with normal pelvic stability(P<0.05), but no statistical differences between the four fixation methods. At the same time, the stress-strain curve revealed that the vertical stress stability from strong to weak follows ISS, TIILS, TBLP, TIFI. The analysis of the 169 torsion angle points’ prediction of torque value showed no statistical differentce between the four kinds of fixation methods and the intact pelvis(P>0.05). And the ability to resist the torsional stresses of the four fixation methods from strong to weak follws TIILS, TIFI, ISS, TBLP, which can be seen from the torsion-torque curve.Conclusion: Four fixation methods of the posterior ring of pelvis can all provides stable fixation, but the stability of ISS and TIILS are better than TIFI and TBLP. Because the ISS is difficult to inserted in a right location and more risky in the operation, whereas TIILS affords minimally invasive fixation as well as high security and easy to manipulate, TIILS fixation hope to become a more ideal choice to fix the posterior pelvic ring.