Biomechanical Characterristics Of Studying On Femoral Shaft Fracture In The Internal Fixation With Interlocking Intramedullary Nail By Optical Measurement Method

Objective:Optical measurement method was applied to basic biomechanical study on the femoral shaft fracture in the internal fixation with interlocking intramedullary nail,the value of the displacement and deformation of intramedullary nail at the mark line of femoral shaft and four locking nails under the conditions of different tensile and different group in this issue were measured,and the changes of displacement and deformation were analysed. Aimed at providing the mechanical basis for optimization program of the femoral shaft fracture in the internal fixation with interlocking intramedullary nail.Materials and Methods:1.experimental object:Four native femoral specimens of male corpses aged 20-40 which were fixed by 10% formalin provided by Department of human anatomy of Kunming Medical College were used, left or right side was at random.2. experimental model and group:After all soft tissues of the samples were removed,and emoral full-length, outside diameter and inside diameter on average were measured respectively by (45.25±3.54) cm, (2.69±0.32) cm, (1.11±0.16) cm. Interlocking intramedullary nails were placed inside the femoral shaft marrow located in the lateral of intercondylar fossa from bottom to top,and four locking nails were through four layers of cortical bone.The distal tips were coated by dental base acrylic resin powder. The femoral shaft midpositions were desected vertically by the scroll saw to make the fracture model. The locking nails namedⅠ,Ⅱ,Ⅲ,Ⅳfrom top to bottom.In this experiment,five conditions were designed for every specimen:A The femur was not sawed with interlocking intramedullary nail placed inside the femur shaft marrow (simulation of the cured fracture); B The femur was sawed on the basis of A in order to simulating a stable fracture (the center point of femoral shaft was sawed up one time);C The more complicated fracture was made on the basis of B in order to making the bone fracture 5cm far from the middle fracture line based on group B;D The locking nailⅠof the upper distal end was removed based on C; E The locking nailⅣof the lower distal end was removed based on D; Then specimens were fixed and installed on CSS-44100-electronic universal testing machine.The load of 50N was applied in advance to remove the loosening and creeping. Subsequently, the axial load was applied 0～500N at 10N/s and the computer recorded the bias automatically. The calculation of the displacement and deformation was based on the digital speckle correlation method (DSCM) when it was applied 500N.In the experiment,we could attain some data which were dealed with by statistical software SPSS 11.5 and were denoted in the form of (x±s).We evaluated these data by analysis of variance with repeated measures for overall statistical analysis. P<0.05 was considered significant.Results:1.Analysis of the displacement and the deformation of intramedullary nail at the mark line of femoral shaft by analysis of variance:Tensile load at 100N-500N, the comparison of group A and group D,E; the comparison of group B and group D,E; the comparison of group C and group E; tensile load at 200N-500N, the comparison of group C and group A,E; there were significantly different(P<0.05); the comparison of the other groups were no significant difference (P>0.05)2. Analysis of the displacement and deformation of four locking nails by analysis of variance:the comparison of locking nailsⅠandⅡ, there was no significant difference at 100N-500N (P>0.05),and the comparison of the other locking nails are no significant difference (P<0.05),and the displacement and deformation of four locking nails and the tensile load were positively correlated.Then the value of displacement and deformation of four locking nails wasⅢ>Ⅳ>Ⅱ>Ⅰunder condition A,B,C when it applied a tensile load of 500N.Conclusion:1.Digital Speckle Correlation Method was an effective optical measurement technique. By introducing this method to the empirical study of biomedicine, the development of medical research could be improved, which implied DSCM was an important method deserving generalization.2.When the treatment of femoral shaft fracture with interlocking intramedullary nail was used,the two distal locking nails were easy to collapse,especially the one was beside the mark line of femoral fracture.