| ForewordIntercondylar fracture of humerus which is common style in distal humerus fracture, it is part of articulation fracture. At present, There are a lots of internal fixation treatments in intercondylar fracture of humerus, as yet, there are a few of studys in biomechanics and Tree-dimensional finite element analysis. Thus we did a biomechanical comparison of three kinds of internal fixation in intercondylar fracture of humerus, and discussed the virtues and faults of the nternal fixation, so as to provided the theoretical basis for clinical practice. Then we set up an intact Tree-dimensional finite element model of distal humerus by photshop and 3D-DOCTOR software, base on the model we analyzed stress of distal humerus with Tree-dimensional finite element analysis and verify the correspondent relationship between stress and structure under the position.Objective: 1. A biomechanical comparison of three kinds of internal fixation in intercondylarfracture of humerus ,so as to provided the theoretical basis for clinical practice.2. To estabish a Tree-dimensional finite element model of the distal humerus of normal person as a foundation of finite element analysis in this area.3. To analyze stress of distal humerus with Tree-dimensional finite element analysis and verify the correspondent relationship between stress and structure under the position.Materials and Methods1. 18 fresh humerus specimens were harvested ,all of them were male .they were made "T" style intercondylar fracture of humerus and then were mounted in Polymethylmethacrylate (PMMA).2. According to the objectives above,the 18 fresh humerus specimens were theated as 3 groups, different fixations were applied for specimens, The first group was fixed Kirschner wire add "8" wires , The second group was fixed single "Y" type plate, The third group was fixed 1/3 tubular plate and 3.5cm reconstruction plate. All of humers specimens3. In course of strain gauge choice, Strain-binding choice, intercondylar parenchyma of humerus clearing, surface clearing, lineation, Strain gauge adhibiting, solidify, down-lead link, quality test and defending to adhibit two (total four) side the fracture line.4. The indentation tests were conducted using a material test system (MTS,model:Mini Bionix, USA). The indenter with a rate of lN/min, the maximum indentation is 500N. To obtain the average displacement data when the tests repeat six time. After that, SPSS was used to analyze the stress and displacement data.5. To join the four strain gauges of the humerus specimens with TY-20,and thetests were performed using 100N to 500N outside force, and then, to obtain the average strain data when the tests repeat three time. SPSS was used to analyze the stress and strain data.6. To compute the angular rigidity of the specimens using strain and displacement data and analyze the angular rigidity and strain data.7. Distal humerus was used as specimen.The fresh CT scans of humerus were performed and transformed into tiff image format. Bone contours were extractes slice per slice from the stack of 167 tomograms with a slice increment of lmm. The volume of skull reconstructed with 3D-DOCTOR software and then its surface was smoothed. The Tree-dimensional finite element model was gotten.8. Then the model was introduced into ANSYS, we try to determine border condition, subsequently add load, calculate and illustrate stress distribution, strain and displacement of "T" style intercondylar fracture of humerus.Result1. We can conclude from the data of the stress and displacement that 1/3 tubular plate and reconstruction plate was the best, crossing Kirschner wire add "8" wires was better than single "Y" type plate. Displacement of 1/3 tubular plate and reconstruction plate was 0.91mm "Y" type plate was 1.69mm, crossing Kirschner wire add "8" wires was 1.72mm when they were under 500N stress. One-way ANOVA was used to analysis the displacement data. The comparison between first group and second group was 47 percent, and third group was 46 percent (ANOVA, P<0.05), however there were no different between second group and third group (ANOVA, P>0.05).2. The result of strain three different internal fixation methods show that the 1/3 tubular plate and reconstruction plate and the single "Y" type plate were prior tothe crossing Kirschner wire add "8" wires (ANOVA, P<0.05). the experimental and theoretical results show that the stress of ectocondyle and entocondyle became bigger, the stress of intercondylar became smaller.3. The result of the angular rigidity of three different internal fixation methods under 500N stress show that 1/3 tubular plate and reconstruction plate was 549.5 ±0.5 N/mm, the single "Y" type plate was 295.9 + 0.4 N/mm and crossing Kirschner wire add "8" wires was 290.7+0.4 N/mm. The angular rigidity of the 1/3 tubular plate and reconstruction plate was the best (ANOVA, P<0.05)., the single "Y" type plate was better than crossing Kirschner wire add "8" wires(ANOVA, P>0.05)4. The volume of humerus reconstructed with 3D-DOCTOR software. The Tree-dimensional finite element model was gotten and then its surface was smoothed.5. We can conclude from the result of strain and stress of Tree-dimensional finite element analysis that the intercondylar were prior to the entocondyle, ectocondyle and elbow joint, and moreover, the ectocondyle is better than entocondyle. The experimental results of Tree-dimensional finite element analysis show that the displacement of ectocondyle and entocondyle became bigger, the intercondylar became smaller. The result of angular rigidity of Tree-dimensional finite element analysis show that the intercondylar is the biggest, the entocondyle is better than the ectocondyle.Conclusion:1. We can conclude from the biomechanical study that 1/3 tubular plate and reconstruction plate was best, no matter stress-displacement, stress-strain and stress-angular rigidity under the same load condition, it was an good internalfixation and has proper design and stability, but it is not easy to insert. The single "Y" type plate is better than crossing Kirschner wire add "8" wires in stress-displacementm data and stress-angular rigidity data, however, there were no different on stress-strain data of 1/3 tubular plate and reconstruction plate. The crossing Kirschner wire add "8" wires was worse. All of those maybe have a very important relationship between material of internal fixation and dissection of human distal humerus.2. The experimental results and clinic theory all show that the stress of ectocondyle and entocondyle became bigger, the stress of intercondylar became smaller, and stress of ectocondyle is the biggest. It is very important that dissection of human distal humerus and biomechanical of elbow joint.3. It is reliable and accurate to build three-dimensional finite element model with CT scan data. This method is more simpler and efficient than other methods, and can accurarely simulate real and complicated geometry figure.4. We can conclude from the Tree-dimensional finite element analysis that the intercondylar was a weakness-place of distal humerus, so we must choose hard internal fixation methods when it broken. Fracture concrescence would be better with the help of hard internal fixation material. The ectocondyle was stress focus area of distal humerus, it had been proved by biomechanical experiment and clinic.
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