| Objective:(1) To compare the biomechanical difference between embalmed human femur and PMMA femur.(2) To compare the biomechanical difference of fixing artificial femoral neck fracture between dynamic sleeve three-wing screw and three hollow screws.(3) To explore the biomechanical stability of dynamic sleeve three-wing screw for treatment of femoral neck fracture by the three-dimensional finite element analysis (FEA).Methods:(1) Select the mechanics model for single foot standing, preload the specimen5times in the Instron-8874hydraulic servo mechanical testing machine, each specimen is tested5times, every test should be interval20min, record data when changes in values of the strain gauge is less than3με. Under the total loading of1200N, with100N multi-step incremental cycling loading, the speed of testing machine was controlled10mm/min. Observe the relation between load and strain、 load-displacement and resistance to load deformation capacity of femur head.(2) Ten artificial PMMA femoral model were selected, and the central neck of the specimens was sawn with a electric saw at Pauwels angle of70°to form adduction type femoral neck fracture model. After anatomic reduction, fix the specimens respectively with three hollow screws and dynamic sleeve three-wing screw according to the operative approach. Instron-8874servo-hydraulic mechanical testing machine was used to fix the specimens which simulated uniped standing. Select15key points on proximal femur as test points and give the model gradation loading at the rate of10mm/min with linear load0～1200N. The strain of each points under1200N load, head sink displacement under different loads and the strain of8points on pressure side were measured.(3) We established models of femoral neck fracture with Pauwells angle30°,50°and70°, fixed by dynamic sleeve three-wing screw based on reverse engineering and CAD software, and used finite element analysis software to simulate the human femoral head stress modes.Results:(1) The load exhibited linear change with strain under2times body weight loading in embalmed and artificial specimens; The displacement of artificial specimens was greater than embalmed specimens (P<0.01); but the resistance to load deformation capacity of embalmed femur specimens was larger than artificial femur specimens (P<0.01).(2) There was a peak at the eight resistance strain gage at1200N load, the strain values of three hollow screws and dynamic sleeve three-wing screw were (-756±14) and (3024±127)με, showing statistically statistical significance (P<0.01). Under the same load, the head sink displacement in the group of dynamic sleeve three-wing screw was greater than the hollow screws group (P<0.01). The strain values at the eight resistance strain gage in the group of dynamic sleeve three-wing screw was larger than the other group under the same load, showing statistically statistical significance (P<0.01), and the strain values became higher with the increase of load at the same fixation group.(3) Stress and strain concentrated near the broken ends of fractured bone, and degressed for both sides form fracture. Von mises stress of dynamic sleeve three-wing screw in different phases are much less than the yield strength of titanium alloy (896MPa).Conclusions:(1) The deviation of PMMA artificial bones and human bones is relatively large, but the formers could reflect the trend of the human femur specimens. Experimental study on the biomechanics often needs lots of femoral specimens, in the femur specimens obtained increasingly difficult conditions, it is feasible to replace embalmed femur specimens to a certain extent in biomechanics experiment.(2) Dynamic sleeve three-wing screw has good biomechanical stability for treatment of femoral neck fracture which illustrate the feasibility of clinical application from the mechanical experiments.(3) We established models of femoral neck fracture with Pauwells angle30°,50°and70°, fixed by dynamic sleeve three-wing screw to simulate the human femoral head stress modes. There is good agreement between finite element analysis and biomechanical study, and dynamic sleeve three-wing screw has good biomechanical stability and axial pressure effect. |
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