| ObjectiveThe biomechanical effects of two cross screws(Φ 6.5 mm)combined with anterior small plate(Φ 2.7 mm)fixation methods were compared with three screws(Φ 6.5 mm)fixation,anterior plate(Φ 3.5 mm)fixation and anterior plate(Φ 3.5 mm)combined with posterolateral screw(Φ 6.5 mm)fixation commonly used in ankle arthrodesis to verify the safety and stability of two cross screws combined with anterior small plate fixation in ankle arthrodesis,in order to provide a theoretical basis for subsequent clinical application.MethodsA 64-slice spiral CT was performed on the right foot and ankle of a healthy adult male volunteer with a slice thickness of 0.625 mm,and the obtained tomographic image data were output and stored in DICOM format.Reading was performed via Mimics software to obtain volunteer ankle image information and preliminarily establish a rough three-dimensional ankle model.Geomagic software was then used to smooth and denoise the three-dimensional model of the ankle joint to achieve surface optimization of the three-dimensional model of the ankle joint.Then Solidworks software was imported for assembly cutting,simulation of ankle fusion surgery and other operations,and four kinds of finite element analysis experimental models of ankle fusion were established:(1)two cross screws combined with anterior small plate fixation model;(2)three screw fixation model;(3)simple anterior plate fixation model;(4)anterior plate combined with posterolateral screw fixation model.Finally,the above four models are imported into the finite element analysis software Ansys to set the analysis parameters and loading conditions,and the fusion surface displacement,model stress peak and stress distribution of the above four models in response to internal rotation(torque 10 N · m),external rotation(torque 10 N · m),back flexion(bending moment 10 N · m)and neutral(vertical 2,100 N · m)stresses are obtained.Finally,the biomechanical efficacy of the four ankle fusion fixation methods is comprehensively compared and analyzed.Results(1)Displacement of fusion surface: When two cross screws combined with anterior small plate fixation methods resist four stresses: dorsal flexion,neutral,internal rotation,and external rotation,the maximum displacement produced by the fusion surface is less than the other three fixation modes.The maximum displacement produced by the fusion surface of the simple anterior plate fixation model after applying the above four loads was significantly greater than that of the other three fixation models.Under neutral and back flexion stresses,the maximum displacement values of the fusion surface of the three screw fixation models were greater than those of the anterior plate combined with posterolateral screw fixation model,while under medial and external rotation stresses,the maximum displacement values of the fusion surface of the three screw fixation models were less than those of the anterior plate combined with posterolateral screw fixation model.(2)Stress peak and stress distribution: According to the overall stress peak of the four models,when counteracting external rotation and internal rotation stresses,the stress peak produced by the two cross screws combined with anterior small plate fixation model and the three screw fixation model was smaller than that produced by the anterior plate fixation model and the anterior plate combined with posterolateral screw fixation model,and when counteracting neutral(vertical)and back flexion stresses,the stress peak produced by the two cross screws combined with anterior small plate fixation model and the anterior plate combined with posterolateral screw fixation model was smaller than that produced by the three screw fixation model and the anterior plate fixation model.Among them,the peak stress value of simple anterior plate fixation under four loads is the largest model.From the peak stress values of bone,plate and screw in each of the four models,the risk of broken nails,broken plates and stress fractures was greatest in the two cross screws combined with anterior small plate fixation models and the three screw fixation models during vertical stress,and the risk of broken nails,broken plates and stress fractures was greatest in the simple anterior plate fixation model and the anterior plate combined with posterolateral screw fixation model during internal and external rotation stress.From the stress distribution of the four models,most of the stresses were concentrated in the middle of the compression screw,the plate-screw junction,and the plate bending site.ConclusionTwo cross screws combined with anterior small plate fixation has more biomechanical advantages than three screw fixation,anterior plate fixation and anterior plate combined with posterolateral screw fixation,and the use of two cross screws combined with anterior small plate as a fixation device in ankle arthrodesis is a safe and reliable internal fixation method. |
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