| Objective To verified the effectiveness of iliac crest bone grafting procedure in the treatment of recurrent shoulder anterior dislocation by applying a finite element modeling analysis,and to observe the effects of different motion states on glenohumeral stability and graft contact compress as well as exploring the biomechanical mechanism of shoulder glenoid remodeling after bone grafting.MethodsOne patient who underwent iliac crest bone grafting procedure was selected,whose case information and imaging examination results were collected.Utilizing engineering software such as Mimics,3-Matic,NX and Ansys workbench to perform a 3D model and finite element pre-processing based on CT data.The finite element models of the healthy shoulder and the affected shoulder were established respectively and set to a total of 4 different working conditions including abduction 60°,abduction 90°with external rotation movement of 0-90°,simulating the actions that could easily lead to anterior shoulder dislocation.After finite element pre-processing and calculating,we were able to observe the changes of joint stability and stress distribution to verify joint stability after surgery by comparing the displacement of the humeral head.By observing the stress distribution and displacement of iliac crest bone graft,we expected to predict the trend of bone block remodeling process and find out the biological mechanism of bone resorption.Results1.Under the two working conditions of the healthy shoulder joint finite model:(1)The humerus can slide on the glenoid surface under both working conditions,and the humerus displacement changes stably with the movement time.(2)The time-displacement curve shows a relatively straight line.According to the equivalence force-Von mises diagram,it can be observed that when the external rotation exercise is done at 60°,the stress concentration of the glenoid is distributed in the lower part of the posterior glenoid.(3)When the external rotation is 90°,the stress concentration is distributed in the anterior and middle position of the lower part of the glenoid.2.According to the finite element model after surgery:(1)The postoperative model of the affected shoulder joint was abducted 60°: the inter-displacement curve of the humerus showed a relatively straight line.The bone detached from the glenoid margin when the humerus was externally rotated to 22.5°,indicating the internal fixation failed.(2)The postoperative model of the affected shoulder joint was abducted by 90°: the interdisplacement curve of the humerus showed a relatively straight line,and the internal fixation failed when the humerus was externally rotated to 31.5°.3.Stress analysis and remodel process of the glenoid after bone grafting:(1)The stress distribution of the transplanted bone fragments was concentrated in the "optimum circle" under the 2 working conditions of 60°and 90°abduction of the model after operation of the ipsilateral shoulder joint.(2)Based on the finite element model,within a certain range of external rotation,the bone graft had a small range of fretting displacement,and beyond the range of movement,the bone graft was unconstrained and the displacement increased significantly.(3)The patient’s imaging results showed that the bone block shaping process occurred concentratedly within 1 year after surgery,and the surface area of the graft showed a continuous downward trend from 3 months to 1 year after surgery,while the shape of the glenoid gradually stabilized after 1 year.The results of CT three-dimensional reconstruction showed that most of the graft absorption occurred outside the "optimum circle" of the glenoid,and the external absorption occurred along the edge of the "optimum circle".ConclusionIn this study,a finite element simulation modeling method for shoulder joint was proposed to verify the effectiveness of shoulder glenoid bone grafting surgery taken from the iliac bone in the treatment of shoulder joint anterior instability.The stable displacement changes of humerus in a specific range of motion can be observed by comparison with the unhealthy shoulder joint,and the effectiveness of iliac bone grafting can be confirmed by the degree of humeral stability,the change of glenoid concave and the occlusion effect of implanted bone blocks.The postoperative bone stress is mainly concentrated in the "optimal circle" of the glenoid,which suggests the bone shaping mechanism and predictable shaping results after autologous iliac bone grafting,which can provide biomechanical theoretical support and optimization plan reference for clinical practice. |
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