有限單元法應用於多項肩關節手術之應力分析

Stress Analysis in Various Shoulder Surgeries by Finite Element Method

楊卿潔(Ching-Chieh Yang)

指導教授 ： 陳榮順 ； 葉孟考

國立清華大學/工學院/動力機械工程學系/博士(2013年)

摘要

有限單元法(Finite Element Method)是用數值分析的方法來研究物理學領域相關問題的一門學術。有限單元法在醫學及骨科之臨床應用相當廣泛，可以預見的，有限單元法將持續的對骨材之設計研發多所貢獻。下列章節將針對有限單元法應用於多項肩關節手術及反置型人工肩關節設計之應力分析詳為論述。
肩關節係由三個解剖次關節：肩肱關節(Gleno-Humeral Joint)，肩鎖關節(Acromio-Clavicular Joint)，胸鎖關節(Sterno-Clavicular Joint)以及兩個關節空間：肩峰下空間(Subacromion Space)及肩胸空間(Scapulo-Thoracic Space)，外加一個懸吊機轉：喙鎖機轉(Coraco-Clavicular Mechanism)所構成。論文之解剖文獻回顧僅針對肩鎖關節手術及反置型人工肩關節手術相關之解剖結構行之。對肩關節結構之詳細解剖知識有助於肩關節之建模及手術之應力分析。
雖然肩關節手術於近數十年有長足之進步，肩鎖關節手術，肩關節外傷之後遺症，無法修補之旋轉肌破裂對骨科醫師而言仍為鉅大之挑戰。以目前所知，本論文為首篇肩鎖關節之有限單元法相關文獻，二維有限單元之模型係根據臨床X光檢查統計所得之骨骼結構平均參數及文獻所得之組織材料參數建構而成。建模之過程係採用有限單元分析(Finite Element Analysis)商業軟體ANSYS。分析之過程依序為：前處理，求解，以及後處理。在前處理之步驟，選擇適切之單元類別為首要之務，再則輸入組織之材料參數，繼而建模及畫分網格；在求解的過程則給予適當之邊界條件及負載；求解後進入後處理階段，可以得到應力、位移之分佈圖。文中所建為二維之模型，所選擇之單元為Plane 42。
為進行反置型人工肩關節相關之研究，文中根據法國Tornier公司所生產之反置型人工肩關節建模，模擬實驗顯示肩盂球之偏心設計及外側加厚設計，雖可減少肩胛鑿痕(scapular notching) ，但相對的要付出肩盂基板（baseplate）應力集中以及後續肩盂基板鬆脫的代價，最大應力出現在下方螺絲之基部，顯示下方螺絲中間部位之斷裂原因可能是直接撞擊造成。本研究係提供另一可行之工具以為反置型人工肩關節肩盂部份(glenoid component)之設計，爾後應用反置型人工肩關節之模型再行研究，可探討反置型人工肩關節肱骨部份(humeral component)之最佳設計，亦可探討在諸多不同肱骨部份暨肩盂部份設計中之最佳化組合。

關鍵字

有限單元法 ； 肩胛鑿痕 ； 肩盂基板 ； 關節肩盂部份

並列摘要

The finite element method (FEM) is a numerical method to solve the fields problems. FEM has been used in several fields of medical practice and orthopedic practice. It is acknowledged today that FEM will, continuously, contribute to further progress in the design and development of orthopedic implants. In the thesis, we implemented the FEM model to analyze the stress distribution in various shoulder surgeries and investigate the stress distribution in various glenoid designs of reversed shoulder prosthesis (RSP).
The shoulder joint is composed of three anatomic components: gleno-humeral (G-H) joint, acromio-clavicular (AC) joint, sterno-clavicular (SC) joint and two main space, namely, the subacromion (SA) space, the scapula-thoracic (ST) space and the coraco-clavicular (C-C) mechanism. Since the author focus on the application of finite element analysis on the realm of shoulder surgery, the anatomic review is emphasized on the detailed structures which are more correlated with surgery of acromio-clavicular joint and design of RSP. With detailed anatomy knowledge, we can construct the finite element model for stress analysis of shoulder surgery.
Despite of the tremendous progress for shoulder surgery in decades, the surgery for AC joint reconstruction, sequelae of trauma and un-reparable rotator cuff tear remained challenging task for orthopedic surgeon. To our knowledge, this is the first FEA study on AC joint complex. The two dimensional (2D) finite element (FE) models are constructed according to clinically obtained radiographic data and documented parameters of tissues material properties. ANSYS commercial software was adopted to complete the construction process based on finite element method (FEM). The analysis process in commercial software ANSYS are pre-processor, solver, and post-processor orderly. In pre-processor, choice of proper element type is the first step, followed by entering the material properties of structure. Then, contribute the geometry model and mesh model. In solver, after giving proper boundary conditions, load and solve the problems. As for post-processor, the data and figure could be obtained from the deformation and stress results. In this research, the models are 2D, the element Plane 42 was used.
The AC joint Model was then verified by comparing with the published experimental results. The first simulated results showed that coraco-acromial ligament (CAL) plays significant role in biomechanical function of AC joint, and also pointed the numerical support for existence of Salter’s complex. Subsequent studies with this model, we further confirmed that arthroscopic subacromion decompression (ASD) may insult the Salter’s complex and lead to post-operative complication of AC joint. Finally we applied the AC model to simulate distal clavicle resection (DCR). We dictated that the direct method is a better method for DCR and the proper length of DCR is found to be between 0.6 and 0.7 cm.
For the study of RSP design, we constructed a model of RSP which is based on the product of Tornier’s company. Simulated results dictated that increased eccentric offset and lateral offset of glenosphere, although being able to reduce scapular notching, may pay the penalty of significant stress concentration over glenoid and its subsequent loosening. Maximum stress occurs at the base of inferior screw elucidates the direct contact failure mode at the middle of inferior screw. Our study provides an alternative tool for the optimal design of glenoid component of RSP. We may further implement the RSP model to find the optimal humeral design and optimal combinations of various designs of RSP in the future.

並列關鍵字

Finite Element Method ； scapular notching ； baseplate ； glenoid component

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