人體的脊椎由於具有許多功能如保護隱藏在內的脊椎神經，給予軀幹強力而柔軟的支撐，提供肌肉附著使身體可以動作平衡與制動等等，它在人類的日常活動中扮演著非常重要的角色。然而不正確的承受負荷、姿勢或者是長期個人職業上的擔負重物，許多症狀或下背痛就從如此的糟的工作環境而產生。脊椎的移動方式是如何影響正常的功能或者是不正確的姿勢或負荷模式怎樣的導致對脊椎的明顯的影響已引起研究者極大的注意。
有限元素法迄今已使用超過三十年，其中有些用來求解脊椎所遭遇的問題，建構的模型也隨著電腦科技和演算法的進步而發展，而且最近幾年在解決各種由簡化到複雜的問題上得到了新的進展。如我們所知的，有限元素法產生的結果當然和所解決問題的外型、選擇的材料性質、所描述的邊界和外力條件有關，即使其它條件在有限元素模擬執行時維持不變，當中的每一個要件的變化都會導致結果的不同。對早期年代的研究者想有一適當的模型來做脊椎更逼真的生物力學行為模擬來說，由於脊椎骨的後半部份元素的複雜不規則，常會造成一些麻煩。因此早期的研究學者通常會採用對稱的脊椎模型來簡化分析以及避免建構脊椎骨後部不規則形狀的困難。雖然在模型中這樣的對稱思想不致於造成錯誤的結果，不過它似乎也對我們想要的局部的結果造成實際狀態的朦朧不明,譬如在小面關節處的詳細的應力/應變分佈。
在我們的分析中，使用了三維幾何逼真的腰薦椎模型，它是由一連串在DICOM格式影像檔修正骨質輪廓再予以堆疊形成平滑的STL格式曲面檔案，且設定相關的外力和邊界條件所完成的可執行檔。我們期盼椎骨後部做了細微變化的處理後能幫助了解以前在簡單的外型考慮下沒有發現的細微改變。
這些有限元素模擬的結果顯示，非對稱的行為會隨著施加負荷的變大更加明顯。如此的現象吸引我們的興趣，去仔細審視嚴格假設非對稱性。從椎骨後半部非對稱性外型的考慮，以及這詳細的非對稱性外型，在施加負荷更大時，不管它分析考慮的是什麼事物，似乎都放大它的效應。因此這現象讓我們相信，如此非對稱行為的放大效應是來自於缺少將肌肉元素放在我們的模型中所致，如果我們採用如此細微的幾何模型然而不考慮來自於肌肉制動的平衡效應，在脊椎模型中的椎骨多處連接將引起中性穩定的問題。

The human spine plays an important role in the daily activity of the human beings for its multi-functions like the protection of the spinal cord housed within the spine, providing strong, yet flexible support for the trunk of the body, attachment of muscles for activation and balance of movement, etc. While the improper loading, postures or long-term weight-bearing in individual profession, many symptoms or low back pains arise from such bad work conditions. How the moving ways of the spine affect the normal functions or how the improper postures or loading modes result in evident effects on the spine have called much attention of the researchers.
Finite element methods have been widely used for latest 30 years to solve the encountered spinal disorders, the constructed models also developed with the computer technologies and algorithms, and got a novel progress in solving various problems from simple cases to complicated ones in recent years. As we know that the results of finite element methods intrinsically depend upon the geometry of solved problems, the selected material properties, boundary and loading conditions prescribed. Each of them would result in different situations, even if the other conditions were kept invariant during the performance of finite element simulations. The irregularity of the posterior elements of the vertebrae often causes some trouble for previous researchers to have an appropriate geometrical model to make a more realistic simulation on the biomechanical behavior of the spine. Therefore, the early researchers usually adopt a symmetric spinal model to simplify the analysis and avoid the difficulty of constructing the irregular shapes of the posterior parts of the vertebrae. Although such thought of symmetry in the model did not lead to wrong consequences, it seemed to keep some real status obscure when the local outcome was desired, for example, the detailed stress/strain distributions in the facet joints.
In our analysis a three-dimensional geometrically realistic model of the lumbosacral spine was built by a series of bony contour corrections on the digital imaging and communications in Medicine (DICOM) image files, and then stacking the contours to form a smooth stereolithography (STL) surface model, setting the corresponding loading and boundary conditions to accomplish the executable model. We expected that the treatments on the tiny change on the irregularity of the posterior parts of the vertebrae would help understand the detailed variations, which were not found before for simple considerations of the geometry.
Results of these finite element simulations showed that the asymmetric behavior would appear obviously, if the applied loads became larger. Such phenomenon attracted our interest to look over to hypothesize rigorously for the asymmetry. From the consideration of asymmetric geometrical representation of the posterior parts of the vertebrae, and this detailed asymmetric geometry seemed to amplify its effect if the loads were applied more larger, no matter what entities were analyzed. Thus the phenomenon made us believe that such amplifying effect on asymmetry behavior was resulting from lacking of the incorporation of the muscle elements in our model. The multi-connection of the vertebrae in the spine model will give rise to the neutral stability problem if the tiny geometry of the model was adopted while without considering the balance effect coming from the activation of muscles.

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