脊椎為支撐人體重量及運動的重要結構，由上至下可分為頸椎七節、胸椎十二節、腰椎五節、薦椎五節及尾椎骨。上下兩椎節間左右兩側有小面關節囊包覆連接，可用來抵抗扭矩及剪力。當椎節或小面關節先天不良或受傷而造成斷裂時，可能會使上下兩椎節分離。若左右兩側椎弓皆斷裂時，稱為椎弓解離，此時會造成患者的活動度降低。若是椎體再受重力作用而向前滑出，即是「脊椎滑脫症」，通常發生於第五腰椎及第一薦椎之間，且時常伴隨椎間盤退化的情形發生。

本文使用MSC.Patran作為有限元素前處理軟體，ABAQUS為後處理軟體，分析在腰薦角為40度時，第五腰椎及第一薦椎的滑脫情形，並細分為椎弓解離、一級滑脫、二級滑脫三種情況加以探討。治療方式為使用內固定系統配合PEEK與鈦材質的椎籠，分別固定第四腰椎至第一薦椎(打三節骨釘)以及第五腰椎至第一薦椎(打兩節骨釘)之間來分析討論，椎籠則統一植入第五腰椎第一薦椎間，並搭配四種運動情形(後仰、前彎、側彎、扭轉)來探討椎間盤、螺釘與椎籠的應力、應變能密度和端板相對轉角，希望能在脊椎病變治療上，提供更正確的治療方向。

本研究建立脊椎有限元素模型的步驟依次為，以電腦斷層掃描脊椎得DICOM影像檔，由醫學影像處理軟體3D-Doctor處理成STL平滑曲面檔，再以MSC.Patran修整模型的幾何外型、給定材料性質、設定邊界條件及施加負載後，生成有限元素實體模型，最後交由ABAQUS有限元素軟體求解。

The Spine is an important structure of the human body for supporting body weight and movement, from top to bottom, it can be divided into 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 sacral vertebrae and coccyx. The facet joints, which lie between upper and lower vertebrae, are located at both left and right sides of the posterior arch of the vertebra and can be used to resist torque and shear force. When the vertebrae or the facet joints suffered from congenital defects or injuries, it may lead to the separation of upper and lower adjacent vertebrae. When both sides of the posterior arch of the vertebra fractured, it is well known as” spondylolysis “ and usually causes patients to reduce their activities. If the injured vertebra subjected to gravity load to slide forward, it is called “spondylolisthesis”, usually occurring at L5-S1 level, and accompanies with the diseases of disc degeneration.

This study used MSC.Patran as the pre-processing tool and ABAQUS as finite element program solver to analyze the slippage between the fifth lumbar vertebra L5 and the sacrum S1 with the lumbosacral angle 40 degrees under three cases: spondylolysis, grade 1 and grade 2 of spondylolisthesis. The ways to treat the above cases were uses of the internal fixation systems, 2 or 3 segments, PEEK or titanium material of the cage, and both L4-S1 and L5-S1 levels were analyzed and discussed. The cage was inserted at L5-S1 level and four movements like extension, flexion, lateral bending and axial rotation were considered. This study explored the maximum von Mises stress, strain energy density, distributing among the intervertebral discs, screws and vertebral cage, and relative rotation angle of the endplates, and hoped that this investigation would provide more accurate treatment of spinal diseases.
This study established an finite element model of the lumbosacral spine by a series of processing steps as follows: getting the DICOM images from the CT scan, handling by the medical image processing software 3D-Doctor to obtain a smooth surface STL format profile, trimming model on the geometry, setting material properties, boundary conditions and the loads in MSC.Patran, and then creating an executable finite element model, and finally, putting this model into ABAQUS for solving.

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