臺灣博碩士論文加值系統

近三十年來，脊椎融合手術結合脊椎內固定器已廣泛應用於脊椎的治療。且後側方骨融合術及後方骨融合術可以有效治療脊椎不穩定的問題。但是由於植入補骨和脊椎內固定器使得腰椎生物力學行為遭受改變，因此在臨床報告中，發現部份臨床病例出現鄰近端椎間盤加速退化、小面關節過度增生、後側方骨融合後椎足斷裂、後方骨融合後椎弓斷裂等併發症，甚至也有椎足螺釘斷裂而引發背痛的情形。因此本研究的目的即探討這些晚期併發病的臨床問題，故以有限元素法來探討這兩種骨融合術的生物力學變化，並且蒐集斷裂脊椎內固定器和臨床資料，且採用電子顯微鏡觀察斷裂面以了解脊椎內固定器破壞機轉。
本研究是以ANSYS 5.5軟體建立三度空間五節腰椎有限元素模型，並在L3-4的運動肢段植入脊椎內固定器及補骨元素進行生物力學分析。施加負荷是在150 N的垂直力作用下，個別施加10 N-m的前彎、後彎、側彎及扭轉的力矩於L1椎體上，並固定L5椎體下方。而所有腰椎融合模型分成五組，分別為正常腰椎模型、後側方骨融合模型、後方骨融合模型、後側方骨融合加脊椎內固定器模型、後方骨融合加脊椎內固定器模型。
關於脊椎內固器的斷裂問題，本研究是蒐集16位脊椎內固定器斷裂病人的病例資料，包括記錄骨融合狀態、椎足螺釘斷裂時間及位置。並且以電子顯微鏡放大斷裂面以觀察破壞情形。在生物力學方面，則建立四組二度空間有限元素模型探討固定界面的問題，其模擬狀態包括螺紋停在固定界面處，多一節螺紋埋入固定界面處，多一節螺紋露在固定界面外，螺紋與骨的固定界面不完全接合。
本有限元素模型計算出椎足的最大應力在後側方骨融合後是2.35倍大於正常腰椎模型，且是發生在側彎狀態。而椎弓的最大應力在後方骨融合後其增量是1.78倍大於正常腰椎模型，且也是發生於側彎狀態。但一旦加入脊椎內固定器之後，則兩個骨融合術與正常腰椎比較下，其椎足和椎弓的的最大應力差異量有減少的趨勢，但仍維持較高的應力。
而鄰近骨融合上端椎間盤的應力，最大增量達17%，發生在扭轉狀態；鄰近骨融合上端小面關節的接觸力，最大增量達10%，發生在側彎狀態。臨床病例分析結果指出椎足螺釘斷裂發生在下方有12人，斷裂在上方位置有4人。而斷裂在上方的特徵，骨折型態病患包括3位，其特徵是斷裂面除了疲勞條紋外，周圍有撕裂的痕跡，螺釘斷在較深螺紋位置；斷裂在下方的特徵大都是脊椎滑脫的病患，其椎足螺釘斷裂面平整，且斷面大都呈現疲勞紋，椎足螺釘也都斷在第一節螺紋。而四組二度空間模型計算結果指出椎足螺釘受力最大皆發生在固定界面，且螺釘螺紋露在骨界面外，則會增加應力集中效應。
本研究結論指出後側方骨融合後卻發生椎足斷裂的病人，和後方骨融合後發生椎弓斷裂的病人，其原因是骨融合後應力集中效應所引起。鄰近椎間盤及小面關節的確會在骨融合後造成其應力及接觸力的增加。而關於椎足螺釘的斷裂，本研究發現椎足螺釘斷裂在上面是由於病人脊椎前方支撐不足而斷裂，故斷裂時間較短。而椎足螺釘斷裂在下方是發生在脊椎前方有足夠的支撐力作用下，但因大部分的受力都在下端螺釘而造成斷裂，且病患補骨已融合，故斷裂時間較長。但不論是何種型態的破壞，根據疲勞紋路方向，椎足螺釘的破壞力量是來自腰椎的前彎力矩或自重。

During the last 30 years, spinal fusion with spinal instrumentation has been widely used in the spinal treatment. Posterior fusion and posterolateral fusion can effectively manage spinal instability. However, the biomechanical behavior of lumbar spine was altered because of implantation of bone graft or spinal instrumentation. In clinical reports, some clinical cases presented in accelerated degeneration of adjacent disc, hypertrophy of facet joint, pedicle fracture after posterolateral fusion, and spondylolysis acqusita after posterior fusion. Furthermore, the breakage of pedicle screw induced back pain symptom of patients. Therefore, this study was aimed to investigate these clinical problems about late complication. Finite element analysis was conducted to study the biomechanical alteration in posterior fusion and posterolateral fusion. The collection of broken screws and clinical data, and observation of fracture surface using scanning electron microscope were applied to study mechanism of screw breakage.
Three-dimensional nonlinear finite element model (FEM) of the lumbar spine were established using ANSYS 5.5 commercial package. The L3-4 motion segment was chosen to implant spinal instrumentation and bone graft for biomechanics analysis. The 10 N-m flexion, extension, axial rotation, and lateral bending with pre-load 150 N were imposed on the L1, respectively. The boundary conditions were to fix the degree of freedom of bottom nodes in the L5 vertebral body. A total of five finite element models were constructed, including intact spine model, posterior fusion model, posterolateral fusion model, posterior fusion with implant model, and posterolateral fusion with implant model.
Regarding the breakage of pedicle screw, sixteen patients were enrolled in clinical retrieval analysis. The failure time, failure site and fusion status were recorded. The cross section area of failure screws was magnified to observe by scanning electron microscope. In biomechanical analysis, four two-dimensional finite element models of pedicle screw fixation were constructed to investigate the four problems about the fixation interface, included the thread end was stopped at the fixation junction, the thread end was above the fixation junction for one thread, the thread end was below the fixation junction for one thread, and an incomplete connection between bone and screw due to micro-movement of pedicle screw.
The FEM calculated that pedicle in posterolateral fusion was maximally 2.35 times larger than that in intact lumbar spine in lateral bending. The pars interarticularies in posterior fusion was maximally 1.78 times larger than that in intact lumbar spine in lateral bending. However, when the two fusion models added spinal instrumentation, the difference in stress of pars interarticularies and pedicle between posterior fusion and posterolateral fusion tended to moderate. But the high stress still remained in pars interarticularis of posterolateral fusion and pedicle of posterior fusion. In the stress of adjacent disc, the maximum increase reached 17% in torsion. In the contact force of facet joint, the maximum increase reached 10% in lateral bending mode. In clinical retrieval analysis, the screw broke at cephalic site has four patients, included three patients with spinal fracture. The characteristics of fracture surface revealed tensile fracture, fatigue striations and fracture site inside the bone. The screw broken at caudal site has twelve patients, included eleven patients with spondylolisthesis. The characteristics of broken screw displayed most fatigue striations and fractured at the first thread. The four two-dimensional finite element models estimated the pedicle screw had maximum stress at fixation junction, and also indicated that stress concentration was enhanced when threads were outside the fixation junction.
The conclusion of this study indicated that the pedicle fracture after posterolateral fusion and pars interarticularies fracture after posterior fusion were because of effect of stress shielding. Besides, this study also indicated that stress of adjacent disc and contact force of facet joint did increase after the patients conducted fusion procedures. Regarding the screw breakage, this study found the patients with insufficient anterior support such as spinal fracture had broken screws at cephalic site within a short time. The patients with sufficient anterior support had broken screws at caudal site in a long time, because most of the loads shared on distal screws. Additionally, these patients usually had solid fusion. Whatever the types of screw breakage, the force about screw failure was from flexion moment or self-weight in accordance with directions of fatigue striations.

封面
中文摘要
英文摘要
目錄
表目錄
圖目錄
第一章、前言
1-1　脊椎的解剖及生理
1-1-1　椎體的生物力學特性
1-1-2　椎間盤之生物力學特性
1-1-3　小面關節之生物力學特性
1-1-4　韌帶之生動力學特性
1-2　脊椎的病變及處理方式
1-3　脊椎內固定器簡介
1-4　腰椎融合手術的臨床問題
1-5　有限元素法的文獻回顧
1-6　研究動機與目的
第二章、材料與方法
2-1　有限元素分析
2-1-1　正常腰椎有限元素模型
2-1-2　後側方骨融合模型
2-1-3　後方骨融合模型
2-2　脊椎內固定器的斷裂分析
第三章、結果
3-1　腰椎元件受力分析結果
3-1-1　骨融合的運動範圍
3-1-2　鄰近椎間盤及小面關節
3-1-3　L3椎足的應力分析
3-1-4　L3椎弓的應力分析
3-1-5　補骨的應力和黃韌帶的受力
3-1-6　椎體L3及L4的應力
3-1-7　椎間盤L3-4的應力
3-2　脊椎內固定器斷裂分析結果
第四章、討論
4-1　有限元素模型基本假設及可能造成誤差的來源
4-1-1　腰椎有限元素模型的基本假設
4-1-2　未君肌群的假設
4-1-3　骨融合模型的假設
4-1-4　負荷條件的探討
4-2　臨床取出物分析之限制
4-3　研究結果的討論
4-3-1　骨融合的有限元素探討
4-3-2　脊椎內固定器破壞分析的探討
第五章、結論
第六章、未來研究方向
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