臺灣博碩士論文加值系統

骨盆環由兩塊髖骨及一塊薦骨所組成，其中薦骨作為脊椎的基石及骨盆環核心所在，為人體生物力學穩定的重要關鍵。在臨床上骨盆環骨折分為三種類型(Type A、B、C)，其中以第三類型骨折Type C最為嚴重，骨盆環前環及後環皆為不穩定骨折狀態，而本研究所探討的薦骨垂直性骨折(Denis fracture type)則會發生於Type C的狀況，此種狀況通常會發生於骨盆環受到劇烈撞擊的事故，如車禍、跌倒等…。
臨床對於骨盆環骨折治療的目標，主要為重建骨盆環穩定性，使骨盆環與上肢及下肢維持正常的力學傳導，但是目前臨床上缺乏對於骨板、骨螺絲固定位置上穩定性差異的評估。本研究係結合三維有限元素分析法，對於臨床上薦骨垂直性骨折手術所使用的骨板、骨螺絲及其固定位置，以手術上所使用的方式來建立骨盆環薦骨骨折模型，並建立韌帶、邊界條件和施力條件，藉由三維有限元素分析法來探討完整骨盆環及骨折骨盆環之生物力學特性。
有限元素分析法對完整骨盆環所分析出來的結果與使用人類大體骨盆環所做的實驗相比，完整骨盆環薦骨部位的位移趨勢與使用材料試驗機(MTS)來壓大體骨盆環薦骨部位的趨勢呈現相近的結果。目前臨床上骨盆環薦骨垂直性骨折較為通常的治療作法是使用骨板固定於薦骨S1的位置，但因為這樣的作法會造成病患有明顯的異物感於體內，所以本研究將骨板固定位置移至薦骨S2，此作法在臨床上已經有幾個案例，且治療效果不錯但仍缺乏穩定性評估。有限元素分析骨盆環薦骨骨折的情況，研究所建立的模型都是使用互鎖式骨板，骨板在兩種不同的固定位置，薦骨垂直骨折有三種型態Denis I、II、III，就骨折面受力後產生的滑移與空隙皆小於2mm，而骨折模型上所使用的骨板為鈦合金材質，在應力集中的最大應力皆小於鈦合金可承受的閾值，骨螺絲與骨頭間的摩擦力也都低於傳統位置所產生的摩擦力，可推測骨螺絲鬆脫風險較低，由結果可得出若將骨板置於薦骨S2的位置是可以作為手術時的另一個選擇。

Summary
The aim of this study is to investigate the biomechanical influence of fixation location, S1 and S2 levels, in posterior tension band plate fixation for pelvic ring fracture. The general location for the plate to fixed is at S1 level which would irritation and make the patient uncomfortable. This study investigates the biomechanical effect of the plate fixed at S2 level in order to reduce the irritation feeling. The finite element analysis is employed to simulate the pelvic ring with intact model and three types of fracture pelvic models. The results showed that, S2 level plate fixation offers a similar biomechanical response, in terms of displacement and stress distributions, comparing with S1 level fixation, but the structure of S2 fixation is more stable than S1 fixation. Both S1 and S2 level fixations possess acceptable healing indices, fracture surface sliding and gap, while S2 fixation is better than S1 fixation. Both S1 and S2 level fixation possess high safety factor in terms of plate and screw stress while S2 fixation is again better than S1 fixation. Friction force assessments on the interface of bone screw indicated that S2 level fixation has less risk in screw loosing. The biomechanical results in osteoporosis models displayed similar outcomes in all the above indices, i.e., S2 level fixation is better than S1. To conclude: Although S1 level fixation is adopted clinically in most pelvic ring fracture treatment, S2 level fixation might provide better mechanical advantages in addition to its superior patient subjective feeling.
Key words: Pelvic ring fracture, Posterior tension band plate, Biomechanical evaluation
INTRODUCTION
Clinically, using compression plate to fix posterior pelvic ring possesses a high success rate, except for osteoporosis patients. In general, the plate will be secured at the S1 level. This level however would induce significant uncomfortable for patient due to plate protrusion. Studies have been proposed to solve these problems. For example, grooves on the bilateral ilium and sacrum spinal are created with a chisel to decrease the plate protruding[1]. However the induce of grooves would increase the unnecessary damage to the ilium and sacrum. Using locking plate with small plate is another way to provide a solution[2]. However, in order to precisely position the screw, excessive soft tissue dissection is required which increase the infection risk comparing to the percutaneous screwing in traditional plate. This study proposed a simple and easy improving by secure the plate at S2 level, instead of S1 level, to reduce the patient discomfort. The objective of this study is to evaluate the biomechanical influence of this S2 level approach. The specific aims includes: (1) To evaluate the difference, biomechanically, between S1 level secure and S2 level secure; (2) To confirm the S2 level secure is not inferior than S1 level secure; (3) To evaluate whether S2 level secure can works on osteoporosis patient.

MATERIALS AND METHODS
Finite Element models
The pelvic ring computed tomography images from visible human project [3] were imported to Mimics, segmentation and modeling software to build the pelvic ring. The STL files, outputted from mimics, were input to Geomagic, modeling software, to smooth the pelvic model as well as converting from surface model to solid model. Cortex of bone was then generated by shrinkage the original solid pelvic model 1 mm inward. Finally, Solidworks, another modeling software, was employed to create the cartilage and L5 in the pelvic model. In addition to the intact model, three fracture models, different fracture sites as described below, as well as virtually implant the bone plate and bone screws to these fracture models were also carried in Solidworks. Finite element analyses were carried within ANSYS software. Spring elements were used in ANSYS to simulate the tension resistant ligaments.
Material properties
All material properties in this study are assumed to be homogenous, isotropic and linear elastic. The simulated model includes L5, sacrum, pubic symphysis cartilage, and the entire pelvis with cortical bone and cancellous bone structures. Table 2.1 listed the mechanical properties of the normal as well as the osteoporosis cortex and cancellous bones[4, 5](TABLE PAGE 21). The plate, simulated as titanium, was assigned with a Young’s modulus of 114000 Mpa and a Poisson’s ratio 0.3.
Ligaments around the pelvic ring were simulated with spring element and only the major ligaments were considered which included: ASL, PSL, ISL, ST, and SS. According to the experimental study, which obtain the ligaments stiffness by in-vitro tension test[6-9], Table 2.2 listed the spring constants of each ligament structure(TABLE PAGE 22). It is noteworthy that the spring constant is equally distributed to individual spring forming each ligament.
Boundary conditions
In order to verify with existing experiment[10], vertical loading of 1000N was applied on top of L5 in intact pelvic ring model to meet the loading conditions of the experiment. Model was fixed at both sides of the acetabular fossa. The interface of sacroiliac joint was set to be frictionless while the pubic symphysis was set to be bonded. For the fracture simulation, three fracture types, representing Denis I, II, and III respectively, were generated with vertical fracture at different positions of left sacrum (FIGURE PAGE 24) and a friction coefficient of 0.3 was assigned to the fracture interface. Moreover, SS and ST ligaments on the left side, fracture half, of the pelvic ring were removed. The interface between plate and screws was set to be bonded to simulate the locking plate while interface between screw and bone was set to with friction coefficient 0.4 to investigate the loosing risk. Then 600N, instead of 1000N to simulate the upper body weight, was applied as the loading on fracture models.

RESULT AND DISCUSSION
For the intact validation, the load-displacement curves of the finite element result and experimental outcome were similar both in slope and values. For both S1 and S2 level fixation, the peak stress all occurred in screw regardless of the fracture type, and the highest stress arose in Denis III with S2 is safer than S1. (The safety factors are greater than 5 in most models.) For healing evaluations, the fracture interface sliding distance and gap opening in S2 level fixation are all less than those of corresponding S1 level fixation. The maximum interface gap opening occurred in Denis III fracture. This could due to fact that Denis III fracture possesses the longest fracture length and the maximum opening always occurred at the fracture tip. Unexpectedly, the maximum sliding distance occurred in Denis I fracture which possesses the shortest fracture length. This might due to the fact that fracture surface of Denis I suffered a larger moment with its longer level arm from the L5 loading site. Due to the fact that the threads were missing in the screw model, replaced by cylinder with large friction, the frictional force between the screw and bone is employed to evaluate the screw pullout risk. The results showed that S2 level fixation, in a relative sense, has less risk in screw loosing. However, it is noted that in this study the interface between plate and screw are boned to simulate a locking plate, this screw loosing assessment might not be that significant. Finally, in osteoporosis condition, all indices displayed identical outcomes as in normal bone condition, i.e., S2 level fixation is not inferior than the fixation at S1 level.

CONCLUSION
In this study, the finite element analysis is used to analyze the biomechanical effect of S1 and S2 level plate fixation. Five conclusions are given:
(1) S2 level plate fixation offers a similar biomechanical response, in terms of displacement and stress distributions, comparing with S1 level fixation, but the structure of S2 fixation is more stable than S1 fixation.
(2) Both S1 and S2 level fixations possess acceptable healing indices, fracture surface sliding and gap, while S2 fixation is better than S1 fixation.
(3) Both S1 and S2 level fixation possess high safety factor in terms of plate and screw stress while S2 fixation is again better than S1 fixation.
(4) Friction force assessment on the interface of bone and screw indicates that S2 level fixation has less risk in screw loosing.
(5) The biomechanical results in osteoporosis condition display similar outcomes in all the valuated indices, that is S2 level fixation is better than S1.
Although S1 level fixation is adopted clinically in most pelvic ring fracture treatment, S2 level fixation may provide better mechanical advantages in addition to its superior patient subjective feeling.

中文摘要 I
Extended Abstract II
誌謝 VII
目錄 VIII
表目錄 X
圖目錄 XI
第一章 緒論 1
1.1 前言 1
1.2 骨盆環解剖構造 2
1.3 典型骨盆環骨折及垂直性薦骨骨折 5
1.4 臨床治療方式 7
1.5 有限元素分析法 9
1.6 文獻回顧 11
1.6.1 骨盆環韌帶和身體重力對骨盆環整體穩定度之影響 11
1.6.2 骨盆環最大受力方式(薦骨垂直受力) 11
1.6.3 Type C不穩定骨盆環有限元素分析之相關模擬 12
1.7 研究動機與目的 13
第二章 材料與方法 15
2.1 研究流程 15
2.2 三維骨盆環有限元素模型之建立 17
2.2.1 三維骨盆環幾何模型之建立 17
2.2.2 三維骨盆環材料參數之建立 21
2.2.3 三維骨盆環網格化 23
2.2.4 骨盆環有限元素模型之負載及邊界條件 24
第三章 結果 25
3.1骨盆環合理性分析 25
3.1.1 薦骨受力後移動方式 25
3.1.2 薦骨受力後彈簧所承受之張力 27
3.1.3 薦骨受力後與兩側髖骨的作用力 29
3.2 有限元素模型與大體實驗之驗證 30
3.3骨折骨盆環模型與正常模型之驗證 31
3.4 S1 level與S2 level之應力分布 32
3.5 薦骨垂直性骨折處之斷面滑移量與空隙 34
3.6 骨螺絲與骨頭間之摩擦力 36
第四章 討論 37
4.1 臨床治療方式探討 37
4.2 骨盆環骨折斷面接觸條件比較 38
4.3 骨板之等效應力分布 40
4.4 薦骨垂直性骨折癒合指標探討 41
4.4.1 薦骨垂直性骨折處之斷面滑移量探討 41
4.4.2 薦骨垂直性骨折處之斷面空隙探討 42
4.4.3 骨板固定位置之影響 43
4.5 骨板骨螺絲鬆脫探討 44
4.6 本研究之限制 45
第五章 結論 46
參考文獻 47

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