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論文名稱(外文):Acetabular Cup Intra-operative Stability: Bending Measurement
指導教授(外文):Chih-Han Chang
外文關鍵詞:bending moment measurementacetabular cupinitial stabilityfinite element analysis
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全人工髖關節置換手術是骨科常見之重要手術,而術後置換物的鬆脫是造成置換失敗較常見的原因。Press-fit 是臨床上常使用的髖臼置換物固定方式,在骨質良好的情況下,此方式在不外加其他螺絲固定時有較佳的穩定度。置入物與骨質間的微小位移量常因不當的置入與承受高附載活動下而產生,固定方式不良也會造成骨質與置入物表面成長不佳,這將導致術後髖臼杯鬆脫的情況產生。
由實驗結果得到,2mm press-fit尺寸下髖臼杯臨界彎矩值為19~21Nm,實驗結果顯示隨著cup尺寸增加,其臨界鬆脫值可能因接觸面積變大,磨擦力增強之關係而隨之增加;而微小位移量的部分則隨尺寸增加而減少,可視為在同樣壓接尺寸下較大的髖臼杯有較佳之穩定度。本研究測量出在醫師操作下2mm press-fit可承受10~15彎矩且產生小於0.18mm位移量之髖臼杯可視為穩定,而由模擬的結果得到1mm press-fit 的髖臼杯在同樣受力條件下,髖臼杯產生的位移量較2mm press-fit固定程度之髖臼杯大於40%,在實際情況下若由臨床醫師判斷此1mm press-fit髖臼杯可能為不穩定。在實驗結果部分得到測量儀之變形量對量測彎矩是準確的,本測量儀可讓醫師於術中量測之彎矩即時評估所放置之cup在人體內是否處於穩定狀態,並可有效評估單一臨床醫師操作下其感受穩定之彎矩值,基於本實驗的結果得到髖臼杯在承受10~15Nm且不產生過大的位移量時即可判斷為穩定狀態。

Aseptic loosening is one of the most common complications of total hip arthroplasty, an important and common orthopedic surgery. Press-fit is a clinical option to secure the acetabular component in acetabulum. This approach is possible to provide sufficient initial stability without using screws. Initial stability is essential for bone ingrowth. Without sufficient initial stability, large relative micro-motion may occur between the cup and the pelvis under dynamic loading. This could reduce the bone ingrowth onto the cup exterior surface thus prohibit the osseous integration and eventually leads to the cup loosen and failure.
At current stage, there was no quantified method to access the stability of a press-fitted cup during surgery other than the surgeon’s subjective judgment. The purpose of this research was to design and evaluate a simple and workable device, bending moment measurer, for cup stability access during surgery. Both in-vitro experiment and finite element analysis (FEA) were employed to perform the initial stability evaluation. In the experiment, the bending measurement of the press-fitted cup was perform by orthopedic surgeon with the developed device and compared the measurement with material testing system (MTS). In addition, three dimensional finite element models, validated by the experimental outcomes, were also generated to further evaluate the device.
From the experiment, a 2mm press-fit cup’s critical loosening moment, 19~21Nm, increased as the cup size, 48mm~52mm in diameter, increased, possibly due to the frictional force increasing from enlarged contact area. Also, under the same bending moment, the cup displacement increased as the cup size decreased. Quantitatively, the surgeon justified a stable cup when the cup was capable to withstand 10~15 Nm of bending moment with displacement less than 0.18mm. From FEA it couls be identified that under-reamed 1mm of press-fit, the displacement of the cup could enlarge by 40% which might be justified by the surgeon as unstable. The present study showed that: with the bending moment measurement device, a surgeon could evaluate the stability of an acetabular component by using the intra-operative bending measurement. This developed device can accurately measure the applied bending moment on cup. Based on the in-vitro experiment a cup capable to bear 10~15 Nm of bending without showing too much displacement was justified as stable cup.

Abstract I
中文摘要 III
誌謝 V
Chapter 1. General Introduction 1
1.1 Background 1
1.1.1 Hip Joint 1
1.1.2 Total Hip Replacement 3
1.2 Literature Reviews 8
1.2.1 Relationship between the Initial Stability and Bone Ingrowth 8
1.2.2 The Ideal Ream Size of Press-fit Fixation 8
1.2.3 Finite Element Analysis 10
1.3 Motivation and Goal 11
Chapter 2. Materials and Methods 12
2.1 The Research Process 12
2.2 Pilot Prototype Design 14
2.3 Measurement Validation 15
2.4 Experiment Setups 17
2.5 Finite Element Analysis of Bending Measurement 22
2.5.1 Modeling of Measurement 22
2.5.2 Modeling of Acetabular Cup and Saw bone 23
2.6 Loading Conditions and Boundary Conditions 24
2.6.1 Validate Simulation Model of Bending Measurement 24
2.6.2 Simulation of Acetabular Cup Stability 25
Chapter 3. Results 27
3.1 Extensor-meter Validation 27
3.2 Experiment by Surgeon 28
3.3 Experiment by MTS 29
3.4 Simulation by Finite Element Analysis 31
3.4.1 Validate Simulation Model of Bending Measurement 31
3.4.2 Von-mises Stress Comparison 32
3.4.3 Simulation of Acetabular Cup Stability 33
Chapter 4. Discussion 35
4.1 Factors Affecting Experiment Results 35
4.2 Effect of Cup Size on Initial Stability 37
4.3 Factors Affecting Simulation Results 37
4.4 Unstable Acetabular Cup 38
4.5 Limitations of Bending Measurement 39
Chapter5. Conclusion and Future Work 40
5.1 Conclusion 40
5.2 Future Work 41
Reference 42
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