臺灣博碩士論文加值系統

全人工髖關節置換目前已廣泛應用於骨科手術中。而其中髖臼杯鬆脫為無骨水泥固定式髖臼杯組件中最常見的術後失敗原因之一。髖臼杯鬆脫主要是因為臼杯植入髖臼窩後初期的不穩定所造成。此微小的相對位移量會阻礙骨質完整長入髖臼杯表面的能力，而導致日後臼杯鬆脫。一般來說使用半球型髖臼杯配合數根骨螺絲為最常採用的固定方式之一。然而目前對於使用骨螺絲固定髖臼杯組件的力學機轉仍不十分清楚，並且髖臼杯的初期穩定度同樣會受到骨盆強度及臼杯表面摩擦係數所影響。

本研究利用電腦斷層掃瞄影像資料建立三維骨盆及髖臼杯組件之有限元素模型，利用此電腦模型來探討鎖入骨螺絲之數目及位置、骨盆骨質強度、和髖臼杯表面摩擦係數對臼杯穩定度之影響。模擬結果發現鎖入的骨螺絲只能提供螺絲附近較高的穩定性，因此在局部的區域內鎖入多支的骨螺絲對臼杯穩定度幫助不大。並且建議醫師鎖入數隻分散的骨螺絲即可提供較大的穩定面積。另外臼杯穩定度會隨著骨質強度的衰減呈現非線性的減少，因此在骨質較差的病人建議額外多鎖入數根骨螺絲來提高臼杯的穩定度。並且發現保留軟骨下骨層能提供顯著的固定能力。模擬結果顯示髖臼杯表面摩擦係數同樣會對臼杯穩定度有明顯的影響，建議醫師選用高摩擦係數的臼杯來提高髖臼杯的穩定度。

增加螺絲數目理論上可提高髖臼杯穩定度，但鎖入偏心骨螺絲卻可能減低固定效果。本研究將髖臼杯以1mm 壓配法植入人造骨盆中，來探討鎖入1 mm offset的偏心骨螺絲及鎖入15o和25o的angular偏心骨螺絲對臼杯穩定度的影響。實驗結果發現當鎖入螺絲時只有15o angular的偏心時候，並不會對臼杯穩定度造成顯著的影響，但當偏心角度達到25o或是1 mm offset的偏心螺絲時，會明顯地降低應有的固定能力。因此臨床醫師在鎖入螺絲時，必須注意鎖入的角度及位置與否正確，否則增加螺絲的數目沒辦法提供髖臼杯額外的穩定度，反而會降低固定效果。

除了臼杯鬆拖，髖球頭脫臼也是另外常見的術後後遺症之一。髖球頭脫臼主要是因為臼杯植入的角入不正確所造成，一般來說臼杯是以abduction 45o，anteversion 15o的角度植入髖臼窩中。但是對於年輕或經驗不足的醫師要將臼杯以最佳的角度植入髖臼窩中，並不是容易的事情。目前雖然有多種電腦輔助手術系統來幫助醫師植入髖臼杯，但因為此些系統價格昂貴或操作過於複雜而降低臨床使用率。本研究提出以單一影像進行空間座標定位之理論，並應用此理論研發出電腦導引髖臼杯植入之系統：CupNav system。目前實驗室校正得到理論誤差小於0.05%，系統誤差小於2o，雖然仍有許多困難及問題有待克服解決，不過本系統證明可利用最少的硬體資源及經費將電腦輔助手術應用於髖臼杯植入手術之可行性。

Total hip replacement (THR) is a common surgical procedure in orthopedics. One of the major failure modes of THR is the loosening of the cementless acetabular cup. Insufficient initial fixation results in increased micromotion between the cup and pelvis under dynamic loading, which prevents bone ingrowth and eventually causes loosening. Screws are widely used to enhance the initial stability of the acetabular cup, especially when a hemispherical cup with a porous coating is used. However, the biomechanical effects of screw fixation on the initial stability have not been thoroughly evaluated. In addition, the cup stability would be affected by the pelvic bone stiffness, the friction force, and the presence of screw eccentricity. The objective of this study was to investigate the effects of screw configurations, pelvic bone stiffness, and friction coefficient on the initial stability of the acetabular cup. In addition, we planed to quantify the effects of eccentric screwing on the cup stability. Finally, we tried to develop a single-image-based navigation system for the acetabular cup.

This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone stiffness, and friction coefficient on the initial stability during the performance of six activities of daily living. A commercially available hemispherical acetabular cup with five screw holes was used as the target model. The elastic modulus of the pelvis and the friction coefficient between cup and pelvic bone were systematically varied within a realistic range to assess the initial stability of the acetabular cup. The simulations showed that peak micromotion occurred at the cup rim and each inserted screw provides only a localized reduction in the relative micromotion between the cup and pelvis. The placement of multiple screws therefore suggested to put near the cup perimeter to effective reduce the peak micromotion, and with adequate spacing between them to cover various loading modes. The initial stability of the acetabular cup decreased nonlinearly with the decrease in the pelvic elastic modulus, and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient plays a less important role than the bone stiffness in resisting relative micromotion between the cup–pelvis interface.

To investigate the effects of screw eccentricity, hemispherical cups were fixed into the blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity: a 1-mm offset, and angular eccentricities of 15o and 25o were evaluated to identify the influence in initial stability. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing, i.e. without eccentricity. An angular eccentricity of 15o did not affect the cup stability when fixation with one or two screws. However, the presence of 25o of angular eccentricity significantly reduced the cup stability, while 1 mm of offset eccentricity had an even greater impact. These results should provide some guideline for surgeons when performing screw insertions in THR.

Besides cup loosening, incorrect angular placement of the acetabular cup in THR induces femoral head dislocation. Computer-assisted navigation systems to aid acetabular cup placement have been developed in the past decade, but their cost has prevented the adoption in clinical practice. In this study, a novel algorithm for determining the data points position in three-dimension from a single planar image was developed. This algorithm was employed in the development of a low-cost intrasurgical cup navigation system. This system consists of four main components: one digital camera, one laptop, one movable trolley cart, and two assisting guide frames. In vitro laboratory validation tests indicated that the possible orientation errors induced by the prototype system were less than 1.9o in abduction and 1.4o in anteversion. Although this system for acetabular cup placement is in the early phase of development, it is clear that the minimal hardware requirement (and hence low cost) of this navigation system makes it suitable for the training and evaluation of inexperienced doctors.

ABSTRACT……………………………………………………I
中文摘要…………………………………………………III
誌謝…………………………………………………………V
CONTENTS…………………………………………………VII
LIST OF FIGURES…………………………………………IX
LIST OF TABLES…………………………………………XII

PREFACE………………………………………………………1
CHAPTER 1. GENERAL INTRODUCTION…………2
1.1 OVERVIEWS OF TOTAL HIP REPLACEMENT……………2
1.2 LITERATURE REVIEWS……………………………………………………9
1.2.1 Relationship between the Initial Stability and Bone Ingrowth ………………9
1.2.2 Biomechanical Analysis of Screw Fixations10
1.2.3 Mechanical Properties of Bone………………15
1.2.4 Friction Coefficient of the Acetabular Cup17
1.2.5 Effect of Screw Eccentricity on Stability ……………………………………………… 19
1.2.6 Orientation of the Inserted Acetabular Cup…………………………………………20
1.2.7 Computer-Assisted Navigation System for the Acetabular Cup……………………20
1.3 MOTIVATION AND OBJECTIVES………………………23

CHAPTER 2. THE EFFECT OF MECHANICAL FACTORS ON THE INITIAL STABILITY OF ACETABULAR CUP………………………………………………………25
2.1 INTRODUCTION………………………………………………25
2.2 MATERIALS AND METHODS……………………………27
2.2.1 Modeling of the Pelvis and Acetabular Components……………27
2.2.2 Loading Conditions and Boundary Conditions……………………………31
2.2.3 Numbers of Screws………………………………33
2.2.4 Bone Stiffness……………………………………33
2.2.5 Friction Coefficient……………………………34
2.2.6 Evaluation Indexes………………………………34
2.3 RESULTS………………………………………………36
2.4 DISCUSSION……………………………………………44
2.5 SUMMARY………………………………………………51

CHAPTER 3. EFFECTS OF SCREW ECCENTRICITY ON THE INITIAL STABILITY OF THE ACETABULAR CUP………………………………………………52
3.1 INTRODUCTION………………………………………………52
3.2 MATERIALS AND METHODS……………………………53
3.2.1 Types of Screw Eccentricity ………………53
3.2.2 Experimental Setups……………………………56
3.3 RESULTS………………………………………………60
3.4 DISCUSSION………………………………………62
3.5 SUMMARY………………………………………………65

CHAPTER 4. COMPUTER-ASSISTED NAVIGATION FOR ACETABULAR CUP PLACEMENT………………………………………………66
4.1 INTRODUCTION…………………………………………66
4.2 SINGLE-IMAGE-BASED ALGORITHM………………………………………………68
4.3 DEVELOPMENT AND VALIDATION OF THE CUP NAVIGATION SYSTEM…72
4.3.1 Hardware and Software…………………………72
4.3.2 Surgical Procedure………………………………76
4.3.3 System Validation………………………………78
4.4 SUMMARY………………………………………………81

CHAPTER 5. CONCLUSIONS AND FUTURE WORK…………………………………82
5.1 ONCLUSIONS……………………………………………82
5.2 FUTURE WORK…………………………………………84

REFERENCES…………………………………………………85
BRIEF PERSONAL INTRODUCTION…………………………95
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