臺灣博碩士論文加值系統

單髁人工膝關節發展至今已相當成熟，讓僅有單側關節發生嚴重損壞之病患，除了高位脛骨截骨術和全人工膝關節置換術外，又多了一項手術治療的選擇。但是從最近有關單髁人工膝關節置換手術的臨床追蹤報告顯示，因聚乙烯脛骨元件磨損而引發骨溶解及無菌性鬆脫併發症之問題卻始終存在，因此如何減低，甚至避免聚乙烯脛骨元件損壞的問題，值得進一步深入探討。然而，造成聚乙烯脛骨元件磨損之原因中，絕大部分是源自於過高的應力，而應力過高之主要原因，則應與元件間之對位、植入物設計、聚乙烯厚度及接觸負載有關。有鑑於此，本研究擬藉由有限元素分析之技術，來探討單髁人工膝關節在各種植入狀態條件時對聚乙烯脛骨元件所造成之影響，進而以提供未來臨床醫師手術之參考。
因此，為研究探討聚乙烯脛骨元件之磨耗行為，本研究將採用不同設計之單髁人工膝關節在屈膝 0°的步態行為下，施以 1435 N之淨負荷在內髁關節面上，以進行各項影響因子分析，其中包括有膝內翻傾斜分析、脛骨後傾分析、脛骨內/外翻傾斜分析、聚乙烯厚度及膝關節接觸力改變分析。最後從分析結果得知，在膝內翻校正方面，聚乙烯脛骨元件在接觸後所產生之應力值，皆會隨著膝內翻傾斜角度的增加而增加，接觸中心且有稍微向外偏移之現象，但並不會因後傾角度改變而有重大改變，除此之外，在傾斜15°時有最大應力值產生，而且在所有的對位角度上所產生之應力值，也均會超過超高分子量聚乙烯材料所能承受之降伏強度值，值得一提的，任何傾斜角之最大應力值並非發生在關節之接觸表面，而是發生在接觸表面下方約 2 mm 處，由這結果得知，聚乙烯的初始破壞機轉是發生在元件內部，且是由內而逐漸向接觸表面產生層裂破壞。
關於脛骨不當骨切而造成脛骨內/外翻傾斜方面，從分析結果得知，相較於對稱式單髁人工膝關節，解剖式在脛骨內翻傾斜上較能容許手術時所產生之對位誤差，但在脛骨外翻傾斜方面則仍需避免超過10°以上之誤差；另一方面，若內/外翻傾斜在約5°以內時，使用對稱式單髁人工膝關節時，也可以與解剖式者達到一樣之效果。
另外，在增加聚乙烯厚度以改善應力破壞方面，從模擬分析結果得知，若增加聚乙烯厚度，聚乙烯應力值雖可略為下降，但由本研究之分析發現，該應力減少量並不顯著。再者，由膝關節接觸負載變化與材質降伏強度比較方面，從分析結果得知，單髁聚乙烯元件之承載條件應以不超過 800 N為宜，否則不管採用之聚乙烯元件形式為何，其使用壽命堪慮。為了進一步確認本結論，研究中也已體外實驗加以驗證，實驗結果也顯示，前述之最大承載條件 800 N是一值得信賴的限制條件。簡言之，體位約超過 56 kg 者，由本研究之結果顯示，並不適用於單髁人工膝關節置換手術。根據本項研究結果，本研究也提出一簡易篩選公式，供醫師選用較適宜之聚乙烯元件。
從本研究結果得知，單髁人工膝關節在膝關節過度的活動行為、體位過重、膝內翻校正不足及脛骨不當骨切時，確實對聚乙烯脛骨元件之磨耗，有相當大之影響，其中以前二者影響最巨，但關於聚乙烯厚度及後傾角度改變方面則影響不大。因此，經由上述多種影響因子之交叉分析結果得知，醫生未來在UKA如要有出色的長遠結果及降低二次置換手術之發生率，除在元件間的對位和手術精確性有所改善外，病患的體重及日常活動行為更需加以審慎評估，因此，就現階段而言，本研究則不建議將UKA作為體重較重、年紀較輕及活動力較高之膝關節炎患者當作主要的手術治療選項。

Unicompartmental knee arthroplasty (UKA) gradually becomes a promising alternative treatment to high tibial osteotomy in patients with unicondylar involvement, in addition to the total knee arthroplasty. In lots of previous series, osteolysis and aseptic loosening were continued to plague surgeons. Insert wearing is considered one of the major causes. The purpose of this study intends to clarify the main relations of the insert wearing to factors like implant designs, alignment of components, and contact forces. In the present study, the finite element analysis (FEA) was used to study the stress distributions of polyethylene (PE) component and to explore the possible wear mechanism.
In order to evaluate the wear behavior of a tibial insert, three-dimensional FE models of different designs of unicompartmental knee prostheses (UKP) are constructed to investigate the effects of mal-resection including varus/valgus tilts, and posterior slopes, PE properties as well as contact forces applying on it. Through the study, all material properties of the components are set as close those currently used as possible. And, a 1435 N compression load is applied from the top of medial unicondyle knee at zero degree of flexion.
In the correction of varus deformity, the tibial insert has the highest stress at the 15∘varus tilt. In addition, the stress demonstrates no significant difference in response to changes of posterior slopes. Or, the maximal stresses occur at the center of the contacts and are located ca. 2 mm beneath the articulating surface. This result implies that the failure mechanism of the tibial insert initially takes place inside the PE, and then gradually propagates into cracks or flakes from the inside to the contact surface. Furthermore, the maximal stress of the tibial insert shifts laterally with the increasing varus angles. Regardless of varus tilts, the stresses always exceed the yield strength of PE under the gait loading condition.
In cases of mal-resection on the tibial plateau in the coronal plane, it was found that anatomically designed unicompartmental knee prosthesis (UKP) can allow more positional errors in varus tilts than that of a symmetrically designed one. However, both should avoid any positional error greater than 5° varus/valgus tilts. Otherwise, it may result in severe wear on its PE component.
Since there exist several choices of the PE thickness, the present study also investigates the possibility of increasing thickness to reduce the maximal stress. However, the results of in vivo FE simulations have revealed that a thicker PE insert may not be a good alternative in the sense of reducing PE wear. In fact, a thicker PE component makes almost no significant reduction to the stress of all insert samples. The PE stress increasing strongly depends on the load that applying onto it, instead of its thickness. As a conclusion, the present study would suggest that loading on the medial unicondyle should avoid greater than ca. 800 N. Or, the life of the PE insert may be jeopardized. This threshold value of 800 N has been further verified by the in vitro experiment. In other words, the study suggests that the UKA is more adequate for those of body weights less than ca. 56 kg. In order to give this conclusion more solid, the present report also provide a simply mathematical model for surgeons to select appropriate patients so that a better UKA outcome can be achieved.
Overall, the results of present study have shown that the wear of PE tibial components have considerable impacts to UKP, such as joint overuse, overweight, under-/over- corrections of varus deformity and tibial mal-resection. However, the influences of PE thickness and the posterior slopes are minor and can be ignored. For UKA to have excellent long-term results, the body weight, the alignment of components, and accurate technique of surgery will all be required. Nevertheless, under the current circumstances, UKA is not recommended for the over-weighted, young patients or those with excessive activities. Meanwhile, the constraint given from the present study can be a good guild line for the selection of patients.

中文摘要 i
英文摘要 iii
誌謝 v
目錄 vi
表目錄 viii
圖目錄 ix
第一章 前言 1
1.1 導論 1
1.2 微創手術 3
1.2.1 微創手術方法 4
1.3 研究背景及文獻探討 7
1.4 研究目的 11
第二章 研究方法及步驟 12
2.1單髁人工膝關節體外測試 12
2.1.1 測試材料 14
2.1.2 治具之設計與製作 17
2.1.3 單髁人工膝關節測試 19
2.2單髁人工膝關節三維實體模型之建立 22
2.2.1 物件量測 22
2.2.2 量測資料定位與合併 24
2.2.3 物件曲面及實體建構 24
2.3 有限元素分析 33
2.3.1 有限元素模型之建立 33
2.3.2 體外測試模擬分析 38
2.3.3 股骨內翻及脛骨後傾對位分析 38
2.3.4 脛骨平台不當骨切分析 40
2.3.5 脛骨元件厚度影響分析 41
2.3.6 不同膝關節負載條件之應力分析 43
第三章 研究結果 44
3.1體外測試及有限元素接觸模擬結果比較 44
3.2股骨內翻及脛骨後傾對位時之應力分析結果 49
3.2.1 股骨元件內翻及脛骨後傾時之蒙麥斯應力 49
3.2.2 股骨元件內翻及脛骨後傾時之接觸應力 57
3.3脛骨平台不當骨切時之應力分析結果 60
3.3.1 脛骨內/外翻傾斜時之蒙麥斯應力 60
3.3.2 脛骨內/外翻傾斜時之接觸應力 63
3.4脛骨元件厚度改變之應力分析結果 65
3.5不同膝關節負載條件之應力分析結果 68
第四章 討論 71
4.1股骨內翻及脛骨後傾對位時之應力影響 71
4.2脛骨平台不當骨切時之應力影響 74
4.3脛骨元件厚度改變之應力影響 77
4.4不同膝關節負載條件之應力比較 79
第五章 結論 82
參考文獻 84

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