科技與醫療的進步使得全世界老年人口急遽上升，伴隨而來的骨質疏鬆症已成為全世界第二大的流行疾病。IOF於2000年統計指出全球有900萬人因骨質疏鬆而骨折，髖關節骨折占了160萬；預計2050年因骨質疏鬆而產生髖關節骨折的人數將高達626萬人次。中華民國健保局1996~2000年統計資料顯示：台灣人民髖部骨折的發生率高於亞洲其他國家。DHS為臨床上常用來固定近端股骨骨折的內固定器，然而因骨質疏鬆產生的近端股骨骨折型態常為不穩定骨折，破碎的小轉子受到體重負載及肌肉牽引易脫離復位後位置，使負載全經由DHS傳遞因而容易造成cut-out現象發生且延遲骨釘的植入位置會影響力量的傳遞型態及骨釘能否鎖固於股骨頭，目前臨床上DHS的植入導引器械須經由反覆的X光輔助定位，才可將延遲骨釘植入指定位置，使臨床人員與病患暴露在過量的放射線環境。因此本研究針對骨質疏鬆及不穩定的近端股骨骨折設計新型DHS及輔助DHS植入的導引器械，並探討新型DHS模組植入骨鬆且不穩定骨折時，股骨頭內之相關力學分析。特定目標為：(1)設計新型DHS模組及其輔助植入的導引器械；(2)探討不同角度的DHS與TAD植入位置對股骨頭的應力分佈及位移情形；(3)使用wires輔助新型DHS固定骨鬆且不穩定之近端股骨骨折的生物力學分析。

新型DHS必須搭配wires使用來固定破碎的小轉子，且為使wires不易滑脫於光滑的骨板，因此在骨板上方設計可讓wires附著的溝槽，利用CAD來實現新型DHS的初始設計及模型的建立，並使用有限元素法依據ASTM F384及F382 設置其邊界條件，進而評估新型DHS的結構強度。股骨模型是由CT影像重建軟體所建構而成，將股骨與新型DHS模型一同匯入有限元素分析軟體內，分別給予材料性質及邊界條件來模擬新型DHS植入骨鬆且不穩定的近端股骨的生物力學特性，探討不同DHS角度、TAD植入位置及加入wires固定破碎小轉子後，股骨頭內部應力分布及骨折處位移情形。為使延遲骨釘精準且快速植入股骨頭內指定位置進而研發新型導引器械，其有兩項創新之功能性設計分別為導引鋼條及可選擇式k-pin穿越孔，利用CAD來實現模型的初始設計，而後使用RP快速成型製作導引器械的雛型。

本研究ASTM F384有角度內固定器模擬結果顯示：應力最大值發生於DHS的側板與套筒連接處，這是由於結構不連續所造成而新型DHS骨板設計的溝槽並不會影響結構強度。ASTM F382骨板四點彎距模擬結果顯示：最大應力值發生於骨板的最外圍，此為曲率最大位置。新型DHS的生物力學模擬結果顯示：植入角度較大的DHS，股骨頭內部會承受較大的應力；延遲骨釘植入TAD值較大的位置，股骨頭內部最大應力值及整體股骨位移量均呈現較大的趨勢，尤其以植入位置偏前及偏後的組別最為明顯；使用wires固定破碎的小轉子後，使得不穩定的股骨骨折型態趨近於穩定股骨骨折的型態，因此可提高骨折處的穩定度而降低骨股頭內部的最大應力值及斷裂的股骨頭位移量。

未來研究方向建議：(1) 製作新型導引器械的不鏽鋼雛型，申請IRB臨床人體試驗確認新型導引器械的功能性，(2) 製作新型DHS的不鏽鋼雛型，參照ASTM機械性質測試規範檢測其機械性質，並購買sawbone進行生物力學實驗，探討新型DHS的生物力學特性。

Technology and medical advances make the elderly population in the world increase rapidly, accompanied by osteoporosis has become the second largest epidemics in the world. According to the data from the international osteoporosis foundation (IOF) in 2000, there were 9 million people in the world suffered from osteoporosis-related fractures, and 1.6 million of them were hip fractures. Moreover, the people with osteoporosis-related hip fractures will come to 6.26 million in 2050. The data from Taiwan Health Insurance Department during 1996~2000 revealed that the people in Taiwan had higher incidence of hip fractures than the people in other Asian countries. Dynamic Hip Screw (DHS) is a common device of internal fixation for proximal femoral fractures. Proximal femoral fractures resulting from osteoporosis are often unstable. Broken pieces of the lesser trochanter usually dislocate from original locations as a result of the load of body weight and muscle traction. Therefore, the DHS bears the entire load resulting in cut-out phenomenon. The implanted position of lag screws will affect the transfer patterns of the load as well as the stability of screws in the femoral head. Orientation assisted with repeated X-ray is necessary for current guidance devices of DHS implantation to implant lag screws into specific location of the femoral head. That will increase the risk of radial exposure. The purpose of this investigation is to design a new DHS and develop a guidance device of DHS implantation for patients with unstable proximal femoral fractures and osteoporosis. The specific aims include (1) modeling design of the new DHS and the guidance device, (2) investigation of stress distribution and displacement of fractures in the femoral head with variant angle of the DHS and tip apex distance (TAD) value, (3) and biomechanical analysis of unstable proximal femoral fractures with osteoporosis under the fixation of the new DHS with wires.

The new DHS was designed to use wires to fix the broken pieces of the lesser trochanter. Therefore, a groove was created on the bone plate to allow the attachment of wires. Computer-aided design (CAD) was used for modeling and initial design. The boundary conditions of finite element analysis were set following the specification of American Society for Testing Material (ASTM) F384 and F382 to assess the mechanical properties of the DHS. Implantation of the new DHS in unstable proximal femoral fractures with osteoporosis was simulated to explore the stress distribution within the femoral head as well as the displacement of the fractures under the conditions with variant angles and locations of TAD implantation. The effect of wires on fixing lesser trochanter was also simulated. For the purpose of lag screws could be accurately and quickly implanted into specific locations, a new guidance device was developed. The guidance device included two innovative designs: a guidance steel bar and selectable holes for k-pin. The initial model was constructed by CAD, and the prototype was created with rapid prototyping.

The mechanical properties of the DHS simulation with the specification of ASTM revealed that the maximal stress occurred in the junction of DHS slide plate and barrel as a result of the discontinued structures. The groove created on the bone plate of the new DHS didn’t diminish structural strength of the plate. Bending test of the ASTM F382 showed the maximal stress appeared in the margin of bone plate, which was the location with the maximal curvature. Biomechanics simulation showed that when the angle of DHS implantation expanded, the stress within the femoral head would simultaneously increase. Furthermore, the stress distribution within the femoral head and the displacement of fractures would increase when lag screws were implanted into locations with high TAD value. This phenomenon was especially obvious in the groups with extremely anterior or posterior implantation. Fixation of the broken pieces of the lesser trochanter with wires could improve the stability of the fractures.
Here are some recommendations for further investigations. First, manufactory of prototype of the new guidance device with stainless steel as well as it’s application in clinical trials should be progressed to verify the functionality of the new device. Second, prototype of the new DHS with stainless steel would be manufactured. The mechanical properties of the new DHS would be test according to the ASTM standard specifications and test methods. Meanwhile, biomechanical studies with sawbone may be necessary to explore the biomechanical properties of the new DHS.

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