迦瑪骨釘(Gamma nail)和滑動式螺絲骨板(sliding screw plate)已廣泛的應用於治療股骨近心端骨折，從臨床觀察中發現，在骨折治療過程中植入物會發生的失效模式有破壞和鬆脫等情形，且近端股骨可能會因植入物的影響而發生骨切效應風險(Cut-out)。本文主要是利用有限元素模擬分析軟體來評估市售二種骨科植入物(Gamma nail與滑動式螺絲骨板)與自行研發設計之雙螺絲骨釘在臨床上的使用性能及討論其設計之優劣。
在有限元素分析中，股骨模型經由電腦斷層掃描(CT scan)取得骨結構幾何斷面，並經由影像之處理後轉檔輸入至有限元素分析套裝軟體ANSYS中，且以ANSYS建立的三維有限元素分析模型有股骨和植入物。植入物的楊氏係數為230GPa，浦松比為0.3 ; 骨骼之楊氏係數為硬質骨17GPa、鬆質骨0.36GPa，浦松比均為0.3，分析模型之受力與邊界條件為在股骨頭上施加髖關節反力與大轉子上施加肌肉力，以及將股骨遠端表面完全拘束住，植入物與骨骼之界面以接觸元素作模擬，分別考慮二種骨折條件包括:股骨頸骨折與股骨轉子下骨折。於後處理分析上擷取的結果有von Mises應力、股骨位移量和股骨近端骨骼總應變能量(total strain energy)。
從有限元素分析結果中得知骨釘和骨板的von Mises應力都比遲滯螺絲和鎖定螺絲高，且雙螺絲骨釘因為有較小的von Mise應力，所以雙螺絲骨釘有較低的損壞率。而滑動式螺絲骨板因為有較高的股骨近端骨骼總應變能量，所以滑動式螺絲骨板有較高的骨切效應風險。雙螺絲骨釘可以避免迦瑪骨釘在股骨幹產生的應力集中，又能減少滑動式螺絲骨板所產生的高骨切效應風險。本研究所建立之有限元素分析模型可反應出臨床上的觀察結果，且希望本研究可以幫助工程師在股骨內固定器設計上及骨科醫師在臨床使用上之參考依據。

The gamma nail and sliding screw plate have been applied for the treatment of proximal femoral fracture. In the clinical point of view, the implants may fail and cause loss of fracture fixation and impairment of fracture healing. In addition, the proximal femur may be cut out by those implants. In this study, two types of commercial available implants (gamma nail and sliding screw plate) and a newly designed implant (double screw nail) were assessed by finite element analysis. The purposes of this study were to evaluate the performance of these fracture fixators and to discuss the effects of the implants’ geometry and dimension.
In finite element analysis, in accordance with the bone structures and geometry gained from a computed tomography (CT) scan, the anatomical shape for femur was created. Then the CT scan models were transformed into three-dimensional solid models by image processing and Boolean operation. The finite element models which consisted of the femur and implant were established by commercial software ANSYS. The young’s modulus and Poisson’s ratio for the implants were 230 GPa and 0.3 respectively. The young’s modulus for cortical bone was 17 GPa and for cancellous bone was 0.36 GPa. The Poisson’s ratio was 0.3 for both cortical bone and cancellous bone. A joint reaction force which was applied at the center of femoral head and an abductor muscle force which was applied at the greater trochanter were used and the end of distal femur was fully constrained. Contact elements were used for the interfaces between the implant and femur. Two kinds of fracture were discussed including femoral neck fracture and subtrochanter fracture. In postprocessing, the von Mises stress, deflection, total strain energy were derived.
From the results of finite element analysis, the von Mises stress of the nails and plate were greater than that of lag screws and locking screws. The double screw nail had smallest von Mises stress. It meant that the double screw nail had lowest risk of implant failure. The sliding screw plate had largest total strain energy of proximal femur. It implied that the sliding screw plate had highest risk of bone cut-out. The double screw nail could eliminate the stress concentration at the femoral shaft as compared with the gamma nail and decrease the risk of bone cut out as compared with sliding screw plate. Developing the finite element models in this study could reflect the clinical observation. This study could assist the engineers to design new orthopedics implants and help the surgeons select suitable orthopedics implants for their patients.

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