鎖定式骨髓內釘已經被廣泛利用於治療股骨近端骨折，但仍然有遲滯螺絲斷裂與鬆脫的失效模式。因此，必須進行花費額外金錢與時間且造成病人二次傷害的二次手術。本研究的目的在於改良雙螺絲骨釘遲滯螺絲的設計，使其可以同時具有彎曲強度與拉出強度。
本研究首先利用田口L25直交表定義遲滯螺絲設計區間，並使用有限元素分析求解彎曲模型與拉出模型。接著透過類神經網路建立預測彎曲目標與拉出目標的數學模型供給遺傳演算法尋求遲滯螺絲最佳化設計，並以生物力學測試驗證。
本研究中所得的最佳化遲滯螺絲設計因子為圓錐起始位置0 mm、內徑3.3 mm、近端根部半徑0.22 mm、螺紋節距3.3 mm、近端半角5°與螺紋厚度0.2 mm。有限元素分析彎曲模型最大張應力結果由高至低為市售遲滯螺絲、L23遲滯螺絲、L16遲滯螺絲、最佳化遲滯螺絲與L5遲滯螺絲（455.36-1312.10 MPa）；拉出模型總反作用力結果由高至低為最佳化遲滯螺絲、市售遲滯螺絲、L16遲滯螺絲、L23遲滯螺絲與L5遲滯螺絲（23.61-38.14 N）。生物力學測試部份，彎曲測試降伏負載結果由高至低為L5遲滯螺絲、最佳化遲滯螺絲、L16遲滯螺絲、L23遲滯螺絲與市售遲滯螺絲（454.08-605.01 N）；疲勞測試疲勞壽命結果由高至低為最佳化遲滯螺絲、L5遲滯螺絲L16遲滯螺絲、L23遲滯螺絲與市售遲滯螺絲（80339-1000000 cycles）；拉出測試在0.32與0.16 g/cm3人造假骨密度中拉出強度結果由高至低為最佳化遲滯螺絲、市售遲滯螺絲、L16遲滯螺絲、L23遲滯螺絲與L5遲滯螺絲（964.31-1635.36 N）以及L16遲滯螺絲、最佳化遲滯螺絲、市售遲滯螺絲、L23遲滯螺絲與L5遲滯螺絲（299.09-661.12 N）。彎曲測試降伏負載與彎曲模型總應變能結果相關係數為-1.00，疲勞測試疲勞壽命對數值與彎曲模型最大張應力結果相關係數為-0.91，拉出測試拉出強度與拉出模型總反作用力結果相關係數在0.32與0.16 g/cm3人造假骨密度中分別為0.99與0.93。
本研究中，對於彎曲強度具有影響力的設計因子為圓錐起始位置和內徑，而對於拉出強度具有影響力的設計因子為內徑、近端根部半徑和螺紋節距。由類神經網路以及遺傳演算法可知，最佳化遲滯螺絲能夠同時保有95％的彎曲強度與拉出強度。

Interlocking intramedullary nail had been widely used in proximal femoral fractures, but it still threatened by lag screw failures, including breakage and loosening. It is necessary to perform the second surgery when implant failure occurred. The second surgery costs additional time and money, and it also causes the additional injury to the patients. The purpose of this study is to improve the lag screw design, and to find an optimal design which can maintain bending and pullout strength simultaneously.
This study used Taguchi L25 orthogonal array to define the design space of lag screws, and used finite element analysis (FEA) to solve the bending and pullout models. The results of FEA were used to construct artificial neural network (ANN). We chose the best ANN model to perform multi-objective genetic algorithms (GA), and determined the optimal design of lag screw. Finally, we chose five different lag screw designs (L5 screw, L16 screw, L23 screw, commercial screw, and optimal screw) to perform biomechanical tests, and prove the optimal design which can maintain bending and pullout strength simultaneously.
In this study, we defined the optimal design from GA results, the six factors were initial position of conical angle 29 mm, inner diameter 3.3 mm, proximal root radius 0.22 mm, pitch 3.3 mm, proximal half angle 5°, thread width 0.2 mm. From the FEA results, the maximum tensile stress of bending models descended as commercial screw, L23 screw, L16 screw, optimal screw, and L5 screw (455.36-1312.10 MPa); and total reaction force of pullout models descended as optimal screw, commercial screw, L16 screw, L23 screw, and L5 screw (23.61-38.14 N). Further, from biomechanical tests, the yielding load descended as L5 screw, optimal screw, L16 screw, L23 screw, and commercial screw (454.08-605.01 N); the fatigue life descended as optimal screw, L5 screw, L16 screw, L23 screw, and commercial screw (80339-1000000 cycles); the pullout strength descended as optimal screw, commercial screw, L16 screw, L23 screw, and L5 screw (964.31-1635.36 N) and L16 screw, optimal screw, commercial screw, L23 screw, and L5 screw (299.09-661.12 N) in 0.32 and 0.16 g/cm3 Sawbone densities. The correlation coefficient between the total strain energy of bending models and the yielding load of bending tests was -1.00; and between the maximum tensile stress of bending models and logarithmic fatigue life of fatigue tests was -0.91; and between the total reaction force of pullout models and pullout strength of pullout tests were 0.99 and 0.93 in 0.32 and 0.16 g/cm3 Sawbone densities .
In this study, the influential factors were initial position of conical angle and inner diameter in bending cases; inner diameter, proximal root radius and pitch in pullout cases. From the results of ANN, GA and biomechanical tests, it showed the optimal lag screw could maintain 95％ of maximal bending and pullout strength simultaneously.

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