鎖定式骨髓內釘系統已成為治療股骨骨幹骨折的標準方法，因為能提供骨折處較佳的穩定度。使用骨髓內釘時，大多會優先採用靜態固定法，然而卻可能因骨折間隙過大，造成骨不癒合。所以考慮動態固定法，以減少骨折間隙幫助骨癒合，但傳統動態固定法因為穩定度不足，可能產生肢骨縮短的情形。因此考慮使用具有長圓孔設計的骨釘，並採取移除一根鎖定螺絲的動態固定法，使其不僅能
有動態固定的優勢還能保有扭轉穩定度。
本研究使用目前廣泛接受的股骨模型及市售的鎖定式骨釘，以有限元素分析
軟體ANSYS評估股骨植入順向性或逆向性骨釘後，不同固定法之生物力學特性，並探討植入物於近端和遠端股骨骨幹骨折時的情形。本研究用來判斷其生物力學性能的準則有兩個，第一個是畸變能準則，主要是觀察植入物產生最大應力值的位置，以了解植入物可能由何處發生損壞；第二個是整體股骨固定穩定度與扭轉穩定度，用來評估幫助骨癒合的重要因素。
分析結果可發現，移除一根鎖定螺絲的固定方式不僅能降低破壞可能性，還能保有穩定度，提高骨癒合率，與臨床上發現採用移除一根鎖定螺絲固定方式的癒合率高於傳統動態固定具有相同趨勢。使用靜態固定法時，比起長圓孔骨釘，傳統骨釘較能降低骨釘損壞可能性且具有較好的穩定度，因此建議採用靜態固定醫治時，使用傳統骨釘較佳。而使用動態固定法時，採用長圓孔骨釘並移除一根鎖定螺絲的固定方式，使骨釘較不易損壞且有較好的扭轉穩定度，因此可證實使用具有長圓孔的骨髓內釘並移除一根鎖定螺絲為最佳的固定方法。
希望藉由本研究所得出的結果，能幫助骨科醫師了解長圓型孔洞設計之骨髓內釘的生物力學特性，並於臨床上選擇固定法時的參考依據。

An interlocking nail system has become a standard treatment for femoral shaft fracture, because of the superiority of better stability over plates. The usual fixation of traditional nail is static fixation for its great stability, however, a traditional nail with static fixation may make femoral fracture nonunion owing to the gaps between fracture fragments. Then, immediate dynamization is regarded as an effective treatment for nonunion. The principle of dynamization with traditional nail is to remove all proximal or distal screws to reduce gaps within fracture fragments and facilitate bone union, but it may decrease rotational stability due to one end fragment without any screw fixation. Thus, consider another effective dynamization with slotted nail, which can just remove one screw and make another screw preserved in the slot hole, not only keeping rotational stability but facilitating bone union. Unfortunately, the biomechanical performance of the interlocking nail systems with the slotted nail has not been investigated mechanically. Therefore, the purpose of this study was to investigate the biomechanical performance of the slotted nail in situation of the static or dynamic fixation techniques using finite element analysis.
The commercial interlocking nails and the standardized femur model were used in this study. The biomechanical characteristics of traditional and slotted nail with static fixation technique and slotted nail with three kinds of dynamic fixation techniques applied to two types of femoral shaft fracture with antegrade and retrograde implanting were compared. To determine the biomechanical characteristics of different fixation techniques, the maximum von Mises stress of the implants；the axial stability and the rotational stability of whole femur were calculated.
The results show that antegrade slotted nail at proximal fracture and retrograde slotted nail at distal fracture with removing one screw get minimum stress of the nail and maximum rotational stability. The dynamization technique with removing one screw gets smaller stress of nail and higher rotational reaction force than removing all screws at one end, that means removing one screw has much higher union rate. The result obtained in this study had the same outcome in clinical findings. The dynamization technique with removing one screw could reduce the stress of the nail and keep the rotational stability. The results of this study could help surgeons to realize the biomechanical characteristics of slotted nail and provide evidence to support the use of fixation techniques.

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