目前市面上鎖定式骨髓內釘已被廣泛的利用在治療下肢長骨骨折，因其擁有將骨折處附近的軟組織傷害減到最低，並且穩定骨折處的優點。在臨床的應用上，鎖定螺絲最常發生的破壞模式為破斷與鬆脫，而骨髓內釘最常發生破壞的地方位於內釘上的螺絲孔，造成了骨折固定的失效、延遲癒合或不癒合。根據目前的研究，在市面上的植入物，包括鎖定螺絲與鎖定內釘，由於幾何設計變異性較大且材質不同，故無法公平地去比較。因此，本研究自行設計與製作螺絲與內釘，藉此評估植入物的幾何設計參數與材料對機械性能的影響。
在本研究中，股骨鎖定螺絲以生物力學分析，包括生物力學測試與有限元素分析，來評估十六種螺絲設計。藉由降伏測試與疲勞測試來評估彎曲強度，並利用三維有限元素分析來模擬生物力學測試的結果。而在鎖定內釘的生物力學分析中，設計十二種內釘模型，利用三維有限元素分析來模擬彎曲強度。
由股骨螺絲之生物力學分析結果中得知，當股骨螺絲的內徑越大、根部導圓角半徑越大，則有較高的降伏負載及疲勞強度。若股骨螺絲為鈦合金，則疲勞壽命會明顯提升。而生物力學實驗與有限元素模擬有不錯的相關係數，故可利用有限元素分析來準確預估生物力學測試結果。而鎖定內釘在外徑較大以及內釘上的螺絲孔徑較小時，有較低的最大張應力。
本論文中，股骨螺絲與鎖定內釘的幾何參數與研究成果，可提供往後工程界或醫學界研發人員，創新與設計新型植入物的重要參考與依據。

An interlocking nail, which has advantages of minimal soft tissue injury and stable fracture fixation, has been widely used to treat femoral shaft fracture. In clinical application, screw breakage and screw loosening are two main failure modes and nail hole is the weakest portion of an interlocking nail. These breakdowns may cause loss of fracture fixation, delayed union, and non-union. According to the previous researches, the commercial available implants including locking screws and interlocking nails were used in their study, but those implants with the different dimensions and materials could not be fairly compared. Therefore, in this study, the screws and nails are specially designed and manufactured. The effects of design geometry and materials on the mechanical performance of the locking screws and nails are investigated.
In biomechanical analyses of femoral locking screws, sixteen types of locking screws were designed and manufactured. The bending strength was assessed by yielding tests and fatigue tests. Three-dimensional finite element models were established to simulate the results of biomechanical tests. In biomechanical analyses of interlocking nails, twelve types of interlocking nails were designed. Three-dimensional finite element models were created to evaluate their bending strength.
From the results of femoral locking screws, the screws with larger inner diameter and root radius have higher yielding load and fatigue life. Titanium femoral locking screw could significantly increase its fatigue strength. The analytical results of femoral locking screw models were closely related to those of biomechanical tests with high correlation coefficient. From the results of interlocking nails, the nails with larger outer diameter and smaller nail hole have lower maximal tensile stress.
The results of this study could help surgeons in selecting suitable devices for their patients and assist design engineers in developing new orthopaedic implants.

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