椎弓根骨螺絲在現今的醫療中已經廣泛的使用於治療脊椎的退化性疾病以及脊椎椎骨的骨折，然而椎弓根骨螺絲植入脊椎後容易因為脊椎反覆的運動與彎曲造成椎弓根骨螺絲的破斷，為了避免椎弓根骨螺絲植入脊椎後發生破斷的情況，研究椎弓根骨螺絲的彎曲強度是至關重要的。過去針對椎弓根骨螺絲彎曲強度的研究其骨螺絲大部分是以傳統的切削加工製成的，本研究的椎弓根骨螺絲則是以積層製造的方式製成的。積層製造近年來廣泛的應用在生醫材料以及其他各個領域。積層製造相較於傳統加工具有成型快速、減少材料浪費，以及可以製作幾何形狀複雜的製品等等優勢，以積層製造製作骨科植入物可針對病人的骨骼型態製作出客製化的植入物。本研究的積層製造椎弓根骨螺絲若具有好的彎曲強度將提供骨科醫師與脊椎疾病患者一項嶄新的選擇。本研究使用有限元素分析以及生物力學機械測試進行積層製造椎弓根骨螺絲彎曲強度的研究，針對椎弓根骨螺絲螺紋幾何參數的不同進行彎曲強度的探討。
本研究有限元素分析的部分首先針對椎弓根骨螺絲螺紋不同近端根部弧角半徑與遠端根部弧角半徑的大小進行彎曲強度的探討，再來則是針對椎弓根骨螺絲螺紋不同內徑大小與螺紋不同錐度起始位置進行彎曲強度的探討。有限元素分析的結果發現具有越大的根部弧角半徑、越大的螺紋內徑，以及螺紋具有錐度的部分越多，椎弓根骨螺絲的彎曲強度越大。
本研究接著進行積層製造椎弓根骨螺絲彎曲強度的生物力學測試，針對椎弓根骨螺絲螺紋不同內徑大小與螺紋不同錐度起始位置進行降伏強度以及疲勞強度的測試與分析。降伏測試與疲勞測試的結果與有限元素分析的結果呈現相同的趨勢，即越大的骨螺絲螺紋內徑，以及骨螺絲螺紋具有錐度的部分越多，降伏強度與疲勞強度皆越大。然而與過去以切削加工製作的椎弓根骨螺絲之彎曲強度測試結果進行比較，本研究以積層製造製作的椎弓根骨螺絲其疲勞強度明顯低於切削加工製作的椎弓根骨螺絲，故針對積層製造椎弓根骨螺絲進行熱處理，並再次進行疲勞強度的測試，探討熱處理是否對骨螺絲的疲勞壽命有幫助。結果發現熱處理後相較於熱處理前增加了約69%的疲勞壽命，但是仍無法達到與切削加工的骨螺絲一樣的疲勞壽命，因此積層製造椎弓根骨螺絲仍具有較大的破斷風險，其臨床適用性仍不如切削加工的椎弓根骨螺絲。

Pedicle screws are currently widely used in medical treatment for spinal degenerative diseases and vertebrae fractures. However, implanted pedicle screws can easily rupture due to repeated movement and bending of the spine. The bending strength of a pedicle screw is therefore crucial and should be studied to avoid rupture of the pedicle screw after implantation into the spine. Most pedicle screws in relevant studies focusing on the bending strength have been made through conventional machining, but the pedicle screw used in this study was made using additive manufacturing. Additive manufacturing has been widely applied in biomedical materials and other fields in recent years. Compared with conventional machining, additive manufacturing has advantages including rapid molding, reduced material waste, and the ability to produce products with complex geometric shapes. The orthopedic implants made through additive manufacturing can produce customized implants according to each patient’s bone status. The additive manufactured pedicle screw proposed in this study, which has excellent bending strength, may provide a new option for orthopedic physicians and patients with spinal diseases. In this study, a finite element analysis and biomechanical testing were used to study the bending strength of the additive manufactured pedicle screw. The bending strength of the pedicle screw with respect to the geometric parameters of the screw thread was also investigated.
In the finite element analysis, the bending strength of the pedicle screw with varying proximal and distal root radiuses was first investigated. Subsequently, the bending strength of the pedicle screw with varying thread inner diameters and taper start positions was also discussed. The results revealed that the bending strength of the pedicle screw was greater when the root radius and thread inner diameter were larger and had more tapers.
In addition, this study performed a biomechanical test of the bending strength of the pedicle screw. Tests and analyses of the yield strength and fatigue strength of the pedicle screw with varying inner diameters and taper start positions were performed. The results of the yield and fatigue tests revealed a similar trend to the results of the finite element analysis, namely that a large inner diameter of the pedicle screw and number of tapers on the pedicle screw thread correspond to a high yield strength and fatigue strength. However, results indicated that compared with the bending strength of a pedicle screw made through conventional machining, the proposed pedicle screw made through additive manufacturing exhibited a lower fatigue strength. Therefore, heat treatment was performed on the additive manufactured pedicle screw before the fatigue strength was tested again to investigate whether heat treatment was helpful for improving the fatigue life of the pedicle screw. The result revealed that the fatigue life of the screw was increased by approximately 69% after the heat treatment, but the fatigue life was still shorter than that of the conventional machined pedicle screw. Accordingly, the additive manufactured pedicle screw possessed a relatively high risk of rupture. Therefore, its clinical applicability is not as satisfactory as that of the pedicle screw made through conventional machining.

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