在評估植入物對於人體的運動學及動力學時，常會使用的方法有實際的生物力學實驗或虛擬的有限元素分析，進而得到植入物的效果及影響；在實際實驗中，常會伴隨著浩大的實驗設計與資金，並且資料紀錄與保存較為困難，但對於有限元素分析而言，只需要建構出幾何模型與輸入各項分析參數，就能得出接近於實際測試的結果，除了資料較能數據化之外，還能將所有數據記錄於電腦當中，因此有限元素常被用於醫學領域論文中。
骨融合手術對於脊椎手術固定節與手術鄰近節的效果與影響常被臨床醫生提出討論，而常見的固定器植入方式有傳統軌跡(Traditional Trajectory)與較新型微創手術的皮質骨軌跡(Cortical Bone Trajectory)等兩種，但鮮少有論文直接討論兩者運動學及動力學的差異，大多是比較這兩種手術骨釘的抗拔出應力，或是過分高估手術植入骨釘的直徑或長度，甚至進行有限元素分析的模型太過於簡陋，導致運動學或動力學傳遞上呈現的結果常會有所錯誤或不精準。故本研究使用完整的五節腰椎模型，並且參數化骨釘的直徑、長度及植入軌跡，進行分析比較傳統軌跡與皮質骨軌跡之運動學及動力學的差異與討論。
皮質骨軌跡是目前臨床上最新穎的腰椎微創手術，故許多臨床醫師慢慢以此手術軌跡為主，但其使用的骨釘規格常會受到椎弓根大小的限制，因此在臨床上醫師時常會使用較小的直徑進行手術上的植入，避免打穿椎弓根或是椎體，但在論文參考或本研究分析結果時，常發現此類的骨釘常會因為太細，導致應力過大的情形發生，以至於在實際使用上，骨釘有著可能會斷裂的缺點。因此在本研究中，將會對皮質骨軌跡之骨釘進行改善，設計出一款複合式的骨釘，達到在手術時好植入，且具有不容易斷裂的效果，並透過有限元素分析，與改善前的骨釘進行運動學及動力學的比較，希望以此新式樣的骨釘能成為將來皮質骨軌跡使用的骨釘首選。

In assessing the kinematics and dynamics of implants on the human body, methods often used include actual biomechanical experiments or finite-element method to obtain the effects of the implant; clinical experiments often accompanied by experimental design, funding, data recording and preservation, but for finite-element method, only need to construct geometric models and input various analysis parameters, you can get results close to the actual clinical experiment. Furthermore, digitized data can be recorded for multiple cases comparison or applying more investigation in detail, so finite-element method are often used in medical publications.
The common-used bone fusion surgery today has a Traditional Trajectory and a Cortical Bone Trajectory, and the performance or effect on the fixed section of the intervertebral disc and the operational adjacent section are most clinicians’ concern. However, few papers directly discuss (1) the differences between kinematics and dynamics, or (2) overestimate the diameter or length of surgical implants, and (3) even the model of finite-element method is too simple which leads to analysis bias. Therefore, this study used a complete five-segment lumbar vertebrae and sacral lumbar vertebrae model to analyze and compare the kinematics and dynamics differences between the Traditional Trajectory and the Cortical Bone Trajectory by parameterizing diameter, length and implantation trajectory of screws.
Currently, Cortical Bone Trajectory is a relatively new clinical minimally invasive surgery for the lumbar spine; therefore, many clinicians are using this surgical method gradually. However, the size of the bone screw is often limited by the size of the pedicle, so the screw with smaller diameters are used for surgical application to avoid penetrating the vertebral pedicles or vertebral body. However, most of researches indicate that bone screws with smaller diameters results in excessive stress and might break in actual use. Therefore, in this study, the pedicle screw of the cortical bone tracking will be improved, and a composite screw will be designed to achieve good performance during surgery, and it is not easy to break. Through finite-element method, we compared between the kinematics and kinetics of the pedicle screw before and after our improvement. We expect this latest style of screw can be the first choice in the future.

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