手術後於臨床追蹤觀察發現，初期脊椎骨融合必須依靠內固定器作為穩定脊柱之功用，以促進骨融合速率。但人體會因自重負荷加上彎曲及扭轉之動作，使得脊椎內固定器螺絲與椎骨咬合界面會產生滑動現象，造成固定器之椎骨螺絲會有鬆脫、破壞與失去原有手術後之矯正度；為此如何提升固定器之椎骨螺絲的骨咬合強度，以提高脊柱之穩定度，成為脊椎內固定器設計的首要課題。
本研究目的即是評估椎骨螺絲傾角變化對此設計之前方板型固器於拉出強度的影響，因此建立三維前方板型固定器之拉出強度模型，並透過田口參數化方法來探討其參數的設計，經由資料解析，找出最佳設計之參數；最後將田口直交表設計之其中四組模型與最佳化模型進行生物力學拉出測試，並驗證數值分析與生物力學測試之相關性。
研究結果顯示，最佳設計為(A13A23A33A43D13D23D33)組合，其右側椎骨螺絲之橫切面傾角(A1)與左側椎骨螺絲之橫切面傾角(A3)為最重要設計因子，其次為右側椎骨螺絲之正前面傾角(A2)與左側椎骨螺絲之正前面傾角(A4)為次要設計因子；並於線性相關方法中發現，生物力學測試與有限元素模擬之相關係數為0.944，代表著有限元素模擬可以有效地預測生物力學測試。本研究之最佳螺絲植入傾角，有助於提高骨咬合強度，因此建議當前方板型固定器之椎骨螺絲植入椎骨時，考慮傾角鎖入，所形成之咬合三角面積，能有效抵抗椎骨螺絲產生的鬆脫現象，便能增進整體脊柱之穩定性。

Anterior vertebral plates (AVPs) can provide the initial stability in the fixation of spinal fractures or diseases. However, in clinical point of view the AVPs may fail after the surgical operation. One of failure modes for the AVPs is fixator loosening. This complication may cause loss of fracture fixation in the impairment of fracture healing and threaten the bone fusion rate. The purpose of this research was to evaluate the effects of the bone screw inclination angles on the designs of the AVPs regarding the pullout strength.
To investigate the pullout strength of the AVPs with different bone screw inclination angles, three-dimensional nonlinear finite element models were created and analyzed with use of ANSYS Workbench. Then, the parametric study was done by using Taguchi robust design methods. The optimum design and the significant factors for the AVPs were also obtained. Finally, the results of the finite element models would be validated by using the mechanical tests. The results showed that the transverse plane inclination angle in right side screw (30.7%) and the transverse plane inclination angle in left side screw (32.7 %) were important factors. The optimum combination of the AVPs was A13A23A33A43D13D23D33 (the transverse plane inclination angle in right side screw was 12°, the frontal plane inclination angle in right side screw was 5.5°, the transverse plane inclination angle in left side screw was 12°, the frontal plane inclination angle in left side screw was 5.5°, the distance between the right side screw and the middle of the AVP was 40 mm , the distance between the left side screw and the middle of the AVP was 40 mm , and the distance between the right side screw and left side screw was 16 mm). The reaction force obtained from the finite element analyses was closely related to the pullout strength obtained from the mechanical tests with a high correlation coefficient of 0.944.
In conclusion, the optimum AVPs can be acquired with use of Taguchi-based finite element methods. The validated finite element models can effectively predict the pullout strength of the AVPs. The result of this research can assist the engineers to design new AVPs and provide the biomechanical suggestions to orthopedic surgeons.

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