當脊椎滑脫或脊椎椎節不穩定時，常常需要使用椎弓根螺釘固定手術，但椎弓根螺釘固定手術是有一定困難度及危險性的，因為椎弓根是一個形狀不規則且內徑狹窄的通道，所以必須有一定的經驗及手術技巧，才能夠正確的植入螺釘，目前台灣臨床上還是以傳統的仰賴醫生經驗及手感的方式為主，然而鄰近椎弓根有主要的中樞神經及血管等，椎弓根螺釘如果植入位置或角度不妥，螺釘沒有在椎弓根內而是穿透皮質骨層外露，將有很大的可能性造成神經或血管損傷，此時應盡快進行二次手術做處理，以期能減輕因螺釘誤置所導致的後遺症，所以如何判斷椎弓根螺釘的植入情形是一個值得探討的議題。
本研究透過醫學影像的測量及利用椎體轉動角度(θ)公式與橫切面螺釘角度(TSA)公式，蒐集椎弓根及椎弓根螺釘的尺寸、角度及位置等資訊，蒐集完畢後則是將這些資訊匯入運算軟體MATLAB，椎弓根形狀類似橢圓柱體，所以用橢圓柱體簡化模擬椎弓根；而螺釘則是以圓柱模擬，再由測量得到的角度及位置等數據去擺放橢圓柱體及圓柱體，最後得到的結果即是椎弓根螺釘植入情況的模擬。
從實際案例的分析結果來看，θ公式的平均絕對誤差為2.1o；TSA公式的平均絕對誤差為3.5o，而模擬結果與實際影像情況的趨勢皆能吻合，故此方法用於術後的初步檢查是可行的。

Pedicle screw fixation is a difficult and dangerous surgery, because the pedicle is irregular in shape and narrow in its diameter. In order to insert the screw correctly, the doctor must be very experienced and skillful. At present, this surgery still be operated in traditional way in Taiwan, it means that the doctor insert the screw by their experience. There are central nervous system and vein close to the pedicle. Once pedicle screw is inserted inappropriate and penetrates the cortical bone, it may cause damage to the nerve or vein, and it should be treated as soon as possible to prevent the complication. Therefore, this is an important topic that how to judge the condition of pedicle screw insertion.
In this study, we collect the sizes, angles and locations of pedicle and pedicle screw by use of the measurement in medical images and two formulas which is used to obtain the rotation angle of vertebrae (θ) and transverse screw angle (TSA). After that, we simply simulate the pedicle by elliptic cylinder and screw by cylinder in MATLAB, and place these two objects based on the information we collected, then we will get the three dimensional simulate result of pedicle screw insertion.
The results from the analysis on real case show that mean absolute error of θ is 2.1 degrees and the mean absolute error of TSA is 3.5 degrees. And the trend of simulation is the same as real images. Therefore, we believe that it works for the postoperative inspection by this simulation method.

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