本研究目的在發展人工膝關節術後之定位技術，使用兩張醫用數位影像判讀股骨元件與脛骨元件之三維CAD模型於空間上之實際位置關係，以便進一步研判人工膝關節裝配位置的準確性。而本研究主要是由二維數位X光影像取得人工膝關節置換物之影像資料，且依據影像處理後之相關資訊計算置換物之幾何關係與影像邊界輪廓搜尋，並進行定位點與定位軸辨識，再建立置換物元件於前視圖與側視圖影像之二維座標系統。另外，使用逆向工程掃描技術，建立人工膝關節的三維CAD模型，並計算二維影像與CAD模型之座標轉換關係。依據CAD模型與影像資料於兩視角影像之輪廓誤差，進行誤差迭代以修正旋轉角度，使其正確地達到三維CAD模型與數位X光影像資料的定位。並以電腦模擬結果顯示此一術後定位演算法已達到合理的定位結果，且其均方根誤差接近於影像的解析度，以證明所發展之術後定位演算法確實可行。 The objective of this research is to develop a registration algorithm for the X-ray images in total knee arthroplasty(TKA). Two views of the X-ray images for the TKA implant are employed to determine the pose of the three-dimensional CAD model between the femur and tibia components. So as to access the accuracy of the assembly. This research emphasizes the acquisition of the image data of implants from 2D X-ray images. The geometric characteristics of the implant images are analyzed and their boundary profiles are recognized. A positioning point and a positioning axle are obtained from the above analysis. A 2D coordinate system is built on each component of each view. A 3D CAD model acquired by reverse engineering is employed. An optimization algorithm is developed to optimize the contour error between the two-dimensional projection of the 3D CAD model and 2D X-ray images, where an unknown rotational axis is determined. After the optimization, the root-mean-square error between both profiles of the 3D CAD model and X-ray images is minimzed. An extensive study of the computer simulation has been presented to demonstrate the feasibility of the proposed method.