Photogrammetric calibration of a C-arm X-ray system as a verification tool for orthopaedic navigation systems

For the total replacement of the knee joint, the precise reconstruction of the mechanical axis is significantly determined by the alignment of the cutting tool with respect to the rotation centre of the femur head. Operation techniques supported by navigation allow for the precise three-dimensional location of the hip centre by cinematic analysis. Recent results permit the reconstruction of the femur axis to be better than 0.7degrees. Therefore, conventional verification methods such as the post-operative recording of the complete leg are not suitable due to their limited system accuracy of about 2degrees. As the femur head cannot be accessed directly during the operation, an X-ray method has been used to verify alignment. The paper presents a method and the results achieved for the calibration of a C-arm system by introducing photogrammetric parameters. Since the method is used during operation, boundary conditions such as minimal invasive surgical intervention and sterility have been considered for practical applications of patients. (C) 2002 Elsevier Science B.V All rights reserved.