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Chair for Computer Aided Medical Procedures & Augmented Reality
Lehrstuhl für Informatikanwendungen in der Medizin & Augmented Reality

S. Weidert, L. Wang, P. Thaller, J. Landes, A. Brand, N. Navab, E. Euler
X-ray Stitching for Intra-operative Mechanical Axis Determination of the Lower Extremity
the 11th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery, London, UK, June 15-19 2011 (bib)

The correct mechanical alignment of the lower extremity plays an important role in preventing osteoarthritis, especially of the knee. For this reason, the verification of this axis is critical for reconstructive surgery as well as trauma surgery of long bones of the lower limb. The mechanical axis of the lower limb is a straight line defined by the center of the femoral head and the center of the ankle joint, ideally passing the knee joint in its center. Deviations from the standard range of the alignment can cause higher risk of knee disorders. Whereas the usual preoperative method to determine the mechanical axis of the lower limbs is still the long standing radiograph, common intra-operative methods are the use of an electrocautery cord or an X-ray grid consisting of lines underneath the patient. Both methods require the surgeon to bring the femoral head and the ankle joint exactly to overlay with an x-ray visible line that passes through both points. The distance of the knee center from this line is seen as the mechanical axis deviation (MAD). In order to reduce the errors introduced by perspective projection effects, the joint centers must be placed in the center of the images, often resulting in multiple X-rays. For this reason, those methods definitely require time, experience and many X-ray images. In order to enhance that procedure, we propose a computer aided X-ray stitching method that puts individual X-ray images into a panoramic image frame using the Camera Augmented Mobile C-arm (CamC) system with an optical marker pattern underneath the operating table.
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