document: State-of-the-art in orthopaedic surgical navigation with a focus on medical image modalities This paper presents a review of surgical navigation systems in orthopaedics and categorizes these systems according to the image modalities that are used for the visualization of surgical action . Medical images used to be an essential part of surgical education and documentation as well as diagnosis and operation planning over many years . With the recent introduction of navigation techniques in orthopaedic surgery , a new field of application has been opened . Today surgical navigation systems - also known as image-guided surgery systems - are available for various applications in orthopaedic surgery . They visualize the position and orientation of surgical instruments as graphical overlays onto a medical image of the operated anatomy on a computer monitor . Preoperative image data such as computed tomography scans or intra operatively generated images -LRB- for example , ultrasonic , endoscopic or fluoroscopic images -RRB- are suitable for this purpose . A new category of medical images termed ` surgeon-defined anatomy ' has been developed that exclusively relies upon the usage of navigation technology . Points on the anatomy are digitized interactively by the surgeon and are used to build up an abstract geometrical model of the bony structures to be operated on . This technique may be used when no other image data is available or appropriate for a given application
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