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Imaging and Navigation
Figure 1a: Result of Surface Matching of T5 During Navigated Figure 2: Positioning of Judet’s Screws in C2 with Computed
Dorsal Instrumentation of an Unstable T4 Fracture Tomography-based Navigation for Stabilisation of an Unstable
C1 Jefferson Fracture
Figure 1b: Result of Computed Tomography Fluoro Matching of
L2 During Navigated Anterior Corporectomy and Dorsal Wall
Resection After Dorsal Instrumentation of an Unstable L1
Fracture with Incomplete Paraplegia
Figure 3: Navigated Dorsal Wall Resection after Dorsal
Instrumentation of an Unstable L1 Fracture with Incomplete
Paraplegia (Patient from Figure 1b)
unstable fractures with neurological impairment, can also be performed automatically rotate around the patient while maintaining the pertinent
using image guidance (see Figure 3).
5
Despite the outstanding image quality spinal anatomy at its centre. Used in conjunction with specialised software,
of CT-based navigation, this technique has some distinct disadvantages. A the C-arm can function as a kind of CT scanner. It takes almost exactly one
pre-operative CT scan using a particular protocol is required, with associated minute for the automated image acquisition; these images are then
time costs. Sometimes a repeat scan is needed, especially when the patient reconstructed to provide axial, coronal and sagittal images of the spine.
was scanned for diagnostic reasons with a navigation-incompatible protocol During the scan, an apnoeic phase is required, otherwise the breathing
in another hospital. Time is also needed for pre-operative preparation of the motion causes a reduction of image quality. Loss of accuracy caused by
data sets. Furthermore, there is a learning curve for the procedure of respiration has been measured to be up to 1.3mm in the lumbar spine,
6
and
identification and registration of the anatomical landmarks. Complex even greater in the thoracic spine.
7
The C-arm is fitted with a calibration
anatomical structures or a lack of precise bone landmarks can lead to a target and the DRA is attached to the patient. The camera is then able to
prolongation of the registration progress and therefore of the operation track the position of the DRA in reference to the C-arm while the image
time. As the CT is taken prior to the operation, inter-segmental relationships acquisition is performed. Reconstructed images are transferred to the
are not presented and therefore changes between status at the time of the navigation system’s computer workstation and automatically uploaded into
scan and status at the time of the operation can be overlooked. the navigation software. An anatomical registration for the navigation is not
necessary. Nevertheless, verification of registration has to be performed in
Navigation with 3D C-arm Fluoroscopy the same way as in CT-based image guidance before the navigation can
3D fluoroscopy is a significant improvement in the rapidly developing sector start (see Figure 4). There are many advantages of this innovative technique,
of image guidance. In contrast to a standard fluoroscope, a C-arm is able to although image quality is still not as high as in conventional CT. Stöckle et
30 EUROPEAN MUSCULOSKELETAL REVIEW
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