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Imaging and Navigation
Intra-operative 3D Navigation and Imaging in Spine Surgery
a report by
Sebastian Katscher, Jan-Sven Jarvers and Christoph Josten
Department of Trauma and Reconstructive Surgery, Spine Centre, University of Leipzig
The field of spinal surgery has undergone tremendous evolution and rapid registration probe. This is supplemented by a process in which 12 random
technological advances in recent years. Before the appearance of image points are selected on the exposed surface of the vertebra. This provides the
guidance, surgeons relied on their knowledge of the anatomy of the spine navigation system with a contour map of the vertebra. The computer
complemented by images acquired pre-operatively and intra-operative workstation then quantifies the registration error as an index for the
fluoroscopic images. Plain radiography is commonly used to assist in accuracy of the matching procedure between the surgical anatomy and
localisation of the skin incision, identification of the proper anatomical level the computer display. The consensus in the literature is that registration
and confirmation of the correct positioning of spinal implants. However, errors <1.5mm can be accepted for most spinal procedures;
4
however, we
conventional methods such as these have several weak spots, even in the always aim for a registration error <1.0mm in the cervical region, as well as
hands of experienced surgeons: experimental and clinical studies
1–3
have in the upper and middle thoracic regions (see Figure 1a).
revealed pedicle screw misplacement rates of up to 20–30% using these
techniques. In contrast, image guidance provides 3D visualisation of the For CT fluoro matching, anterior–posterior and lateral fluoroscopic images
spine, which can be used for pre-operative planning and intra-operative are obtained using the C-arm. The C-arm is fitted with a calibration target
navigation, as well as for the confirmation of the accurate localisation of during the image acquisition. The computer workstation uses these images
concealed anatomical spinal structures that are cannot be directly visualised to obtain a congruent result with the pre-operative CT data (see Figure 1b).
during standard surgical exposures and fluoroscopy. This article provides a After both matching procedures, before any navigation is attempted
short review of the different types of intra-operative imaging, underlining anatomical verification of the registration accuracy must be performed. This
the general opinion of the current literature: that image guidance enables verification is achieved by touching the registration probe to several points
highly accurate intra-operative navigation with increased safety in complex on the selected vertebra and ensuring that the virtual probe is seen to be
spinal procedures. There are three commonly used methods of spinal touching the corresponding points on the multiplanar displayed CT images
image guidance: pre-operative computed tomography (CT)-based image on the monitor. The awls or other special tools can then be calibrated.
guidance, fluoroscopy-based image guidance and intra-operative 3D Navigated pedicle preparation is particularly useful in small pedicles, for
fluoroscopy. At our institution we use the CT-based and intra-operative example in the mid-thoracic spine and the cervical spine (see Figure 2).
3D methods; therefore, this article will focus on these two techniques. Anterior procedures, such as resection of posterior wall fragments in
Computed Tomography-based Image Guidance
Prior to surgery, a CT scan is taken of the relevant region of the spine, using
Sebastian Katscher is a Consultant in the Department of
Traumatology and Reconstructive Surgery at the University
thin axial slices (1–2mm). The data from this scan are transferred to the of Leipzig. He specialises in spine surgery, with a focus on
computer workstation through a local network connection. The data are
less invasive endoscopic-assisted and navigated procedures.
He is a member of AO Spine and the German Society of
then prepared for use in the navigation system in the operating room (OR)
Spine Surgery.
and transferred to the OR system using a hardware carrier. The OR system
E:
sebastian.katscher@medizin.uni-leipzig.de
consists of several components, including an electro-optical camera array, a
surgical reference system (dynamic reference array, DRA) and various
customised spinal instruments, for example awls. The optical tools are
Jan-Sven Jarvers is an Assistant Doctor in the Department of
Traumatology and Reconstructive Surgery at the University of
connected to the instruments and the DRA and are tracked by the camera
Leipzig. He graduated in human medicine in 2007 from the
array in order to calculate their position in 3D. In addition, there is a
University of Leipzig and the University of Parma, with a
doctorate on ‘The navigated isolated ventral monosegmental
computer workstation that runs the system software and functions as the
stabilisation of thoracolumbar A1.2 and A 3.1 fractures’.
primary system interface. The system software consists of programs able to
transfer CT data to the workstation, as well as registration and surgical
planning options. The next step is patient registration, which provides a
correlation between the operative anatomy and the pre-operative CT
Christoph Josten is Director of Trauma and Reconstructive
Surgery at the University of Leipzig. Prior to this he was a
anatomy as shown on the monitor. In order to perform the registration, a Consultant at Ruhr-University Trauma Hospital, specialising
navigation clamp (DRA) is fixed on the spinous process of a vertebra. Two
in orthopaedic trauma, intensive care medicine and hand
surgery. Professor Josten is co-editor of and a reviewer for
different methods of registration are possible: surface matching or CT fluoro
several journals, as well as serving on the Executive Board
matching. For surface matching, the registration begins by determining a of the German Society of Trauma Injury and the Indo-
start point on the spinous process and choosing eight specially prescribed
German Orthopaedic Association. He completed his medical
studies at Saarland University in 1979.
anatomical points (the superior facet, the inferior facet and the base and tip
of the spinous process on both sides) of the selected vertebra with a
© TOUCH BRIEFINGS 2008 29
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