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Imaging and Navigation
Figure 4: Navigated Screw Placement in T4 and Post-operative
time costs; this is also true of the time-consuming pre-operative work on
Computed Tomography Control in a Patient with Osteolytic T5
data sets. Furthermore, the need for anatomical registration is completely
Metastasis and Spinal Canal Compromise
abolished, as navigation can start immediately after the images have been
transferred to the workstation. Finally, a post-operative control scan can be
taken in the OR to ensure the accuracy of implant placement (see Figure 5).
Incorrect screw placements can thus be corrected immediately, saving time
and avoiding expensive revisions.
9
The main disadvantage is the high cost of
the system; it may also be necessary to make other purchases, for example
a carbon operation table as metal artefacts affect image quality.
Comparison of Image-guidance Techniques and
Non-navigation Screw Placement
There are many investigations – both clinical and in laboratories – that
have analysed the accuracy of commonly used navigation techniques.
Kosmopoulos et al. drew up a meta-analysis of the current literature and
found that navigation provided higher accuracy in the placement of
pedicle screws for the sub-groups presented. Overall, the median
placement accuracy in the in vivo navigation-assisted sub-group (95.2%)
was higher than that in the unnavigated subgroup (90.3%). The report
included 130 studies with a total of 37,337 implanted pedicle screws.
10
Amniot et al.
11
compared 100 patients who underwent placement of
pedicle screws (T5–S1) using conventional fluoroscopy with 50 patients
who were operated on using pedicle screw placement (T2–S1) using
computer-assisted image guidance. In the conventional fluoroscopy
group, 461 of 544 screws (85%) were found to be accurately placed
compared with 278 of 294 screws (95%) in the computer-assisted
image-guided group. The issue of the radiation dose for both the patient
and the surgeon is still the topic of many investigations. In a comparison
between navigation with 3D rotational radiographic data and
fluoroscopic guidance, Von Walsum and his workgroup
12
analysed
Figure 5: Intra-operative Control with 3D Fluoroscope radiation exposure at the surgeons’ hands and measured lower values for
After Screw Fixation of an Unstable Odontoid Fracture
3D rotational radiography. Although the vast majority of the literature
(Anderson/D’Alonzo II)
emphasises the increased safety and accuracy of image-guided spinal
surgery, it is important to be aware of potential problems with each of
the modalities. These concern data acquisition through to data transfer
and data set preparation and, in particular, the intra-operative use of
computer navigation. In addition, software and hardware problems can
slow down the workflow. Those who are beginning to use such systems
should undergo a specialised introductory training course, ideally
followed by supervised training from surgeons who are sufficiently
experienced and well-informed about the possible sources of error. Only
then will the identification and subsequent avoidance of complications in
image-guided navigation be possible.
13
al. stated that their experiences were very positive, and the system was Conclusions
extremely reliable and precise in their experimental and clinical trials. Over Intra-operative spinal image guidance has evolved rapidly in the last few
the course of 160 drilling procedures, they reported a failure rate of only years. Through the technical improvement of navigation systems, the
4.2%.
8
The problem of navigation inaccuracy due to inter-vertebral safety of spinal procedures – especially in critical regions with small
alignment differences between the pre-operative CT data set and the intra- pedicles, such as the cervical spine and the upper and middle thoracic
operative image presentation is eliminated. Since the system can display up spine – could be increased. The new development of intra-operative 3D
to three adjoining vertebrae at once, separate registration solutions appear image guidance can be seen as a potentially important tool in spinal
not to be necessary. The need for a pre-operative CT scan with a specific surgery. As with all novel technologies there is a learning curve, which
image-guided protocol is eliminated, along with its associated financial and can be overcome with training and experience. ■
1. Castro WH, et al., Spine, 1996;21:1320–24. 149–56. 10. Kosmopoulos V, Schizas C, Spine, 2007;32:111–20.
2. Laine T, et al., Eur Spine J, 2000;9:235–40. 6. Glossop N, Hu R, Spine, 1997;22:903–9. 11. Amiot LP, et al., Spine, 2000;25:606–14.
3. Schulze CJ, et al., Spine, 1998;23:2215–20. 7. Grützner PA, et al., Chirurg, 2004;75:967–75. 12. Van Walsum T, et al., J Vasc Interv Radiol, 2006;17:
4. Rampersaud YR, et al., Spine, 2000;25:2637–45. 8. Stöckle U, et al., Unfallchirurg, 2006;109:925–31. 1511–18.
5. Katscher S, Josten C, Trauma Berufskrankheit, 2007;9: 9. Hüfner T, et al., Unfallchirurg, 2007;110:14–21. 13. Arand M, et al., Trauma Berufskrankheit, 2005;7:311–16.
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