Spinal instrumentation has become an integral part of modern spinal surgery as it allows us to achieve the goals of spinal decompression, stabilization in the presence of instability, correction of deformities, or excision of tumors very successfully. However, spinal instrumentation is not without risk, and ample evidence indicates that it has a high potential for dangerous complications (1,2,3,4). Pedicle screw fixation, with its numerous advantages over other methods of fixation, has become the most commonly used form of spinal fixation, but it requires a significant learning curve and has the potential for neural and vascular complications, especially in the thoracic (1,2,5) and cervical spine (3,4).The pedicles of the thoracic spine are smaller, and more chance of neural damage exists because of a decreased canal-to-cord ratio in this region (1,2). Intracanal placements of the screws are more dangerous in the thoracic region because of cord injury than in the lumbar region, where only nerve roots are found. Similarly, the peculiar anatomy of the pedicles in the cervical spine, its wide anatomic variation within the population, and its proximity to both the vertebral artery and the cervical cord are serious deterrents for the spinal surgeon to use this method of fixation in this region (3)

The technique of pedicle screw insertion is usually “blind,” because the pedicles are not visible directly, and the success of the procedure depends to a large extent on the anatomic landmarks and the experience of the surgeon. As a result, misplacement of the screws has been reported in 10% to 40%, especially when computed tomography (CT) scans are used to assess the postoperative position of the screws (6). The procedure becomes additionally challenging when the anatomy of the spine is altered, as in the presence of deformity such as scoliosis and kyphosis, or if an instability with altered intervertebral segmental displacement exists, such as seen in severe spondylolisthesis, posttraumatic displacements, or inflammatory disorders of the cervical spine (3,5,7,8).

Although freehand technique is commonly used, most surgeons opt for intraoperative fluoroscopic guidance in the presence of altered anatomy. These require the aid of an expert radiographer, as the fluoroscope tube must be tilted and rotated frequently to identify the end-on view of the respective pedicles. In the presence of severe deformities, exact identification of the pedicles is sometimes impossible. Multiple fluoroscopic exposures may be required, and the surgeon who is in the operating field has the risk of increased radiation exposure (9,10).

The need for improved accuracy and consistency in the placement of pedicle screws has led surgeons to probe into the application of computer-navigated spine surgery (11). Numerous reports prove the superiority and usefulness of navigation procedures in
achieving a higher rate of accuracy in spinal instrumentation (8,11,12,13,14). The initial software for the navigation was CT-based; the data acquisition was secured by preoperative CT scans. The increased setup and surgical time due to the need for intraoperative registration at every single level and registration-related errors were a major drawback to the CT-based navigation systems, which rely on acquired data before surgery. The change in the intersegmental vertebral anatomic relations in unstable situations also has been reported with navigation systems using preoperative CT scans. It would be ideal to have intraoperative data acquisition, in which these disadvantages would be overcome. Intraoperative CT/magnetic resonance imaging (MRI)-based navigation systems are now more accurate but not widely applicable because of the unacceptably high cost (9,10). They also occupy much space in the operating theater and the specific compatible operating tables, anesthetic apparatus, and instruments increase the cost. The radiation exposure to the operating surgeon and the increased chances of infection are other added disadvantages.

Iso-C 3D navigation, which helps to acquire the data intraoperatively after the patient is positioned and surgical exposure is completed, overcomes these discussed disadvantages (9,12). The acquired data from the Iso-C 3D is directly transferred to the navigation machine by an interface, and this helps to obtain accurate real-time images, avoiding registration-related errors. Many reports detail the use and accuracy of Iso-C-based navigation in the spine literature (7,12,13,14

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