What do you demand of pre- and intraoperative imaging in spinal surgery?
RUDOLF BEISSE: We need a high-contrast, high-resolution image of anatomical structures, including those in critical transitional zones, that is accurate down to the smallest detail. In conventional X-ray examinations in two planes, the three-dimensional topographic anatomy of the bones and soft tissue can only be assessed to a limited extent. A three-dimensional view is also helpful in the case of post-traumatic and other deformities of the spine. Here, decisions can be made in advance as to the best surgical approach to correct the deformity.
Which option do you prefer for 3D imaging?
When planning a very complex corrective procedure to the spine, we still prefer pre-operative computed tomography (CT) with 3D reconstruction. Alternatively, I take an X-ray myself directly in the operating theater. This removes one step in the pre-operative process, reduces radiation exposure and has the advantage that the imaging data reflect the exact position of the patient during the operation. This data can also be used directly for navigation.
When do you think 3D imaging is necessary in the operating theater?
I think 3D imaging is needed in an operating theater, for example, during reconstructive surgery to the tibial head, the upper and lower ankle joints and to the spine during operations on the critical areas of the upper cervical vertebrae, the thoracic spine, and the lumbosacral transitional zone. The imaging gives me information as to whether the repositioning or reconstruction was successful during the operation itself and so I can make immediate corrections if required. We also need the option of recording a 3D dataset for navigation
What advantages does 3D imaging offer compared with 2D display in terms of the quality of outcomes and the safety of procedures?
If you think of how many structures are projected onto one layer in a 2D image, it is clear that it will never be possible in this way to determine the layer at which a displacement in the joint, for example, has actually occurred. Another problem is the misplacement of pedicle screws: If the tip of the screw in the anterior posterior view is behind the midpoint of the vertebral body, it is most probably malpositioned. With the 3D image, however, you can establish the exact position of the screw tip and whether it is touching the vertebral canal. The misplacement rate for pedicle screws when using 2D imaging is given as four to 40 percent. This does not always necessarily lead to neurological problems, but certainly has consequences for biomechanical anchoring strength and, therefore, for potential complications. Thanks to 3D technology, operations have become safer.
In practice, how do you deal with the permanent conflict between obtaining the highest possible quality in images while achieving a low radiation dose?
The increased radiation exposure limits the possibilities for repeated 3D imaging when using computed tomography. In 3D imaging with navigation, the Siemens ARCADIS® Orbic 3D allows us to work in low- or high-resolution mode. To confirm satisfactory repositioning, it is sufficient to use half the radiation dose to produce a comparatively low-resolution control image. In high-risk surgical procedures, the significance of radiation exposure tends to be outweighed by practical considerations.
How do you rate the overall radiation exposure in 3D imaging compared with working with 2D C-arms?
I think that the overall radiation dose applied to patients has remained about the same, and if anything has tended to decrease. Keeping the surgeon – who spends most of their working life in the operating theater at the X-ray machine – outside of the radiation field when collecting the data is a major step forward.
What were the key reasons for choosing the C-arm?1
My reasons for using the Siemens technology for intraoperative 3D imaging relate particularly to the potential for combining 3D imaging with navigation, which has worked smoothly for many years and uses a lower radiation dose compared with competitor products. For someone like me, who worked with the first-generation Iso-C-3D image converter, the components are simple to operate. They are based on a logic that remains comprehensible even when new products are introduced. The operating surgeon can trust that newly acquired devices can be integrated into the existing infrastructure. During the operation, the isocentric C-arm can be used with 190 degrees orbital rotation to make visible a volume of approximately 12 x 12 x 12 centimeters (4.7 inches). For the spine, this enables two to three vertebrae and the surrounding soft tissue to be captured in a good quality image. This is usually sufficient for trauma surgery and for navigation in this area. We must also consider that our patients are becoming ever older. The bone structures of those undergoing surgery are worsening. Unfortunately, we are also seeing increasing numbers of overweight patients, which has a negative effect on the contrast between soft tissue and bone and also makes it difficult for us to identify areas on the X-ray image. Modern devices make this possible. Operability has improved, which ultimately makes communication in the operating theater easier and speeds up processes during the surgery.
Surgical procedures are tending to be less and less invasive. How far do you believe this trend can continue and to what extent is imaging significant in this?
The use of so-called minimally invasive procedures is often cited as a popular criterion, as though automatically guaranteeing quality of care. It is correct that access trauma or soft tissue trauma should be minimized as far as possible. Nevertheless, steps must be taken to ensure that the quality of the results remains the same as in open surgery. The moment that compromises are made here in favor of a smaller incision is the moment that a line is drawn or may already have been crossed.
3D imaging combined with navigation has made it possible for spinal accesses to be exactly the same size and in precisely the same place where we would ideally drill or insert screws into the bones. In contrast to preoperative CT-based navigation, we can begin the navigated procedure without further referencing. Prolonged exposure of the site of the operation for surface referencing is not necessary, saving time and reducing radiation exposure.
What might the operating theater of the future look like?
In my view, a realistic scenario – and indeed one in which some aspects have already been realized – is that sources of information about a patient and the technical aids in the operating theater will in future be combined and visually presented. For endoscopic surgery on the spine, it would be desirable for the endoscopic image to be overlaid with the bone structure, be it from the CT or MRI data record. The ARCADIS Orbic 3D system already has the appropriate software. Large centers will still have CT and MRI machines directly in their operating theaters. Customary care facilities require endoscopy, navigation, and 3D imaging to provide the quality that today’s patients have the right to expect.