3D IMAGING Dr. Gary uses a 3D C-arm to intraoperatively evaluate the reduction of the fracture and the screw placement.

Are the pedicle screws precisely inserted? Is the ankle fracture perfectly aligned? Before the arrival of 3D C-arms, surgeons couldn't verify that the implant was sitting in the anatomically correct position or validate that the fracture was optimally reduced without using a separate O-arm or waking the patient and wheeling him to the radiology lab for a scan. But thanks to intraoperative 3D imaging provided by a standard C-arm, I can be certain that the screws and the bones are positioned exactly as they should be — while the patient is still in the room. In 2 minutes, our fluoroscopy tech rotates the C-arm around the patient, capturing CT-like images of our handiwork that spin in 3 planes — axial, sagittal and coronal — on the flat-screen monitor.

This is a tremendous leap forward in surgical imaging. Because I don't have to wait for the results of a post-operative CT scan, I can make a correction, if necessary, intraoperatively instead of scheduling a revision surgery or accepting a suboptimal reduction to avoid a second anesthesia. Nothing lets surgeons control the radiographic outcome of their intervention and check the results of their surgical technique like an intraoperative 3D scan.

As an orthopedic trauma surgeon at the University of Texas Health Science Center at Houston, I've been using a 3D C-arm for a little more than a year. A 3-dimensional device is best suited for intraoperative use in orthopedic and spine surgery, as well as trauma cases, when precise imaging and perfect visualization matter most.

Clinical utility
In trauma and orthopedic surgery, the precise identification and reduction of fractures and the accurate placement of implants is often critical to clinical outcomes. Several studies have demonstrated that CT scans are superior to 2D imaging for detection of malreduction and malposition of implants. Malpositioning of spinal implants can have devastating consequences, including paralysis or damage to great vessels, including the aorta.

EXACT ANATOMY IMAGING
Understanding the Principle of Isocentricity

CIRCULAR ARC Isocentric C-arms move in a perfect circle around the subject while other models rotate in an egg shape, says Block Imaging's Chris Sharrock.

For a C-arm to be considered "isocentric," the central X-ray beam must remain in the isocenter of the subject regardless of the position of the C-arm. The distance of the X-ray tube and the image intensifier from the subject does not change, allowing consistent image size throughout a scan.

An orbital rotation far beyond that of a standard C-arm is required to maintain isocentricity and perform 3D imaging with orbital movement. This eliminates patient repositioning during procedures which, in turn, reduces radiation dose and saves time.

Among the current 3D C-arm models on the market, the Siemens Arcadis Orbic 3D, featuring 190 ? orbital rotation, is the only system that is truly isocentric. The Philips BV Pulsera 3D and Ziehm Vision Vario 3D compensate for this with software applications, but their 3D modeling is based on formulas as opposed to actual anatomical images.

— Chris Sharrock

Mr. Sharrock ([email protected]) sometimes referred to as the "The C-arm Guy," is the fluoroscopy product manager at Block Imaging, a C-arm refurbisher in Holt, Mich.

Take an ankle fracture with an associated syndesmotic injury, for example. On a 2D image, it's difficult to see that you've get the bones lined up right. A malreduced syndesmosis results in worse long-term functional outcomes and traditionally has been best assessed with a post-operative CT scan. Revision of the reduction would require a second anesthesia and surgery. Having CT-like technology in the OR is the best way to assess the reduction and make an adjustment. Similarly, my spine surgeon colleagues have shared with me that they can detect and correct pedicle screw misplacements intraoperatively with 3D C-arm imaging.

In addition to eliminating post-op scans, 3D C-arms can also create efficiencies in the emergency room. Instead of forcing fracture patients, for example, to wait for an X-ray in radiology and then sit around for test results, we can bring them right to the OR and scan them there.

You can easily position the C-arm during all kinds of procedures and effortlessly roll it from one room to another (I would use the 3D C-arm in every cases if I could, but that'd be overkill). 3D C-arms might also let you shrink your surgical footprint, letting you make reductions with smaller incisions or even doing so percutaneously. For example, imagine being able to assess a fracture within the joint cartilage without direct visualization. This added functionality is why there is great potential for 3D C-arms to be a disruptive technology.

CONFIRMATION The 3D image shows fixation of an acetabular fracture with columnar screws. The image demonstrates acceptable reduction and that the implants are extra-articular and correctly positioned within the bone.

Buying tips
For the 3D capability, expect to pay $75,000 to $100,000 more than your standard C-arm. Today's standard C-arms cost $100,000 to $150,000. A 3D C-arm runs between $200,000 and $250,000.

A few purchasing considerations:

• 2D and 3D in one? The 2 mobile 3D C-arms my hospital purchased combine 2D and 3D functionality in one device. That's right: The same machine that takes our standard fluoroscopic pictures also brings CT-like images to the OR. Note that not all 3D C-arms can be used as a regular C-arm, as ours can.
• Surgical navigation. If your facility uses surgical navigation, be sure that the 3D C-arm you choose can integrate with the current system. You need to be able to send fluoroscopic images over to your navigation system so you can use the navigation device during surgery.
• Isocentricity. You also want to make sure that the central beam always remains in the isocenter, which eliminates the need for repositioning and enables both time and dose savings (see "Understanding the Principle of Isocentricity"). Rather than moving the C-arm up and down and side to side when you rotate the C-arm, the C-arm will fixate on the anatomy you're imaging, automatically putting it in the center of the field.

Like any new technology, 3D C-arms are far from perfect. The intraoperative image quality is clearly not of the quality you'd get from a post-op CT scan. But 20 years ago, CT scans weren't what they are today. Things don't happen overnight. OSM