Embracing the future of spine navigation
Publish Date: 3/29/2012
Originally, spine surgery was performed with simple lateral and anterior/posterior x-rays but these cannot provide the all-important, axial view, which James T. Bennett, MD, from Tulane University, School of Medicine in his session “Navigation in Spine Surgery” says is the Holy Grail of spine navigation. The move to two-dimensional (2-D) navigational fluoroscopy was a giant leap in technology as well as the resultant quality of care, but it too does not provide an axial view. The 2-D method also does not use a preoperative computerized tomography (CT) scan.
Currently, techniques for image guidance surgical systems include preoperative CT and fluoroscopy-based image guidance (eg, three-dimensional (3-D) C-arm fluoroscopy, 3-D O-arm fluoroscopy). Preoperative CT-based systems have a digitizer, a digital localizer, and a computer workstation for image processing where images are reformatted. Three to five points are selected at each instrumental level for accuracy verification. However, trajectory errors are possible and a very small trajectory error can result in significant problems. The disadvantages to preoperative CT-based systems are that the preoperative study cannot account for changes in intersegmental relationships in positioning and this technique is not conducive to minimally invasive surgery.
Virtual fluoroscopy does not have surgeon-dependent registration and it limits occupational radiation exposure. Furthermore, images are acquired after surgical positioning, which avoids problems with intersegmental relationships in positioning. However, most systems do not offer the key axial view. Three-dimensional C-arm fluoroscopy
- obviates the need for obtaining a preoperative CT scan,
- allows the postoperative scan to be performed in the OR where implant placement can be assessed and revised immediately.
- decreases the incidence of malpositioned screws, and
- decreases surgeon radiation exposure.
Dr Bennett reminded attendees that one minute of fluoroscopy is equal to the radiation in 150 chest x-rays.
Spinal navigation and intraoperative imaging using an O-arm can be used in either the 2-D or 3-D mode. The 2-D mode memorized up to four positions. The 3-D mode can transfer images to the workstation in 13 seconds, provides automated registration, and has fast scan time (eg, 351 images over 360° in 13 seconds [standard definition] versus 750 images over 360° in 26 seconds [high definition]). The goals of 3-D O-arm spinal navigation is to
- improve the accuracy of spinal screw insertion;
- minimize or eliminate the need for fluoroscopy; and
- reduce surgical time, expense, and morbidity.
Image guidance navigation is an effective surgical technology, explained Dr Bennett, and there are a variety of applications for spinal deformity surgery. This technique allows for optimal preoperative planning and facilitates intraoperative orientation. However, image guidance navigation is not a substitute for knowing anatomy and using proper surgical technique. “You don’t know what you don’t know,” Dr Bennett said, so practitioners must learn fluoroscopic navigation first before using 3-D navigation.