It does not happen often, but nearly 50 percent of spine surgeons perform surgery on the wrong level of the spine sometime during their career. This is not surprising: a variety of factors make it difficult to localize a precise operative site in the thoracic spine, such as obesity, osteoporosis, and anatomical variations in the number of rib-bearing vertebra or the distance between traditional spinal landmarks. To avoid surgery on the wrong vertebral level, a new successful technique is proposed in an article in the Journal of Neurosurgery: Spine, available online Nov. 4, 2011, at http://www.thejns.org.
In their article, "Avoidance of wrong-level thoracic spine surgery: intraoperative localization with preoperative percutaneous fiducial screw placement," Upadhyaya and colleagues describe a technique involving percutaneous placement of a fiducial screw in a specific thoracic vertebra to localize the appropriate operative site. Insertion of this minute screw is performed using computed tomography (CT) guidance and can be done preoperatively on an outpatient basis. On the day of the operation, radiographs or reconstructed CT scans can be referenced to confirm the operative level. The screw can be visualized intraoperatively using fluoroscopy. In this paper the authors assess the safety and efficacy of using a fiducial screw to guide appropriate-level surgery and compare its use with intraoperative fluoroscopy alone and a variety of other localization techniques discussed in the literature.
The authors performed a retrospective analysis of 26 patients who underwent percutaneous implantation of fiducial screws followed by minimally invasive or open thoracic spine surgery at the hand of the senior author, Dr. Praveen Mummaneni. Location of the screw was verified during surgery using fluoroscopy. The authors compared this patient group with a historical cohort of 26 patients (also treated by Dr. Mummaneni), in whom localization of specific vertebrae was made using fluoroscopy and a series of percutaneous needles to aid in counting vertebral levels. Wrong-level surgery did not occur in either group; however, the surgeon found that the fluoroscopic localization time is much shorter when one fiducial screw is used: 3 minutes rather than 15 minutes. Implantation of the fiducial screw requires CT, but the radiation exposure involved is less than that required for a spine radiograph and is offset by the reduced radiation exposure encountered during the shorter intraoperative fluoroscopy. The use of a fiducial screw is also cost neutral according to the authors: the added costs of the preoperative implantation procedure are offset by a shortened operative time.
The authors also discuss other techniques of localization, including use of radiographic skin markers, computer-assisted intraoperative navigation, injection of polymethylmethacrylate into the vertebral body, marking of the spinous process with methylene blue dye, and intraoperative transligamentous ultrasound localization. According to the authors' analysis, each one of these techniques fails in a comparison with percutaneous implantation of fiducial screws. Reasons for this include inaccuracy, unreliability, time wasted, and/or safety concerns.
The authors conclude, "The use of preoperative percutaneous fiducial screws for intraoperative localization of the target level in the thoracic spine is safe, efficient, and accurate for identifying the correct surgical level."
Looking back over the study, Drs. Wu and Mummaneni say, "Wrong-level surgery in the thoracic spine is especially problematic with minimally invasive approaches due to the limited field of view. The bony fiducial marker technique helps provide surgeons with a roadmap to the correct level of the spine. It removes the guesswork of counting spinal levels in patients with anatomical variations such as having an extra set of ribs."
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