The International Journal of Spine Surgery published an article examining intraoperative three-dimensional imaging for assessing pedicle screw position.
The study authors wanted to see whether the O-arm imaging prevented unacceptable screw placement. They examined 602 pedicle screws placed in 76 patients with intraoperative three-dimensional O-arm imaging.
If the screw had no breach, it was rated optimal; a 2mm breach or less was rated acceptable; a breach of more than 2mm was rated unacceptable. Here are five findings from the study:
1. There were 17 screws in 14 cases that were revised at the time of surgery on the basis of three-dimensional imaging. A previous study examining patients from 1966 to 2006 showed the average malposition rate for non-navigated screws was 9.7 percent, compared with 4.8 percent with navigated screws.
2. There were 37 cases using a two-dimensional fluoroscopy C-arm or O-arm; 23 cases using computer navigation O-arm image guidance; nine cases with anatomic landmarks; and 14 cases with previous screw tracks. On independent review of multiplanar images, the screws were rated:
• 1.8 percent were unacceptable
• 5.3 percent were acceptable
• 92.9 percent were optimal
All unacceptable screws were revised to an optimal or acceptable position and an additional six acceptable screws were revised to the optimal position.
3. The O-arm imaging prompted intraoperative repositioning in 2.8 percent of the pedicle screws. It identified the unacceptably placed screws so the surgeon could perform the revision without needing a reoperation.
A 2012 study examining 448 surgeries performed over five years compared cost and quality-adjusted life years of procedures that used isocentric O-arm fluoroscopy, neurophysiological monitoring and postoperative CT scanning after multilevel instrumented fusion for degenerative lumbar disease. The O-arm monitoring strategy was significantly less costly than the postoperative CT scanning following intraoperative uniplanar fluoroscopy, both of which were significantly less costly than neurophysiological monitoring.
At the same time, there were no difference in the clinical effectiveness of the three strategies, prompting the study authors to conclude O-arm was the most cost-effective strategy.
4. The CT has shown more accurate and reliable imaging method for evaluating screw position than plain radiography, according to the report, but isn't available in most operating rooms. The O-arm is a new generation intraoperative imaging system that can provide three-dimensional images.
"The results of this study indicate that the O-arm imaging system is useful in spine surgery, particularly in the setting of pedicle screw placement," concluded the study authors.
5. The O-arm has been used in conjunction with navigation or image guidance systems for pedicle screw placement, recently showing increased screw placement accuracy. A study using data from patients who underwent PLIF or TLIF with the O-arm or freehand shows a 94.1 percent accuracy in the freehand group and 99 percent accuracy in the O-arm group. The study authors estimated O-arm could reach 100 percent accuracy in the hands of an experienced surgeon.
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