A novel radiographic technique to asses grafts in the female pelvis: a comparison of the Inside-Out and the Outside-In transobturator mid urethral sling positioning

The three-dimensional configuration of mid-urethral sling tapes is difficult to demonstrate in traditional anatomical dissections or imaging studies. The aim of this study was to test the utility of a novel technique using mesh tapes to assess spatial differences between the in-out and out-in transobturator mid-urethral slings. Two independent surgeons performed their usual transobturator mid-urethral sling placement on 10 fresh thawed cadavers, alternating sides in the consecutive cadavers. Tantalum wires threaded through the polypropylene-tapes rendered them radio-opaque. Following placement, CT scans were obtained to generate 3-D and MIPS images for analysis. Results showed that the mean angle formed by the in-out sling measured 122º (95%CI: 107º-136º); versus 144º (95%CI: 131º-151º) for the out-in sling (p = 0.02). The paired differences between the tapes’ inner angles were significantly different; with a mean difference of 20º (median 19.0º), (p = 0.008). There was no significant correlation between either approach and BMI or angle of the pubic arch. The images revealed that the tapes lie as a band posterior/dorsal to the urethra rather than inferior. In conclusion: marking mesh with Tantalum wire, in combination with 3-D and MIPS CT-scan reconstruction images, provided a unique method to visualize the entire sling trajectory. The clinical implications of the more horizontal positioning after the out-in approach remain to be determined.